Title of Invention	"SEMICONDUCTOR CERAMIC COMPOSITION AND PROCESS FOR PRODUCING THE SAME"
Abstract	This invention provides a semiconductor ceramic composition comprising BaTiO<sb>3</sb>, in which a part of Ba has been replaced with Bi-Na, which semiconductor ceramic composition can suppress the vaporization of Bi in a calcination process, can prevent a deviation of composition of Bi-Na to suppress the formation of a dissimilar phase, can realize a further reduction in electrical resistivity at room temperature, and can suppress a variation in Curie temperature, and a process for producing the same. Calcined powder of Ba(TiM)O<sb>3</sb>, wherein M represents an element which has been converted to a semiconductor, and calcined powder of (BiNa)TiO<sb>3</sb> are provided separately ...

Title of Invention

"SEMICONDUCTOR CERAMIC COMPOSITION AND PROCESS FOR PRODUCING THE SAME"

Abstract

This invention provides a semiconductor ceramic composition comprising BaTiO<sb>3</sb>, in which a part of Ba has been replaced with Bi-Na, which semiconductor ceramic composition can suppress the vaporization of Bi in a calcination process, can prevent a deviation of composition of Bi-Na to suppress the formation of a dissimilar phase, can realize a further reduction in electrical resistivity at room temperature, and can suppress a variation in Curie temperature, and a process for producing the same. Calcined powder of Ba(TiM)O<sb>3</sb>, wherein M represents an element which has been converted to a semiconductor, and calcined powder of (BiNa)TiO<sb>3</sb> are provided separately ...

