Title of Invention	"A PROCESS FOR PREPARATION OF FERROELECTRIC LEAD MAGNESIUM NIOBATE-LEAD TITANATE (PMN-PT) CERAMICS"
Abstract	The present invention provides the method for the preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramic solid solution system free from pyrochlore phase and having high dielectric and piezoelectric properties and enhancing the reactivity of the constituents to achieve chemical homogeneity and stoichiometry in the sintered ceramics.

Full Text

A PROCESS FOR SYNTHESIS OF PMN-PT PIEZOELECTRIC AND ELECTROSTRICTIVE CERAMICS FREE FROM DETRIMENTAL PYROCHLORE PHASE FOR SMART SENSORS AND ACTUATORS Field of invention The present invention relates to a process for the preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramic solid solution system free from pyrochlore phase for applications such as actuators, multilayer capacitors, smart transducers, deformable mirrors and micropositioners Background and prior art Ferroelectric Lead Magnesium Niobate - Lead Titanate solid solutions (1-x) [Pb(Mg1/3 Nb2/3 )O3] x PbTiO3 abbreviated as PMN-PT are the most attractive material for multilayer ceramic capacitors, sensors, actuators and electromechanical transducers because of their excellent dielectric, piezoelectric properties and large electrostnctive strains However, it is very difficult to synthesize the PMN-PT powder free of parasitic pyrochlore phase (PD3ND4O13) which is extremely detrimental to the properties of PMN-PT Conventional mixed oxide route where oxides of all the constituents (viz MgO, PbO, Nb2O5 and T1O2) are mixed, calcined at elevated temperatures for solid solution formation, results in large amounts of pyrochlore phase due to inhomogemties in the composition and hence vastly varying from the required stoichiometry (A Mergen and WE Lee J European Ceram Soc 17, 1033, 1997) Use of excess MgO and PbO resulted in pyrochlore phase free PMN-PT powders but with inferior dielectric and piezoelectric properties (J Kelly et al, J Am Ceram Soc 80, 957, 1997) Columbite precursor method (S L Swartz and T R Shrout Mater Res Bull 17, 1245 1982) was able to reduce the pyrochlore phase Elimination of pyrochlore phase is not possible even after incorporating suitable intermediate process modifications (J P Guha et al J Am Ceram Soc 71, 152, 1988) However, the success of this approach depends on various process parameters, such as the reactivity of MgO, mixing control of PbO evaporation and the reversibility of the reaction (A Mergen and W E Lee J European Ceram Soc 17, 1033, 1997). (1-x) [Pb (Mg1/3 Nb2/3)O3] x PbTi03 is an attractive material with electromechanical properties better than those of well known and extensively used PZT-system PMN has been widely investigated due to large e and a transition temperature near room temperature (1-x) PMN- xPT (X ~ 0 10) has maximum dielectnc constant at room temperature It exhibits strong electrostnctive behavior so that field induced strain of greater than 0 1% can be obtained (S M Gupta and A R Kulkarm, Mat Res Bull 28, 1295, 1993) It is reported that the morphotropic phase boundary (MPB) exists at x ~ 0 30 -0 40 at which the electromechanical response of PMN-PT is maximum and much higher than PZT The other composition of PMN-PT at x ~ 0 10 has very high room temperature dielectric constant and electrostnctive coefficient resulting in high displacement values for actuator applications The effective piezocoefficient can be turned by changing the magnitude of DC bias field These features are highly desirable for actuators used in precise micropositioning and application in smart structure and MEMS devices The above two composition of PMN-PT system provide useful materials for actuator applications Due to high dielectnc, piezoelectric eletrostnctive and electro-optic coefficient-free from hysteresis PMN-PT is highly sought after matenal for actuators, multilayer capacitors, optical switches, wave guide modulator where high speed and efficiency are required However, the industrial applications of PMN-PT are limited due to non-availability of reproducible controlled processing techniques for achieving phase pure perovskite structure The conventional processes invariably lead to formation of unwanted pyrochlore phase, non-stoichiometry, inhomogeneity and inactive phases PMN-PT is very difficult to synthesise free from the unwanted pyrochlore phase, which is extremely detrimental to desired properties The pyrochlore phase is preferentially formed in PMN because PbO reacts with Nb2O5 at lower temperature (A Mergen and WE Lee J European Ceram Soc 17,1033,1997) The attempt of subsequent conversion of pyrochlore phase to perovskite phase has met with limited success due to slow and incomplete reaction for this