Full Text	DESCRIPTION TECHNICAL FIELD The present invention relates to a semiconductor ceramic composition having a positive resistive temperature, which is used for a PTC thermistor, a PTC heater, a PTC switch, a temperature detector and the like, and a process for producing the same. BACKGROUND ART As materials showing a PTCR characteristic (Positive Temperature Coefficient of Resistivity), compositions in which various semiconductor dopants are added to BaTiO3 have been conventionally proposed. These compositions have a Curie temperature around 120°C. Depending upon the use, it becomes necessary for these compositions to shift the Curie temperature thereof. It has been proposed to shift the Curie temperature by adding, for example, SrTiCh to BaTiO3. However, the Curie temperature shifts only to a negative direction and does not shift to a positive direction in this case. Currently, only PbTiOa is known as an additive material for shifting the Curie temperature to a positive direction. However, since PbTiOs contains an element that causes environmental pollution, a material using no PbTiO3 has been demanded in recent years. Regarding BaTiO3 semiconductor ceramics, there is proposed a process for producing a BaTiO3 semiconductor ceramic by adding one or more of Nb, Ta and rare earth elements to a composition having a structure of Baj.(BiNa)TiOa, wherein a part of Ba m BaTiO3 m which no PbTiO3 is used is substituted with Bi-Na and x is controlled to be in a range of 0 Patent Document 1 JP-A-56-169301 DISCLOSURE OF THE INVENTION PROBLEMS THAT THE INVENTION IS TO SOLVE Patent Document 1 discloses m Examples, mixing, before calcination thereof, all the constituents such as the starting matenals including BaCO3, T1O2, B12O3, Na203 and PbO, followed by calcining, forming, sintering and heat-treating However, m the composition where a part of Ba of BaTiO3 is substituted with Bi-Na, when all the constituents are mixed before calcination thereof as in Patent Document 1, men Bi may evaporate during the calcination step to cause compositional deviation m Bi-Na, whereby the formation of different phases is accelerated, and increase in the resistivity at room temperature and fluctuation of the Curie temperature may be caused It may be considered to perform calcination at a low temperature for restraining the evaporation of Bi However, although the evaporation of Bi is certainly restrained by this method, a complete solid solution cannot be formed and the desired characteristics cannot be obtained An object of the invention is to provide a semiconductor ceramic composition containing no Pb, which is capable of shifting the Cune temperate to a positive direction and of widely reducing the resistivity at room temperature, and to provide a production process of the same Further, it is another object of the invention to provide a semiconductor ceramic composition m which a part of Ba m BaTiCh is substituted with Bi-Na, which is capable of restraining the evaporation of Bi in the calcination step, is capable of restraining the compositional deviation of Bi-Na thereby suppressing the formation of different phases, is capable of further reducing the resistivity at room temperature, and is capable of restraining the fluctuation of the Cune temperature, and to provide a production process of the same MEANS FOR SOLVING THE PROBLEMS As a result of intensive studies for attaining the above objects, the inventors have found that, in producing a semiconductor ceramic composition m which a part of Ba m BaTi03 is substituted with Bi-Na, when a calcined Ba(TiM)03 powder (M is a semiconductor dopant) and a calcined (BaNa)Ti03 powder are separately prepared and the Ba(TiM)03 powder is calcmed at a relatively high temperature while the (BaNa)Ti03 powder is calcmed at a relatively low temperature, both at the most suitable temperatures for them, then the evaporation of Bi from the calcmed Ba(TiM)03 powder may be retarded and the compositional deviation of Bi-Na may be thereby suppressed to inhibit the formation of different phases, and when these calcmed powders are mixed, formed and sintered, then a semiconductor ceramic composition which has a low resistivity at room temperature and is capable of restraining the fluctuation of the Cune temperature can be obtained The invention provides a process for producing a semiconductor ceramic composition m which a part of Ba of BaTiO3 is substituted with Bi-Na, the process comprising a step of prepanng a calcined powder of Ba(TiM)03 (wherein M is a semiconductor dopant), a step of prepanng a calcined powder of (BiNa)Ti03, a step of mixing the calcined powder of Ba(TiM)03 and the calcined powder of (BiNa)Ti03, and a step of forming and sintering the mixed calcined powder The invention further proposes, in the production process of the above-mentioned constitution a constitution in which a calcination temperature in the step of prepanng the calcined powder of Ba(TiM)03 is from 900 to 1300°C, a constitution m which a calcination temperature in the step of prepanng the calcined powder of (B£Na)Ti03 is from 700 to 950°C, a constitution in which a dry mixing is conducted m the step of mixing the calcined powder of Ba(TiM)03 and the calcined powder of (BiNa)Ti03, a constitution in which 3 0 mol% or less of Si oxide and 4 0 mol% or less of Ca carbonate or Ca oxide are added before the calcination in the step of prepanng the calcined powder of Ba(TiM)03 or the step of prepanng the calcined powder of (BiNa)Ti03 or in both the two steps, a constitution in which 3 0 mol% or less of Si oxide and 4 0 mol% or less of Ca carbonate or Ca oxide are added in the step of mixing the calcined powder of Ba(TiM)03 and the calcined powder of (BiNa)Ti03, a constitution m which the semiconductor dopant M is at least one of Nb and Sb, and the semiconductor ceramic composition is represented by a composition formula [(BiNa)Bai-]fTii-yMy]O3 in which x and y each satisfy 0 a constitution m which the ratio of Bi to Na satisfies a relationship that Bi/Na is 0 78 to 1 The invention also provides a semiconductor ceramic composition obtained by forming and sintering a mixed calcined powder containing a calcined powder of Ba(TiM)03 (wherein M is a semiconductor dopant and is at least one of Nb and Sb) and a calcined powder of (BiNa)Ti03, wherein the composition is represented by a composition formula [(BiNa)xBai-x][Tii-yMy]O3 m which x and y each satisfy 0 ADVANTAGE OF THE INVENTION According to the invention, there can be provided a semiconductor ceramic composition capable of rising the Cune temperature and capable of greatly reducing the resistivity at room temperature without using Pb that causes environmental pollution According to the invention, there can be provided a semiconductor ceramic composition capable of restraining the evaporation of Bi in the calcination step, capable of restraining the compositional deviation in Bi-Na to thereby inhibit the formation of different phases, capable of further reducing the resistivity at room temperature, and capable of restraining the fluctuation of the Cune temperature BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 is a graph showing the X-ray diffraction patterns of a semiconductor ceramic composition of the invention at different calcination temperatures Fig 2 is a graph showing the X-ray diffraction patterns of a semiconductor ceramic composition of Comparative Example at different calcination temperatures BEST MODE FOR CARRYING OUT THE INVENTION In the step of preparing a calcined powder of Ba(TiM)O3 (M is a semiconductor dopant) in the invention, first, BaCO3 and T1O2 as mam starting materials and ND2O5 or SO2O3 as a semiconductor ingredient are mixed to prepare a mixed starting powder, and then the powder is calcined The calcination temperature is preferably m the range of from 900 to 1300°C, and the calcination time is preferably 0 5 hours or more When the calcination temperature is lower than 900°C or the calculation time is shorter than 0 5 hours, Ba(TiM)03 is not completely formed, and the unreacted BaO may react with water in the atmosphere or in the mixed medium to unfavorably cause compositional deviation On the other hand, when the calcination temperature exceeds 1300°C, then a sintered body is generated in the calcined powder, which unfavorably hinders the dissolution with a (BiNa)Ti03 calcined powder to be mixed later The step of preparing a (BiNa)Ti03 calcined powder in the invention mcludes mixing Na2CO3, B12O3 and T1O2 as starting powders to prepare a mixed starting powder, followed by calcining the powder The calculation temperature is preferably in the range of from 700 to 950°C, and the calcination tune is preferably from 0 5 to 10 hours When the calcination temperature is lower than 700°C or the calcination tune is shorter than 0 5 hours, unreacted NaO may react with water m the atmosphere or in the solvent in wet mixing to unfavorably cause compositional deviation or characteristic fluctuation