transformation(s) Several attempts have also been made to prepare perovskite phase PMN by most adopted Columbite phase route in which first columnite phase (MgNb2O6 ) is developed and then reacted with PbO to form PMN - Goao has reported 12% pyrochlore phase by this method Chen and Shrout have investigated that pyrochlore phase is deficient in Mg2+ and Pb2+ and rich in Nb5+ and suggested that the formation of pyrochlore phase can be suppressed by removing Mg2+ and Pb2+ deficiency by their excess addition (T R Shrout and A Halliyal, Am Ceram Soc Bull 17, 1987) This technique however has a drawback that it leads to disturbance in stoichiometry and presence of excess inactive phase leading to inferior properties of the material The excess PbO added is not retained homogeneously as PbO volatilization is a surface phenomenon The excess free PbO remaining in the bulk material leads to Tc (ferroelectric to paraelectric phase transition temperature) shift and lower dielectric constant Another major problem associated with formation of PMN ceramics is the prevention of PbO volatilization during calcinations and sintering which in turn results in non-stoichiometry and lower density The powders with lower reactivity lead to incomplete solid state reaction during calcinations and to PbO loss and lower density during sintering Shrout (T R. Shrout and J Fielding, Jr Proceedings of the 1990 IEEE Ultrasonic Symposium, 711, 1990) has studied that the use of finer raw materials help in improvement of perovskite phase content as well as density With PMN powder of 70 nm, size they could achieve 90% theoretical density with pyrochlore phase 10% The citrate gel route adopted by Hong (Y S Hong et al J Euro Ceram Soc 18, 613, 1998) produced PMN ceramics with 98% perovskite phase but at the cost of lower sintering density Yet another problem in synthesis of PMN-PT powders is the large width pf MPB (x = 0 32) achieved due to inhomogeneity and lower reactivity of the powders Heterogeneity in composition gives mixed phases and wide MPB (J Kelly et al, J Am Ceram Soc 80, 957, 1997) US patent 4,265,668 issued to Fujiwara et al, in 1981 describes a high dielectric constant type ceramic composition based on lead magnesium niobate-lead titanate solid solution prepared by the conventional mixed oxide method The drawback of this process is that the starting materials are required in high purity (3N-4N) and hence making the process more expensive As such the solid state reactions are very sluggish resulting in unreacted second phases and formation of other intermediate compounds of inferior properties The detrimental pyrochlore phase problem is not addressed and emphasis has not been given to increase the reactivity of the constituents Perovskite Phase stabilization by the addition of BaTiO3 was not attempted to increase the polarization of the material The dielectric properties have been discussed in detail while the piezoelectric and electrostrictive properties have not been dealt with The application cited is for a compact and laminar capacitor and not for sensors actuators hydrophones, transducers and electro-optical devices as discussed in the present invention The calcinations (presmtenng) have been carried out at moderate temperature of 700-800 °C wherein the solid state reactions are sluggish and incomplete The basic ceramic composition has been modified by extravagant binary systems like Pb(Mn2/3 W1/3 )O3 Pb(Mn1/3Nb2/3 )O3, Pb(Mn1/2 Ta2/3 )O3, Pb(Mn1/2 W1/2)O3 and also with dopants like MnO and MgO Substitution in the Pb2" sites by Ba, Sr and Ca has been carried out to improve the dielectric constant of the basic ceramic formulation The properties at room temperature and at 1 kHz frequency have not been highlighted As discussed above, a number of fabrication processes have been reported to eliminate or minimize the pyrochlore phase, but most of these methods leave 3 -5% pyrochlore phase in the sintered product It has been recognized and well accepted that irrespective of the method used for PMN-PT preparation, there are other factors such as loss of PbO, reactivity of MgO, excess MgO, sintering temperature and time, mixing time etc, which controls the concentration of the pyrochlore phase in PMN- PT solid solution Among all the methods reported so far, Columbite has proved to be one of the most successful methods since it gives nearly single phase PMN-PT However, inhomogeneous mixing and sluggish reaction among the constituents in Columbite precursor leads to the formation of pyrochlore phase and subsequent deterioration of dielectric properties Hence new and alternate methods for reproducible single phase synthesis of PMN-PT are still being pursued Partial oxalate method, which eliminates