On the other hand, when the calcination temperature exceeds 950°C or the calcination tune is longer than 10 hours, then Bi may evaporate greatly to unfavorably cause compositional deviation and promote formation of different phases Incidentally, with respect to the preferred calcination temperature in the step of preparing the Ba(TiM)03 calcined powder (from 900 to 1300°C) and the preferred calcination temperature m the step of preparing the (BiNa)TiO3 calcmed powder (from 700 to 950°C), it is preferred to select optimal temperatures according to use and the like For example, for performmg sufficient reaction while restraimng the evaporation of Bi, the calcination temperature of (BiNa)Ti03 is preferably relatively low by the adjustment of the calcination time and the like It is preferred to set the calcination temperature of (BiNa)Ti03 lower than the calcination temperature of Ba(TiM)03 A mam feature of the invention is that the step of preparing the Ba(TiM)O3 calcined powder and the step of preparing the (BiNa)Ti03 calcmed powder are earned out separately, and accordingly, Bi is restrained from evaporating away from (BiNa)TiOj in the calcination step and the compositional deviation of Bi-Na is restrained to inhibit the formation of different phases, and the invention thus provides a semiconductor ceramic composition of which the resistivity at room temperature is further reduced and of which the Curie temperature is restrained from fluctuating In the steps of preparing the above-mentioned calcmed powders, the starting material powders may be crushed m mixing depending upon the gram sizes of the material powders Mixture and crushing may be performed by any of wet mixing and crushing using pure water and ethanol, and dry mixing and crushing, but dry mixing and crushing is preferred for the reason of capable of restraimng compositional deviation Further, BaCCh, Na2CO3 and T1O2 are exemplified as the starting materials in the above, but the advantage of the invention is not impaired even when other Ba compounds, Na compounds and the like are used As described above, after separately preparing a Ba(TiM)03 calcmed powder and a (BiNa)TiO3 calcined powder, the calcmed powders are mixed each in a prescnbed amount Mixing may be performed by any of wet mixing using pure water and ethanol, and dry mixing, but dry mixing is preferred for capable of restraining compositional deviation Dependmg upon the gram sizes of the calcined powders, crushing may be earned out after mixing, or mixing and crushing may be performed at the same time The average gram size of the mixed calcined powder after mixing and crushing is preferably from 0 6 to 1 5 urn In the above-mentioned step of preparing the Ba(TiM)03 calcined powder and/or the step of preparing the (BiNa)Ti03 calcined powder, or in the step of mixing the calcined powders, adding at most 3 0 mol% of Si oxide and at most 4 0 mol% of Ca oxide or Ca carbonate is favorable because Si oxide may restrain the abnormal growth of crystal grains and may readily control the resistivity of the composition, and Ca oxide or Ca carbonate may enhance the sinterability of the composition at low temperatures and may control the reducibility thereof However, when either one of them is added m an amount exceedmg the above-mentioned limit, then it is unfavorable since the composition cannot be semiconducnve Preferably, the addition is attained before mixing m each step A semiconductor ceramic composition according to the mvention can be obtained by forming and sintering the mixed calcined powder obtained in the step of mixing the Ba(TiM)03 calcined powder and the (BiNa)Ti03 calcined powder One example of a process after the step of mixing the calcined powders is described below, to which, however, the mvention should not be limited Any and every known method is employable m the mvention The mixed calcined powder obtained in the step of mixing a Ba(TiM)03 calcined powder and a (BiNa)Ti03 calcined powder may be formed by any desired forming means Before forming, if desired, the crushed powder may be granulated in a granulation apparatus The density of the compact after the forming is preferably from 2 to 3 g/cm3 The smtenng may be attained in air or in. a reducing atmosphere, or in an inert gas atmosphere having a low oxygen concentration, at a smtenng temperature of from 1200QC to 1400°C for a smtenng tune of from 2 hours to 6 hours One prefened embodiment of the smtenng step is descnbed below In case where the powder is granulated before forming, it is preferably processed for bmder removal at 300°C to 700°C before smtenng In the smtenng step at a smtenng temperature of from 1290°C to 1350°C m an atmosphere havmg an oxygen concentration of less than 1%, the powder is sintered (1) for a smtenng time of shorter than 4 hours, or (2) for a sintering time to satisfy a formula AT > 25t (t = sintering time (hr), AT = cooling rate (°C/hr) after smtenng), and then the sintered body is cooled at the coolmg rate satisfying the above formula. According to the smtenng step of any mode mentioned m the above, where the smtenng time is shortened, or the smtenng tune is kept long but the sintered body is rapidly cooled at a suitable rapid coolmg rate in accordance with the smtenng time, a semiconductor ceramic composition havmg an improved temperature coefficient of resistance m a high-temperature range (not lower than the Curie temperature) while mamtaimng a low resistivity at room temperature can be obtamed without the necessity of heat treatment m air like that for BaTi03 matenals In the above sintering step, the atmosphere having an oxygen atmosphere of less than 1% means a vacuum or an inert gas atmosphere havmg an oxygen atmosphere of less than 1 % Preferred is an inert gas atmosphere, for example, a nitrogen gas or argon gas atmosphere The atmosphere in coolmg after the smtenng is also preferably the above-mentioned atmosphere, but is not always limitative In case where the smtenng step mode is the above method (1), the cooling condition after the smtenng may be selected m any desired manner On the other hand, when the above method (2) is selected, the cooling rate At (°C/hr) is determined by the smtermg time t For example, when the sintering time t is 1 hour, then the cooling rate AT is 25 x 1 = 25°C/hr or more, and when the sintering tune t is 4 hours, then the cooling rate AT is 25 x 4 = 100°C/hr or more In other words, when the sintering time t is long, then the coolmg rate AT shall be higher m accordance with the sintering time This method may be effective when the smtermg time t is long, but is applicable to a shorter sintering tune t (for example, shorter than 4 hours) The semiconductor ceramic composition to which the invention is directed is BaTiO3 in which a part of Ba is substituted with Ba-Na. As so mentioned m the above, this is obtained according to a process including separately conducting the step of prepanng a calcmed Ba(TiM)O3 powder (M is a semiconductor dopant) and the step of prepanng a calcmed (BiNa)Ti03 powder, followed by mixing, formmg and smtermg The composition m which a part of BaTiO3 is substituted with Bi-Na is processed into a semiconductor ceramic composition by addmg a semiconductor dopant thereto, followed by valence control of the composition In the invention, the semiconductor dopant is added to BaTi03 to give a calcmed Ba(TiM)03 powder (M is semiconductor dopant), and the resulting semiconductor ceramic composition is represented by a composition formula [(BiNa)xBai-x][Tii ,My]O3 in which x and y each satisfy 0 In the composition represented by [(BiNa)xBai x][Tii yMy]O3, x represents the component range of (BiNa), and x is preferably in the range of 0 M is at least one of Nb and Sb, but is preferably Nb In the composition, y represents the component range of M, and y is preferably in the range of 0 In the above composition represented by [(BuMa)xBai.x][Ti\| yMy]O3, Ti is substituted with an element M for valence control In this case, the addition of the element M (the amount to be added, 0 In the above-mentioned composition represented by [(BiNa^Baj x][Tii yMy]O3, the ratio of Bi to Na is preferably 1/1, or that is, the composition formula is preferably [(Bio sNao 5)xBai J [Tii.yMy]O3 However, as so described in the section of the background art, when all the constituents are mixed before calcination, then Bi may vaporize in the calcination step to cause compositional deviation in Bi-Na, whereby the formation of different phases may be accelerated, and accompanied by the problems in that the resistivity at room temperature increases and the Curie temperature may fluctuate In the invention, by separately calcining a calcmed powder of Ba(TiM)03 and a calcmed powder of (BiNa)TiO3 composition respectively at optmal temperatures, the proportion of Bi to Na can be made to satisfy that Bi/Na is from 0 78 to 1, so that the resistivity at room temperature can be further lowered and the fluctuation in the Curie temperature can be restrained When Bi/Na is more than 1, then Bi not participating in the formation of (BiNa)Ti03 may remain m the matenal to readily form different phases in sintering, whereby the resistivity at room temperature may unfavorably increase, while when it is less than 0 78, then different phases may be readily formed m the sintering step and the resistivity at room temperature may unfavorably increase According to the above-mentioned production process, a semiconductor ceramic composition represented by a composition formula [(BiNa)xBai.x][Tii-yMy]O3 (wherein M is at least one of Nb and Sb), m which x and y each satisfy 0 EXAMPLES Example 1 BaCO3 and T1O2 as mam materials and Nb2O5 as a semiconductor ingredient powder were prepared and blended so as to be Ba(Tio wsNbo 002)O3, followed by mixing in pure water The obtained mixed matenal powder was calcined at 1000°C for 4 hours to prepare a Ba(TiNb)O3 calcined powder Na2CO3, Bi2O3 and T1O2 as matenal powders were prepared and blended so as to be (Bio 5Nao 5)TiO3) followed by mixing in ethanol The obtained mixed matenal powder was calcined in air at 600°C to 900°C for 4 hours to prepare a (BiNa)Ti03 calcined powder Fig 1 shows the X-ray diffraction patterns of the obtained (Bio sNao 5)TiO3 calcined powder at different calcination temperatures of from 600°C to 900°C The Ba(TiNb)03 calcmed powder and the (BiNa)Ti03 calcmed powder calcmed at 800°C were blended so as to be 73/7 m a molar ratio, then 0 4 mol% of S1O2 and 1 4 mol% of CaCO3 were added thereto as sintering promoters, and these were mixed and crushed in a pot mill with pure water as a medium until the mixed calcmed powder had a center grain size of from 1 0 uxn to 2 0 urn, and then dried PVA was added to the crushed powder of the mixed calcmed powder, followed by mixing, and the mixture was granulated with a granulator The granulated powder thus obtained was formed with a uniaxial pressing machine, the compact was processed for binder removal at 500°C, and then sintered in air at a sintering temperature of from 1300°C to 1380°C for 4 hours to give a sintered body A test piece was obtained by processing the obtained sintered body into a plate havmg a size of 10 mm x 10 mm x1 ram, with which an ohmic electrode was formed The test piece was tested with a resistance meter to determine its resistivity change m a temperature range from room temperature to 270°C The measurement results are shown in Table 1 The test piece was analyzed for the constitutive elements Bi and Na, and the ratio of Bi/Na was determined The results are shown m Table 1 In producmg Sample No 5 in Table 1, the powders were mixed in dry in air in the step of preparing the calcmed (BiNa)TiO3 powder, and except this, the mgredients were mixed in ethanol The sample numbered with * is Comparative Example Comparative Example 1 BaCO3 and T1O2 as main materials, NbiO5 as a semiconductor ingredient powder, and Na2CO3, B12O3 and T1O2 as Curie temperature shifters were prepared, and all these constituents were mixed all at a time from the beginning, and further, 0 9 mol% of S1O2 and 1 9 mol% of CaCO3 were added thereto as sintering promoters, and these were mixed in ethanol The mixed material powder thus obtained was calcined in air at 200°C to 1200°C for 4 hours to give a calcined powder Fig 2 shows the X-ray diffraction patterns of the obtained [(Bio sNao s)xBai.x][Tii yMy]O3 calcined powder (x = 0 06, y = 0 005) at different calcination temperatures of from 200°C to 900°C PVA was added to the powder calcined at 1000°C, followed by mixing, and the mixture was granulated with a granulator The granulated powder thus obtained was formed with a uniaxial pressmg machine, the compact was processed for binder removal at 500°C, and then sintered in air at a sintering temperature of 1320°C for 4 hours to give a sintered body A test piece was obtained by processing the obtained sintered body into a plate having a size of 10 mm x 10 mm x 1 mm, with which an ohmic electrode was formed The test piece was tested with a resistance meter to determine its resistivity change in a temperature range from room temperature to 270°C The measurement results are shown in Table 1 as Sample No 6 The test piece was analyzed for the constitutive elements Bi and Na, and the ratio of Bi/Na was determined The result is shown m Table 1 as Sample No 6 As can be clearly seen from Fig 1 and Fig 2, the calcined (BiNa)Ti03 powder in Example 1 formed a completely single phase at 700°C On the other hand, it is shown that, in Comparative Example 1 in which all the constitutive elements were mixed all at a time from the beginning, complete dissolution could not be attained until the temperature becomes not lower than 900°C, and it was not sufficient as a calcined powder As can be clearly seen from Table 1, the semiconductor ceramic compositions accordmg to the mvention have an mcreased Cune temperature and have a significantly reduced resistivity at room temperature Since the step of preparing the Ba(TiNb)03 calcined powder and the step of preparing the (BiNa)Ti03 calcined powder were conducted separately, Bi was restrained from vaporizing, and even after sintered, the composition could have a high Bi/Na ratio, and therefore, the formation of different phases was restrained mthe composition, and the resistivity at room temperature was further lowered and the Curie temperature fluctuation was restrained As opposed to this, the temperature coefficient of resistance of the semiconductor ceramic composition of Comparative Example was low though the Cune temperature thereof was elevated In addition, in the calcination step and m the sintering step, much Bi vaporized away, and the Bi/Na ratio in the sintered body was 0 77 or lower In all Examples, the temperature coefficient of resistance was calculated according to the following formula TCR = (lnRrlnJQ x 100/(T,-TC) wherein. Ri means the maximum resistivity, Re means the resistivity at T0, Ti means the temperature at which the composition has Ri, and Tc means the Cune temperature (Table Removed) Table 1 While the invention has been described m detail and with reference to specific embodiments thereof, it will be apparent to one skilled m the art that various changes and modifications can be made therem without departmg from the spirit and scope thereof The present application is based on Japanese Patent Application No 2006-298304 filed on November 1,2006, and the contents are incorporated herein by reference INDUSTRIAL APPLICABILITY The semiconductor ceramic composition according to the invention is optimal as a matenal for a PTC thermistor, a PTC heater, a PTC switch, a temperature detector, and the like We Claim:- 1. A process for producing a semiconductor ceramic composition in which a part of Ba in BaTiO3 is substituted with Bi-Na, the process comprising a step of preparing a calcined powder of Ba(TiM)O3 (wherein M is a semiconductor dopant), a step of preparing a calcined powder of (BiNa)TiO3, a step of mixing the calcined powder of Ba(TiM)O3 and the calcined powder of (BiNa)TiO3, and a step of forming and sintering the mixed calcined powder. 2. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein a calcination temperature in the step of preparing the calcined powder of Ba(TiM)O3 is fiom 900 to 1300°C. 3. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein a calcination temperature in the step of preparing the calcined powder of (BiNa)TiO3 is from 700 to 950°C. 4. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein a dry mixing is conducted in the step of mixing the calcined powder of Ba(TiM)O3 and the calcined powder of (BiNa)TiO3. 5. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein 3.0 mol% or less of Si oxide and 4.0 mol% or less of Ca carbonate or Ca oxide are added before the calcination in the step of preparing the calcined powder of Ba(TiM)O3 or the step of preparing the calcined powder of (BiNa)TiO3 or in both the two steps. 6. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein 3.0 mol% or less of Si oxide and 4.0 mol% or less of Ca carbonate or Ca oxide are added in the step of mixing the calcined powder of Ba(TiM)O3 and the calcined powder of (BiNa)TiO3. 7. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein the semiconductor dopant M is at least one of Nb and Sb, and the semiconductor ceramic composition is represented by a composition formula: [(BiNa)xBai.x3[Ti1-yMy]O3 in which x and y each satisfy 0 8. The process for producing a semiconductor ceramic composition as claimed in claim 7, wherein a ratio of Bi to Na satisfies a relationship that Bi/Na is 0.78 to 1. 9. A semiconductor ceramic composition obtained by forming and sintering a mixed calcined powder containing a calcined powder of Ba(TiM)Oa (wherein M is a semiconductor dopant and is at least one of Nb and Sb) and a calcined powder of (BiNa)TiO3, wherein the composition is represented by a composition formula: [(BINa)Bai-x][Ti1-yMy]O3 in which x and y each satisfy 0