difficulties in mixing the powders, has been successfully used for the preparation of many perovskite oxides including PZT (Pb (Zr1-x T1x) 03, PLZT (Lead Lanthanum Zirconium Titanate) and PMN (K Okazaki, Am Ceram Soc Bull, 67, 1946) However, this method has not been attempted for the preparation of PMN-PT solid solution ceramics It can be seen from the foregoing that it is virtually impossible to prepare PMN-PT with perovskite phase totally devoid of unwanted pyrochlore phase Use of excess MgO or PbO leads to the deterioration of much wanted dielectric and electromechanical properties Further, very little attempt has been made to eliminate the pyrochlore phase in the sintered product by optimizing the compaction and sintering parameters In view of the limitations and drawbacks of the existing art there is a need for process of preparation of PMN-PT ceramics giving reactive, stoichiometric, fine homogenous powders free from pyrochlore phase, sinterable to theoretical density with PbO loss, maintaining stoichiometry and having sharp MPB exhibiting superior physical, dielectric, piezoelectric and electrostnctive properties The present invention deals with these problems The process described herein gives highly reactive powders and noted simenng technique adopted ensures the prevention of PbO loss and achievement of high sintered density Due care has been taken in present invention for suppressing PbO volatilization providing PbO atmosphere by using loose powder or same composition Elimination of pyrochlore phase in the sintered product is ensured by optimizing the sintering parameters Pyrochlore phase free PMN-PT can be synthesized without addition of excess PbO and MgO during calcinations and sintering resulting in better homogeneity and stoichiometry The objective of this invention is to develop a process for the synthesis of pyrochlore phase free PMN-PT ceramics having exceptionally high dielectric and piezoelectric properties giving more emphasis on powder preparation and enhancing the reactivity of the constituents to achieve chemical homogeneity and stoichiometry in the sintered ceramics The use of magnesium carbonate (MgC03) instead of magnesium oxide (MgO) has beneficial effects by increasing the reactivity of MgO with Nb205 thereby forming the fully Columbite phase without leaving any unreacted Nb205 since nascent MgO with high reactivity is formed from the decomposition of MgC03 The addition of PbO as Pb(N03)2 solution assists in enhanced reactivity of the lead oxalate precipitate with the MNT mixture providing close contacts with the particles By this process the perovskite formation temperature is also lowered to 700-750°C wherein by the conventional mixed oxide route it is around 800-900°C The lead oxide has high vapour pressure around 800-900°C thereby creating Pb2+ vacancies and hence poor density and inferior dielectric and piezoelectric properties This problem is circumvented by using the carbonates and mixing the lead nitrate in the solution form Mixing of T1O2 with columbite phase results in further elimination of little amount of unreacted Mg4Nb2O9 phase which is responsible for formation of pyrochlore phase OBJECTS OF THE PRESENT INVENTION The primary objective of the present invention is to propose a novel semi-wet process for the preparation of ferroelectnc lead magnesium mobate-lead titanate (PMN-PT) ceramics free from pyrochlore phase, for capacitors, sensors, actuators and smart transducers for a wide range of applications in electronics, underwater detection and smart devices Another objective of the present invention is to propose a process which provides high surface area and reactive and sinterable powders of different compositions of PMN-PT ceramics leading to completion of desired solid state reaction and hence achieving minimum 99% of the theoretical density Another objective of the present invention is to propose a process to decomposition of as prepared powders to chemically homogenous mixture of their oxides Still another object of the present invention is to propose a process for the preparation of PMN-PT ceramics, which is energy efficient as the calcinations temperature of the present invention is around 1050 - 1100°C as compared to over 1150 - 1200°C respectively in the conventional solid- state process Yet another object of the present invention is to provide a process for preparation of PMN-PT ceramics which provides PMN-PT powder of sub-micron size of 0 50-1 00 microns which results in high reactivity for making bulk ceramics and leads to better quality products for sensors, actuators and smart device applications, Yet another object of the present invention is to provide a process for preparation of PMN-PT ceramics with controlled microstructure with average grain size of 5-7 microns which leads to better reproducibility Yet another object of the present invention is to provide a process for preparation of PMN-PT ceramics wherein the composition width of the morphotrophic phase boundary (MPB) coexistence region for tetragonal and rhombohedral phases is around 1% as compared to 15 to 32% in the conventional solid state process Still another object of the present invention is to propose a process for preparation of pure PMN and PMN-PT ceramics having high dielectric constant at room temperature and strong electrostnctive behaviour to obtain large(>l%) field induced strain Statement of Invention Accordingly the present invention provides a process for preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramics having formula (1-x) [Pb(Mg1/3 Nb2/3 )O3] x PbTiO3 comprising the steps of a) preparing Columbite phase (MN) powders (0 mixing and attrition milling of a mixture of 5 44-5 77 wt% of MgCO3 and 17 19-18 26 wt% of Nb2O5 for about 18- 24 hours in methanol media and Z1O2 grinding media, (II) drying the resultant mixture at 50-60° C for 3-6 hours, (III) calcining the mixture at 1050-1100° C for 4-6 hours, (IV) sieving the calcined powder through a 100-150 um mesh to remove large agglomerates, (v) repeating the attrition milling and calcination of MgCO3 and Nb2O5 powders till the formation of a single phase columbite without any unreacted MgO or Nb2O5 b) preparing MNT powders (vi) adding 2 21-2 22 wt% of BaTiO3 to the columbite precursor followed by addition of 8 10-9 14 wt% of TiO2, (vii) mixing and attrition milling the mixture thoroughly for 18-24 hours in methanol media, (viii) drying the resultant mixture at 50-60° C for 3-6 hours, (IX) calcining the resultant mixture at 1050-1100° C for 4-6 hours, (x) repeating the attrition milling and calcination to ensure a good bonding between the columbite precursor and the T1O2 powder, c) preparing PMN-PT powder (xi) sieving the calcined MNT powder through a 100-150 µm mesh to remove large agglomerates, (xii) dispersing slowly in 1 5M - 2M oxalic acid solution with continues stirring, (xiii) dissolving 101 88 -102 15 wt% Pb(N03)2 in water and heating at 200-300° C using a hot plate to prepare a homogeneous solution, (xiv) adding drop wise the solution as obtained in step (xiii) to the MNT mixture, (xv) filtenng the resultant nitric acid solution followed by washing the precipitate thoroughly with double distilled water and methanol to remove unwanted nitrates and impurities, (xvi) drying the precipitate at 50-60° C for 6-8 hours, (xvii) carrying out calcination of this precipitate in the tightly sealed alumina crucible assembly at a temperature of 750 ° C to avoid the lead oxide volatilization, (xviii) attrition milling the calcined powder at a speed of 250 rpm for 20-30 hours, (xix) drying the calcined powder at 60° and, (xx) carrying out calcinations of the powder in tightly sealed alumina crucible assembly at 750 ° C for 6 hours to yield pyrochlore free, homogeneous, fine PMN-PT powders d) fabricating PMN-PT ceramics (xxi) performing attrition milling of the calcined powder in the presence of methanol for 3-6 hours, (xxn) granulating the calcined powder to a uniform particle size, (xxni) adding 1-2 wt% PVA solution to the powder as binder compaction of the calcined powder was done using a steel die and hydraulic press at_an optimized pressure of 100-200 MPa, (xxiv) heating the resultant mixture at a rate of 0 5 - 1° C/minute to 500-700 C with a soaking time of 2 hours, (xxv) performing the sintering operation at a heating rate of 3° C/minute at 1150- 1280°C for a soaking period of 1-3 hours Electroding followed by poling by impregnating an external electric field /poling field of 2-4 KV/mm across the firmly fixed electroded sample, immersed in silicon oil bath at 60-120° C, for 30-60 minutes The present invention also provides a ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramic, substantially free from pyrochlore phase obtained by the above process, having molecular formula (1-x) [Pb (Mg 1/3 Nb2/3) O3] x Pb Ti O3 wherein x is more than 0 3 and less than 0 36 The present invention provides a novel semi-wet process (as compared to solid state process of the known art) for preparation of PMN-PT ceramics having molecular formula (1-x) [Pb(Mg1/3 Nb2/3 )O3] -x PbTiO3 with x varying from 0 to 0 40 preferably taking the value x=0, x=0 10 and x between 0 30 to 0 36 which are useful for electrostnctive and piezoelectric applications such as multilayer capacitors, electrostnctive strain actuators and underwater transducers The invention provides the complete process covering the preparation of PMN and PMN-PT powders as well as processing