Full Text

DESCRIPTION
TECHNICAL FIELD
The present invention relates to a semiconductor ceramic composition having a positive resistive temperature, which is used for a PTC thermistor, a PTC heater, a PTC switch, a temperature detector and the like, and a process for producing the same.
BACKGROUND ART
As materials showing a PTCR characteristic (Positive Temperature Coefficient of Resistivity), compositions in which various semiconductor dopants are added to BaTiO3 have been conventionally proposed. These compositions have a Curie temperature around 120°C. Depending upon the use, it becomes necessary for these compositions to shift the Curie temperature thereof.
It has been proposed to shift the Curie temperature by adding, for example, SrTiCh to BaTiO3. However, the Curie temperature shifts only to a negative direction and does not shift to a positive direction in this case. Currently, only PbTiOa is known as an additive material for shifting the Curie temperature to a positive direction. However, since PbTiOs contains an element that causes environmental pollution, a material using no PbTiO3 has been demanded in recent years.
Regarding BaTiO3 semiconductor ceramics, there is proposed a process for producing a BaTiO3 semiconductor ceramic by adding one or more of Nb, Ta and rare earth elements to a composition having a structure of Baj.(BiNa)TiOa, wherein a part
of Ba m BaTiO3 m which no PbTiO3 is used is substituted with Bi-Na and x is controlled to be in a range of 0 Patent Document 1 JP-A-56-169301
DISCLOSURE OF THE INVENTION
PROBLEMS THAT THE INVENTION IS TO SOLVE Patent Document 1 discloses m Examples, mixing, before calcination thereof, all the constituents such as the starting matenals including BaCO3, T1O2, B12O3, Na203 and PbO, followed by calcining, forming, sintering and heat-treating
However, m the composition where a part of Ba of BaTiO3 is substituted with Bi-Na, when all the constituents are mixed before calcination thereof as in Patent Document 1, men Bi may evaporate during the calcination step to cause compositional deviation m Bi-Na, whereby the formation of different phases is accelerated, and increase in the resistivity at room temperature and fluctuation of the Curie temperature may be caused
It may be considered to perform calcination at a low temperature for restraining the evaporation of Bi However, although the evaporation of Bi is certainly restrained by this method, a complete solid solution cannot be formed and the desired characteristics cannot be obtained
An object of the invention is to provide a semiconductor ceramic composition containing no Pb, which is capable of shifting the Cune temperate to a positive direction and of widely reducing the resistivity at room temperature, and to provide a production process of the same
Further, it is another object of the invention to provide a semiconductor ceramic composition m which a part of Ba m BaTiCh is substituted with Bi-Na, which is capable of restraining the evaporation of Bi in the calcination step, is capable of restraining the compositional deviation of Bi-Na thereby suppressing the formation of different phases, is capable of further reducing the resistivity at room temperature, and is capable of restraining the fluctuation of the Cune temperature, and to provide a production process of the same
MEANS FOR SOLVING THE PROBLEMS
As a result of intensive studies for attaining the above objects, the inventors have found that, in producing a semiconductor ceramic composition m which a part of Ba m BaTi03 is substituted with Bi-Na, when a calcined Ba(TiM)03 powder (M is a semiconductor dopant) and a calcined (BaNa)Ti03 powder are separately prepared and the Ba(TiM)03 powder is calcmed at a relatively high temperature while the (BaNa)Ti03 powder is calcmed at a relatively low temperature, both at the most suitable temperatures for them, then the evaporation of Bi from the calcmed Ba(TiM)03 powder may be retarded and the compositional deviation of Bi-Na may be thereby suppressed to inhibit the formation of different phases, and when these calcmed powders are mixed, formed and sintered, then a semiconductor ceramic composition which has a low resistivity at room temperature and is capable of restraining the fluctuation of the Cune temperature can be obtained
The invention provides a process for producing a semiconductor ceramic composition m which a part of Ba of BaTiO3 is substituted with Bi-Na, the process comprising a step of prepanng a calcined powder of Ba(TiM)03 (wherein M is a semiconductor dopant), a step of prepanng a calcined powder of (BiNa)Ti03, a step of mixing the calcined powder of Ba(TiM)03 and the calcined powder of (BiNa)Ti03, and a step of forming and sintering the mixed calcined powder
The invention further proposes, in the production process of the above-mentioned constitution
a constitution in which a calcination temperature in the step of prepanng the calcined powder of Ba(TiM)03 is from 900 to 1300°C,
a constitution m which a calcination temperature in the step of prepanng the calcined powder of (B£Na)Ti03 is from 700 to 950°C,
a constitution in which a dry mixing is conducted m the step of mixing the calcined powder of Ba(TiM)03 and the calcined powder of (BiNa)Ti03,
a constitution in which 3 0 mol% or less of Si oxide and 4 0 mol% or less of Ca carbonate or Ca oxide are added before the calcination in the step of prepanng the calcined powder of Ba(TiM)03 or the step of prepanng the calcined powder of (BiNa)Ti03 or in both the two steps,
a constitution in which 3 0 mol% or less of Si oxide and 4 0 mol% or less of Ca carbonate or Ca oxide are added in the step of mixing the calcined powder of Ba(TiM)03 and the calcined powder of (BiNa)Ti03,
a constitution m which the semiconductor dopant M is at least one of Nb and Sb, and the semiconductor ceramic composition is represented by a composition formula [(BiNa)Bai-]fTii-yMy]O3 in which x and y each satisfy 0 a constitution m which the ratio of Bi to Na satisfies a relationship that Bi/Na is 0 78 to 1
The invention also provides a semiconductor ceramic composition obtained by forming and sintering a mixed calcined powder containing a calcined powder of Ba(TiM)03 (wherein M is a semiconductor dopant and is at least one of Nb and Sb) and a calcined powder of (BiNa)Ti03, wherein the composition is represented by a composition formula [(BiNa)xBai-x][Tii-yMy]O3 m which x and y each satisfy 0 ADVANTAGE OF THE INVENTION
According to the invention, there can be provided a semiconductor ceramic composition capable of rising the Cune temperature and capable of greatly reducing the resistivity at room temperature without using Pb that causes environmental pollution
According to the invention, there can be provided a semiconductor ceramic composition capable of restraining the evaporation of Bi in the calcination step, capable of restraining the compositional deviation in Bi-Na to thereby inhibit the formation of different phases, capable of further reducing the resistivity at room temperature, and capable of restraining the fluctuation of the Cune temperature
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 is a graph showing the X-ray diffraction patterns of a semiconductor ceramic composition of the invention at different calcination temperatures
Fig 2 is a graph showing the X-ray diffraction patterns of a semiconductor ceramic composition of Comparative Example at different calcination temperatures
BEST MODE FOR CARRYING OUT THE INVENTION
In the step of preparing a calcined powder of Ba(TiM)O3 (M is a semiconductor dopant) in the invention, first, BaCO3 and T1O2 as mam starting materials and ND2O5 or SO2O3 as a semiconductor ingredient are mixed to prepare a mixed starting powder, and then the powder is calcined The calcination temperature is preferably m the range of from 900 to 1300°C, and the calcination time is preferably 0 5 hours or more When the calcination temperature is lower than 900°C or the calculation time is shorter than 0 5 hours, Ba(TiM)03 is not completely formed, and the unreacted BaO may react with water in the atmosphere or in the mixed medium to unfavorably cause compositional deviation On the other hand, when the calcination temperature exceeds 1300°C, then a sintered body is generated in the calcined powder, which unfavorably hinders the dissolution with a (BiNa)Ti03 calcined powder to be mixed later
The step of preparing a (BiNa)Ti03 calcined powder in the invention mcludes mixing Na2CO3, B12O3 and T1O2 as starting powders to prepare a mixed starting powder, followed by calcining the powder The calculation temperature is preferably in the range of from 700 to 950°C, and the calcination tune is preferably from 0 5 to 10 hours When the calcination temperature is lower than 700°C or the calcination tune is shorter than 0 5 hours, unreacted NaO may react with water m the atmosphere or in the solvent in wet mixing to unfavorably cause compositional deviation or characteristic fluctuation On the other hand, when the calcination temperature exceeds 950°C or the calcination tune is longer than 10 hours, then Bi may evaporate greatly to unfavorably cause compositional deviation and promote formation of different phases
Incidentally, with respect to the preferred calcination temperature in the step of preparing the Ba(TiM)03 calcined powder (from 900 to 1300°C) and the preferred
calcination temperature m the step of preparing the (BiNa)TiO3 calcmed powder (from 700 to 950°C), it is preferred to select optimal temperatures according to use and the like For example, for performmg sufficient reaction while restraimng the evaporation of Bi, the calcination temperature of (BiNa)Ti03 is preferably relatively low by the adjustment of the calcination time and the like It is preferred to set the calcination temperature of (BiNa)Ti03 lower than the calcination temperature of Ba(TiM)03
A mam feature of the invention is that the step of preparing the Ba(TiM)O3 calcined powder and the step of preparing the (BiNa)Ti03 calcmed powder are earned out separately, and accordingly, Bi is restrained from evaporating away from (BiNa)TiOj in the calcination step and the compositional deviation of Bi-Na is restrained to inhibit the formation of different phases, and the invention thus provides a semiconductor ceramic composition of which the resistivity at room temperature is further reduced and of which the Curie temperature is restrained from fluctuating
In the steps of preparing the above-mentioned calcmed powders, the starting material powders may be crushed m mixing depending upon the gram sizes of the material powders Mixture and crushing may be performed by any of wet mixing and crushing using pure water and ethanol, and dry mixing and crushing, but dry mixing and crushing is preferred for the reason of capable of restraimng compositional deviation Further, BaCCh, Na2CO3 and T1O2 are exemplified as the starting materials in the above, but the advantage of the invention is not impaired even when other Ba compounds, Na compounds and the like are used
As described above, after separately preparing a Ba(TiM)03 calcmed powder and a (BiNa)TiO3 calcined powder, the calcmed powders are mixed each in a prescnbed amount Mixing may be performed by any of wet mixing using pure water and ethanol, and dry mixing, but dry mixing is preferred for capable of restraining
compositional deviation Dependmg upon the gram sizes of the calcined powders, crushing may be earned out after mixing, or mixing and crushing may be performed at the same time The average gram size of the mixed calcined powder after mixing and crushing is preferably from 0 6 to 1 5 urn
In the above-mentioned step of preparing the Ba(TiM)03 calcined powder and/or the step of preparing the (BiNa)Ti03 calcined powder, or in the step of mixing the calcined powders, adding at most 3 0 mol% of Si oxide and at most 4 0 mol% of Ca oxide or Ca carbonate is favorable because Si oxide may restrain the abnormal growth of crystal grains and may readily control the resistivity of the composition, and Ca oxide or Ca carbonate may enhance the sinterability of the composition at low temperatures and may control the reducibility thereof However, when either one of them is added m an amount exceedmg the above-mentioned limit, then it is unfavorable since the composition cannot be semiconducnve Preferably, the addition is attained before mixing m each step
A semiconductor ceramic composition according to the mvention can be obtained by forming and sintering the mixed calcined powder obtained in the step of mixing the Ba(TiM)03 calcined powder and the (BiNa)Ti03 calcined powder One example of a process after the step of mixing the calcined powders is described below, to which, however, the mvention should not be limited Any and every known method is employable m the mvention
The mixed calcined powder obtained in the step of mixing a Ba(TiM)03 calcined powder and a (BiNa)Ti03 calcined powder may be formed by any desired forming means Before forming, if desired, the crushed powder may be granulated in a granulation apparatus The density of the compact after the forming is preferably from 2 to 3 g/cm3
The smtenng may be attained in air or in. a reducing atmosphere, or in an inert gas atmosphere having a low oxygen concentration, at a smtenng temperature of from 1200QC to 1400°C for a smtenng tune of from 2 hours to 6 hours One prefened embodiment of the smtenng step is descnbed below In case where the powder is granulated before forming, it is preferably processed for bmder removal at 300°C to 700°C before smtenng
In the smtenng step at a smtenng temperature of from 1290°C to 1350°C m an atmosphere havmg an oxygen concentration of less than 1%, the powder is sintered (1) for a smtenng time of shorter than 4 hours, or (2) for a sintering time to satisfy a formula AT > 25t (t = sintering time (hr), AT = cooling rate (°C/hr) after smtenng), and then the sintered body is cooled at the coolmg rate satisfying the above formula.
According to the smtenng step of any mode mentioned m the above, where the smtenng time is shortened, or the smtenng tune is kept long but the sintered body is rapidly cooled at a suitable rapid coolmg rate in accordance with the smtenng time, a semiconductor ceramic composition havmg an improved temperature coefficient of resistance m a high-temperature range (not lower than the Curie temperature) while mamtaimng a low resistivity at room temperature can be obtamed without the necessity of heat treatment m air like that for BaTi03 matenals
In the above sintering step, the atmosphere having an oxygen atmosphere of less than 1% means a vacuum or an inert gas atmosphere havmg an oxygen atmosphere of less than 1 % Preferred is an inert gas atmosphere, for example, a nitrogen gas or argon gas atmosphere The atmosphere in coolmg after the smtenng is also preferably the above-mentioned atmosphere, but is not always limitative
In case where the smtenng step mode is the above method (1), the cooling condition after the smtenng may be selected m any desired manner On the other
hand, when the above method (2) is selected, the cooling rate At (°C/hr) is determined by the smtermg time t For example, when the sintering time t is 1 hour, then the cooling rate AT is 25 x 1 = 25°C/hr or more, and when the sintering tune t is 4 hours, then the cooling rate AT is 25 x 4 = 100°C/hr or more In other words, when the sintering time t is long, then the coolmg rate AT shall be higher m accordance with the sintering time This method may be effective when the smtermg time t is long, but is applicable to a shorter sintering tune t (for example, shorter than 4 hours)
The semiconductor ceramic composition to which the invention is directed is BaTiO3 in which a part of Ba is substituted with Ba-Na. As so mentioned m the above, this is obtained according to a process including separately conducting the step of prepanng a calcmed Ba(TiM)O3 powder (M is a semiconductor dopant) and the step of prepanng a calcmed (BiNa)Ti03 powder, followed by mixing, formmg and smtermg
The composition m which a part of BaTiO3 is substituted with Bi-Na is processed into a semiconductor ceramic composition by addmg a semiconductor dopant thereto, followed by valence control of the composition In the invention, the semiconductor dopant is added to BaTi03 to give a calcmed Ba(TiM)03 powder (M is semiconductor dopant), and the resulting semiconductor ceramic composition is represented by a composition formula [(BiNa)xBai-x][Tii ,My]O3 in which x and y each satisfy 0 In the composition represented by [(BiNa)xBai x][Tii yMy]O3, x represents the component range of (BiNa), and x is preferably in the range of 0 M is at least one of Nb and Sb, but is preferably Nb In the composition, y represents the component range of M, and y is preferably in the range of 0 In the above composition represented by [(BuMa)xBai.x][Ti| yMy]O3, Ti is substituted with an element M for valence control In this case, the addition of the element M (the amount to be added, 0 In the above-mentioned composition represented by [(BiNa^Baj x][Tii yMy]O3, the ratio of Bi to Na is preferably 1/1, or that is, the composition formula is preferably [(Bio sNao 5)xBai J [Tii.yMy]O3 However, as so described in the section of the background art, when all the constituents are mixed before calcination, then Bi may vaporize in the calcination step to cause compositional deviation in Bi-Na, whereby the formation of different phases may be accelerated, and accompanied by the problems in that the resistivity at room temperature increases and the Curie temperature may fluctuate
In the invention, by separately calcining a calcmed powder of Ba(TiM)03 and a calcmed powder of (BiNa)TiO3 composition respectively at optmal temperatures, the proportion of Bi to Na can be made to satisfy that Bi/Na is from 0 78 to 1, so that the resistivity at room temperature can be further lowered and the fluctuation in the Curie temperature can be restrained When Bi/Na is more than 1, then Bi not participating in
the formation of (BiNa)Ti03 may remain m the matenal to readily form different phases in sintering, whereby the resistivity at room temperature may unfavorably increase, while when it is less than 0 78, then different phases may be readily formed m the sintering step and the resistivity at room temperature may unfavorably increase
According to the above-mentioned production process, a semiconductor ceramic composition represented by a composition formula [(BiNa)xBai.x][Tii-yMy]O3 (wherein M is at least one of Nb and Sb), m which x and y each satisfy 0 EXAMPLES
Example 1
BaCO3 and T1O2 as mam materials and Nb2O5 as a semiconductor ingredient powder were prepared and blended so as to be Ba(Tio wsNbo 002)O3, followed by mixing in pure water The obtained mixed matenal powder was calcined at 1000°C for 4 hours to prepare a Ba(TiNb)O3 calcined powder
Na2CO3, Bi2O3 and T1O2 as matenal powders were prepared and blended so as to be (Bio 5Nao 5)TiO3) followed by mixing in ethanol The obtained mixed matenal powder was calcined in air at 600°C to 900°C for 4 hours to prepare a (BiNa)Ti03 calcined powder Fig 1 shows the X-ray diffraction patterns of the obtained (Bio sNao 5)TiO3 calcined powder at different calcination temperatures of from 600°C to 900°C
The Ba(TiNb)03 calcmed powder and the (BiNa)Ti03 calcmed powder calcmed at 800°C were blended so as to be 73/7 m a molar ratio, then 0 4 mol% of S1O2 and 1 4 mol% of CaCO3 were added thereto as sintering promoters, and these were mixed and crushed in a pot mill with pure water as a medium until the mixed calcmed powder had a center grain size of from 1 0 uxn to 2 0 urn, and then dried PVA was added to the crushed powder of the mixed calcmed powder, followed by mixing, and the mixture was granulated with a granulator The granulated powder thus obtained was formed with a uniaxial pressing machine, the compact was processed for binder removal at 500°C, and then sintered in air at a sintering temperature of from 1300°C to 1380°C for 4 hours to give a sintered body
A test piece was obtained by processing the obtained sintered body into a plate havmg a size of 10 mm x 10 mm x1 ram, with which an ohmic electrode was formed The test piece was tested with a resistance meter to determine its resistivity change m a temperature range from room temperature to 270°C The measurement results are shown in Table 1 The test piece was analyzed for the constitutive elements Bi and Na, and the ratio of Bi/Na was determined The results are shown m Table 1 In producmg Sample No 5 in Table 1, the powders were mixed in dry in air in the step of preparing the calcmed (BiNa)TiO3 powder, and except this, the mgredients were mixed in ethanol The sample numbered with * is Comparative Example
Comparative Example 1
BaCO3 and T1O2 as main materials, NbiO5 as a semiconductor ingredient powder, and Na2CO3, B12O3 and T1O2 as Curie temperature shifters were prepared, and all these constituents were mixed all at a time from the beginning, and further, 0 9