of these powders to sintered ceramics followed by electroding and poling and specific techniques developed for the measurement of electromechanical properties The process is time efficient, energy efficient and at the same time leads to ceramics, which are highly pure, stoichiometric, chemically homogenous and reproducible Chemical homogeneity is of critical importance in powders, as non-homogenous powders require relatively much higher temperature for calcinations, does not provide reproducibility in properties and leads to products with inferior properties The novelty in the invention lies both in preparations of PMN and PMN-PT powders and also in compaction and sintering of powders to form sintered ceramics The process of the present invention involves the preparation of MgNb2O6 phase from solid state reaction between MgCO3 and Nb205 by mixing them in stoichiometric proportion leaving no free MgO or Nb205 in the powder thereby completely suppressing the formation of undesirable pyrochlore phase in the powder The PMN and PMN-PT ceramics prepared by the known processes lacks reproducibility in essential characteristics desired for finished ceramics Further, the known process involves solid state mixing of oxides of Pb, Mg, Nb and Ti leading to inherent drawbacks of non-homogeneity and introduction of deleterious impurities in the powder The process of the present invention involves in the preparation of MgNb2O6 the first step by mixing and calcining pure MgCO3 and Nb205 in stoichiomeric proportion and ensuring no unreacted constituent in the calcined powder The calcined powder is then dispersed in 2M oxalic acid solution using specially designed magnetic-cum-stirrer whereby the solution of Pb(N03)2 was added drop by drop In this way, the calcined powder is homogenously dispersed with lead oxalate precipitate formed during the addition of Pb(N03)2 in oxalic acid The homogenous mixture is filtered and washed several times with distilled water and methanol till it is free from nitrate The filtered mass is dried in an oven and attrition milled and calcined at 750°C for 4-6 hrs in order to get stoichiometric PMN powder In another process, for the preparation of PMN-PT powder using the procedure mentioned above The procedure for processing the calcined powders of PMN and PMN-PT to sintered ceramics is same as described in succeeding paragraphs In the preparation of finished ceramics, the hydraulic pressure for the compaction of powders of required geometry such as pellets, cylinders etc and sintering variables like temperature, rate of heating and sintering time, have been optimized for desired characteristics in PMN and PMN-PT ceramics The compaction pressure of 100 to 200 MPa, sintering temperature in the range of 1000° C to 1200°C for 2 to 4 hrs, have been found to produce PMN and PMN-PT ceramics having unique combination of properties suitable for a wide range of applications as sensors and actuators in multilayer capacitors The process of the present invention enables calcinations and sintering at significantly lowers temperatures than the known processes and hence results in fine, homogeneous, single phase PMN-PT powders This invention will be fully understood from the following detailed description Detailed Description of the invention The present invention provides a process for preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramics having formula (1-x) [Pb(Mg1/3 Nb2/3 )O3]. x PbTiO3 comprising the steps of a) preparing Columbite phase (MN) powders (xxvi) mixing and attrition milling of a mixture of 5 44-5 77 wt% of MgCO3 and 17 19-18 26 wt% of Nb2O5 for about 18- 24 hours in methanol media and ZrO2 grinding media, (xxvii) drying the resultant mixture at 50-60° C for 3-6 hours, (xxviii)calcining the mixture at 1050-1100° C for 4-6 hours, (xxix) sieving the calcined powder through a 100-150 urn mesh to remove large agglomerates, (xxx) repeating the attntion milling and calcination of MgCO3 and Nb2O5 powders till the formation of a single phase columbite without any unreacted MgO or Nb2O5 b) preparing MNT powders (xxxi) adding 2 21-2 22 wt% of BaTiO3 to the columbite precursor followed by addition of 8 10-9 14 wt% of T1O2, (xxxii) mixing and attntion milling the mixture thoroughly for 18-24 hours in methanol media, (xxxiii)drying the resultant mixture at 50-60° C for 3-6 hours, (xxxiv) calcining the resultant mixture at 1050-1100° C for 4-6 hours, (xxxv) repeating the attntion milling and calcination to ensure a good bonding between the columbite precursor and the T1O2 powder, c) preparing PMN-PT powder (xxxvi)sieving the calcined MNT powder through a 100-150 urn mesh to remove large agglomerates, (xxxvii) dispersing slowly in 1 5M - 2M oxalic acid solution