mol% of S1O2 and 1 9 mol% of CaCO3 were added thereto as sintering promoters, and these were mixed in ethanol The mixed material powder thus obtained was calcined in air at 200°C to 1200°C for 4 hours to give a calcined powder Fig 2 shows the X-ray diffraction patterns of the obtained [(Bio sNao s)xBai.x][Tii yMy]O3 calcined powder (x = 0 06, y = 0 005) at different calcination temperatures of from 200°C to 900°C
PVA was added to the powder calcined at 1000°C, followed by mixing, and the mixture was granulated with a granulator The granulated powder thus obtained was formed with a uniaxial pressmg machine, the compact was processed for binder removal at 500°C, and then sintered in air at a sintering temperature of 1320°C for 4 hours to give a sintered body
A test piece was obtained by processing the obtained sintered body into a plate having a size of 10 mm x 10 mm x 1 mm, with which an ohmic electrode was formed The test piece was tested with a resistance meter to determine its resistivity change in a temperature range from room temperature to 270°C The measurement results are shown in Table 1 as Sample No 6 The test piece was analyzed for the constitutive elements Bi and Na, and the ratio of Bi/Na was determined The result is shown m Table 1 as Sample No 6
As can be clearly seen from Fig 1 and Fig 2, the calcined (BiNa)Ti03 powder in Example 1 formed a completely single phase at 700°C On the other hand, it is shown that, in Comparative Example 1 in which all the constitutive elements were mixed all at a time from the beginning, complete dissolution could not be attained until the temperature becomes not lower than 900°C, and it was not sufficient as a calcined powder
As can be clearly seen from Table 1, the semiconductor ceramic compositions accordmg to the mvention have an mcreased Cune temperature and have a significantly
reduced resistivity at room temperature Since the step of preparing the Ba(TiNb)03 calcined powder and the step of preparing the (BiNa)Ti03 calcined powder were conducted separately, Bi was restrained from vaporizing, and even after sintered, the composition could have a high Bi/Na ratio, and therefore, the formation of different phases was restrained mthe composition, and the resistivity at room temperature was further lowered and the Curie temperature fluctuation was restrained
As opposed to this, the temperature coefficient of resistance of the semiconductor ceramic composition of Comparative Example was low though the Cune temperature thereof was elevated In addition, in the calcination step and m the sintering step, much Bi vaporized away, and the Bi/Na ratio in the sintered body was 0 77 or lower
In all Examples, the temperature coefficient of resistance was calculated according to the following formula
TCR = (lnRrlnJQ x 100/(T,-TC) wherein. Ri means the maximum resistivity, Re means the resistivity at T0, Ti means the temperature at which the composition has Ri, and Tc means the Cune temperature
(Table Removed)
Table 1
While the invention has been described m detail and with reference to specific embodiments thereof, it will be apparent to one skilled m the art that various changes and modifications can be made therem without departmg from the spirit and scope thereof
The present application is based on Japanese Patent Application No 2006-298304 filed on November 1,2006, and the contents are incorporated herein by
reference
INDUSTRIAL APPLICABILITY
The semiconductor ceramic composition according to the invention is optimal as a matenal for a PTC thermistor, a PTC heater, a PTC switch, a temperature detector, and the like