with continues stirring, (xxxviii) dissolving 101 88 -102 15 wt% Pb(N03)2 in water and heating at 200- 300° C using a hot plate to prepare a homogeneous solution, (xxxix)adding drop wise the solution as obtained in step (xiii) to the MNT mixture, (xl) filtering the resultant nitric acid solution followed by washing the precipitate thoroughly with double distilled water and methanol to remove unwanted nitrates and impurities, (xli) drying the precipitate at 50-60° C for 6-8 hours, (xlii) carrying out calcination of this precipitate in the tightly sealed alumina crucible assembly at a temperature of 750 ° C to avoid the lead oxide volatilization, (xliii) attrition milling the calcined powder at a speed of 250 rpm for 20-30 hours , (xliv) drying the calcined powder at 60° and, (xlv) carrying out calcinations of the powder in tightly sealed alumina crucible assembly at 750 ° C for 6 hours to yield pyrochlore free, homogeneous, fine PMN-PT powders d) fabricating PMN-PT ceramics (xlvi) performing attrition milling of the calcined powder in the presence of methanol for 3-6 hours, (xlvii) granulating the calcined powder to a uniform particle size, (xlvin) adding 1-2 wt% PVA solution to the powder as binder compaction of the calcined powder was done using a steel die and hydraulic press at_an optimized pressure of 100-200 MPa, (xlix) heating the resultant mixture at a rate of 0 5 - 1° C/minute to 500-700 ° C with a soaking time of 2 hours, (1) performing the sintering operation at a heating rate of 3° C/minute at 1150-1280°C for a soaking period of 1-3 hours Electroding followed by poling by impregnating an external electric field /poling field of 2-4 KV/mm across the firmly fixed electroded sample, immersed in silicon oil bath at 60-120° C, for 30-60 minutes One embodiment of the present invention provides the process as described above wherein the ceramics obtained are fully dense with grain size between 5-7 microns Another embodiment of the present invention provides the process as described above wherein the stirring speed in step (xn) is kept between 300-500 rpm Yet another embodiment of the present invention provides the process for preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramics as described above wherein the ceramics of electrostnctive composition are having high dielectric constant of 17500 and dielectric loss of 001 at room temperature Still another embodiment of the present invention provides the process for preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramics as described above wherein the ceramics of piezoelectric composition are having high dielectric constant of 5500, piezoelectric (d33) coefficient of 750 pC/N, field induced strain ( 0 1%), electromechanical coupling factor (0 62) and low dielectric loss of 0 015 Yet another embodiment of the present invention provides the process for preparation of ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramics as described above wherein the powder is free from pyrochlore phase with 99-100% pure perovskite phase PMN-PT powder Yet another embodiment of the present invention provides a ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramic, substantially free from pyrochlore phase obtained by the above process, having molecular formula (1-x) [Pb (Mg 1/3 Nb2/3) O3] -x Pb Ti O3 wherein x is more than 0 3 and less than 0 36 Still another embodiment of the present invention provides the ferroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramic wherein the morphotropic phase boundary is sharp (Ax= 0 01) and has coexistent tetragonal and rhombohedral phases The following experimental procedure provides an overview of the processing of (1-x-y) Pb (Mg1/3M)2/3 )O3 y BaTiO3 - xPbTiO3 for two select compositions x=0 10 and x=0 325 and y= 0 03 The basic constituents in the PMN-PT solid solution MgC03, Nb205, BaTi03, Ti02 and Pb (N03)2 were weighed as per the required stoichiometry The purity of the raw materials was >99 90% The process involves following steps 1 Preparation of Columbite phase (MN) powders Columbite precursor method was adopted to avoid the detrimental pyrochlore phase MgC03 and Nb205 were mixed and attrition milled thoroughly for about 18-24 hrs in methanol media and Zr02 grinding media The resultant mixture was dried at 50- 60 °C for 3 - 6 hrs and calcined at 1050 - 1100°C for 4 - 6 hrs The calcined powder was sieved through a 100 micron mesh to remove large agglomerates The whole process was repeated to ensure the formation of single phase columbite without leaving any unreacted MgO or Nb205 2 Preparation of MNT powders The phase stabilization of the perovskite phase was done after the columbite formation by adding BaTi03 followed by the addition of Ti02 which were mixed and attntion milled thoroughly for 18 - 24 hrs in methanol media The resultant mixture was dried at 50 -60°C and dried for 3 - 6 hrs and calcined at 1050 - 1100°C for 4-6 hrs The process was repeated again to ensure a good bonding between the columbite precursor and the Ti02 powders The resultant powder mixture may henceforth be named as MNT The formation of pyrochlore phase was suppressed by the addition of 3-5 mole% BaTi03 thereby stabilizing the perovskite phase The dielectric properties viz , dielectric constant, dielectric loss factor, and resistivity improved significantly with BaTi03 addition The addition of BaTi03 also lowered the ferroelectric to paraelectnc phase transition temperature (Curie temperature) 3 Preparation of PMN-PT powders This calcined MNT powder was sieved through a 100-150 microns mesh to remove large agglomerates and dispersed slowly in 1 5M-2M oxalic acid solution while the solution was constantly stirred Pb(N03)2 was dissolved in water and heated at 200 - 300 °C using a hot plate to prepare a homogenous solution This solution was taken in a burette and added dropwise to the MNT mixture The lead nitrate reacts with the oxalic acid solution to form lead oxalate, which gets uniformly coated on the MNT powders The resultant solution is the nitric acid, which is filtered out and the precipitate was dned at 50 - 60°C for 6-8 hrs The precipitate was washed thoroughly with double distilled water and methanol to get nd of unwanted nitrates and other impurities The partial oxalate setup has a rotostirrer with precise controller, which stirs the MNT mixture dispersed in the oxalic acid solution The magnetic stirrer speed is adjusted in such a way that the powder particles do not agglomerate and settle down The magnetic stirrer speed is kept between 300-500 rpm and preferably 400 rpm This is critical since if settling down of powder occurs then the coating process of the lead oxalate with the MNT particles will be significantly affected and hence the homogeneity of the resultant precipitate The uniformity of the coating process was analyzed through TGA and the weight loss when lead oxalate decomposes to lead oxide was recorded consistently and precisely The dispersion of the MNT powder, continuous stirring and the lead nitrate addition all were carried out in a systematic manner which makes the whole process an efficient one in forming fine, homogenous, single phase and fully perovskite PMN-PT powders 4 Fabrication of PMN-PT ceramics The calcined powder was first attrition milled in the presence of methanol for 3-6 hrs to break the agglomerated in the as calcined powder The calcined powder was granulated to a uniform particle size using a granulating machine This will assist in the homogeneous distribution of the particles and provide a close contact between them by reducing the level of porosity in the green body 1-2 wt% aqueous PVA solution preferably 2 wt% was added to this powder as binder Compaction of the calcined powder was done using a steel die of 12 mm diameter and uniaxial hydraulic press at an optimized pressure of 100 - 200 MPa Load optimization for the preparation of green pellets is an important step as it provides the maximum shrinkage of the material during sintering with densities close to the theoretical The binder was slowly burnt off by heating at a rate of 0 5-l°C/min to 600°C with a soaking time of 2 hrs Lead Oxide atmosphere was maintained inside the alumina crucible by keeping suitable amount of lead zirconate powder inside the assembly This PbO atmosphere of sufficient vapour pressure inhibits the volatilization of PbO from the pellets so that the weight of the pellet before and after sintering remains the same The sintering was carried out at a heating rate of 3 °C/min at temperature between 1150-1280°C for a soaking period of 1-3 hrs Fired on silver paste was used for electroding the sintered and flatly polished pellets The parallel surfaces of the pellets were cleaned by polishing with diamond paste (0 25 microns) and then washed with isopropanol After that silver paste was applied It was dried in oven at 150°C and subsequently fired at temperature between 500 - 700°C for 30-60 minutes The transformation of the ferroelectric ceramic to piezoelectric materials was done by impregnating an external electric field across the electroded sample by a process known as poling The parameters that affect the characteristic electomechanical behaviour of the material through this process are the poling field, time and temperature The samples were immersed in a silicone oil bath and firmly fixed using copper stubs The temperature of the oil bath was kept at 60-120 °C and poling field of 2-4 kV/mm was applied for a period of 30-60 