We Claim:-
1. A process for producing a semiconductor ceramic composition in which a part of Ba in BaTiO3 is substituted with Bi-Na, the process comprising a step of preparing a calcined powder of Ba(TiM)O3 (wherein M is a semiconductor dopant), a step of preparing a calcined powder of (BiNa)TiO3, a step of mixing the calcined powder of Ba(TiM)O3 and the calcined powder of (BiNa)TiO3, and a step of forming and sintering the mixed calcined powder.
2. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein a calcination temperature in the step of preparing the calcined powder of Ba(TiM)O3 is fiom 900 to 1300°C.
3. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein a calcination temperature in the step of preparing the calcined powder of (BiNa)TiO3 is from 700 to 950°C.
4. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein a dry mixing is conducted in the step of mixing the calcined powder of Ba(TiM)O3 and the calcined powder of (BiNa)TiO3.
5. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein 3.0 mol% or less of Si oxide and 4.0 mol% or less of Ca carbonate or Ca oxide are added before the calcination in the step of preparing the calcined powder
of Ba(TiM)O3 or the step of preparing the calcined powder of (BiNa)TiO3 or in both the two steps.
6. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein 3.0 mol% or less of Si oxide and 4.0 mol% or less of Ca carbonate or Ca oxide are added in the step of mixing the calcined powder of Ba(TiM)O3 and the calcined powder of (BiNa)TiO3.
7. The process for producing a semiconductor ceramic composition as claimed in claim 1, wherein the semiconductor dopant M is at least one of Nb and Sb, and the semiconductor ceramic composition is represented by a composition formula: [(BiNa)xBai.x3[Ti1-yMy]O3 in which x and y each satisfy 0 8. The process for producing a semiconductor ceramic composition as claimed in claim 7, wherein a ratio of Bi to Na satisfies a relationship that Bi/Na is 0.78 to 1.
9. A semiconductor ceramic composition obtained by forming and sintering a mixed calcined powder containing a calcined powder of Ba(TiM)Oa (wherein M is a semiconductor dopant and is at least one of Nb and Sb) and a calcined powder of (BiNa)TiO3, wherein the composition is represented by a composition formula: [(BINa)Bai-x][Ti1-yMy]O3 in which x and y each satisfy 0

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Patent Number

269025

Indian Patent Application Number

2479/DELNP/2009

PG Journal Number

40/2015

Publication Date

02-Oct-2015

Grant Date

29-Sep-2015

Date of Filing

16-Apr-2009

Name of Patentee

HITACHI METALS, LTD.

Applicant Address

2-1, SHIBAURA 1-CHOME, MINATO-KU, TOKYO 105-8614 (JP).

Inventors:

#	Inventor's Name	Inventor's Address
1	TOJI, KAZUYA	C/O YAMAZAKI WORKS, HITACHI METALS, LTD., 15-17, EGAWA 2-CHOME,SHIMAMOTO-CHO, MISHIMA-GUN, OSAKA 618-0013 (JP).
2	SHIMADA, TAKESHI	C/O ADVANCED ELECTRONICS RESEARCH LABORATORY, HITACHI METALS, LTD., 5200 MIKAJIRI, KUMAGAYA-SHI, SAITAMA 360-0843 (JP).

PCT International Classification Number

C04B 35/46

PCT International Application Number

PCT/JP2007/070958

PCT International Filing date

2007-10-26

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2006/298304	2006-11-01	Japan