minutes 5 Characterization of PMN-PT ceramics Liquid displacement method (Archimedes Principle) was used to determine the sintered density The density obtained varied from 98-99% of the theoretical X-ray diffraction analysis of both calcined and the sintered powders were carried out and the absence of pyrochlore phase and other inactive second phases was confirmed The XRD pattern was completely indexed and the presence of 100% fully perovskite phase was confirmed SEM analysis was earned out in the sintered pellet by polishing and chemically etching the specimen The average grain size obtained by linear intercept technique was 6-7 microns The particle size analysis was done by laser interferometry The average particle size obtained was 0 50 - 1 00 microns Examples Example 1 Preparation of 10 g of piezoelectric PMN-PT powder of composition (0 645) Pb (Mgi/3 Nb2/3 )03. 03 BaTi03 - (0 325)PbTi03 This working example can be followed to prepare a batch of lOOg or piezoelectric PMN-PT powder of composition (1-x-y) Pb (Mgi/3 Nb2/3 )03. y BaTi03 - xPbTi03 where x = 0 325 and y = 0 03 2 75 g of MgO (5 29 g of MgC03) and 18 14 g of Nb205 were weighed analytically, mixed and attrition milled at 120 rpm thoroughly in methanol media for 24 hrs The ratio of the powder to the zirconia grinding media was maintained 1 2 for attrition milling The mixture was dried at 60 ° C for 6 hrs The dried mixture was taken in an alumina crucible with a lid for tight sealing and calcined at 1100 C for 6 hrs The calcined powder was sieved through a 100 microns mesh to remove large agglomerates The attrition milling, calcination and sieving were performed again in an identical manner by maintaining similar conditions to ensure the formation of single phase Columbite without any unreacted MgO or Nb2O5 2 22 g of BaTiO3 was added to the Columbite precursor for the perovskite phase stabilization and attrition milled for 6 hrs 8 32 g of T1O2 was added thereafter and attrition milled for further 18 hrs period The mixture was dried at 60 °C and calcined at 1100 °C for 6 hrs The calcined powder was sieved through a 100 microns sieve to remove large agglomerates The attrition milling and calcination were repeated by maintaining the process parameters in an identical manner to complete the reaction between the constituents 68 57 g of PbO [210 40 g of Pb (NO3)2] solution was taken in a burette The MNT mixture was dispersed in a 2M oxalic acid solution while continuously stirring the solution The lead nitrate solution was added dropwise to react with the oxalic acid solution to form lead oxalate, which gets uniformly coated onto MNT powders The resultant nitric acid solution was vacuum filtered and the precipitate was thoroughly washed with distilled water and methanol to get rid of the nitrates and other impurities The precipitate was dried at 60 °C for 6 hrs The calcination of this precipitates was carried out in a tightly sealed alumina crucible assembly at a temperature of 750 °C for 6 hrs to avoid the lead oxide volatilization The calcined powder was attrition milled at a speed of 250 rpm for about 24 hrs and then dried at 60 °C and calcined in tightly sealed alumina crucible assembly at 750 °C for 6 hrs This process yields pyrochlore free, fully perovskite phase, homogenous, fine PMN-PT powders Example 2 Preparation of 100 g of electrostnctive PMN-PT powder of composition (0 87)Pb (Mgi/3Nb2/3) 03 - 0 03 BaTi03- 0 1 PbTi03 This working example can be followed to prepare a batch of 100 g of electrostnctive PMN-PT powder of composition (1-x-y) Pb (Mg1/3 Nb2/3 )O3. y BaTi03 - xPbTi03 whrere x = 0 1 and y = 0 03 3 65 g of MgO (7 02 g of MgC03) and 24 07 g of Nb205 were weighed analytically mixed and attrition milled at 120 rpm thoroughly in methanol media for 24 hrs The ratio of the powder to the zirconia grinding media was maintained 1 2 for attrition milling The mixture wad dried at 60 °C for 6 hrs The dried mixture was taken in an Aluminia crucible with a lid for tight sealing and calcined at 1100 °C for 6 hrs The calcined powder was sieved through a 100 microns mesh to remove large agglomerates The attrition milling calcinations and sieving were performed again in an identical manner by maintaining similar conditions to ensure the formation of single phase Columbite without any unreacted MgO or Nb2O5 2 19 g of BaTi03 was added to the Columbite precursor for the perovskite phase stabilization and attrition milled for 6 hrs 2 52 g of T1O2 was added thereafter and attrition milled for another 18 hrs The mixture was dried at 60 °C and calcined at 1100 °C for 6 hrs The calcined powder was sieved through a 100 microns sieve to remove large agglomerates The attrition milling and calcinations were repeated by maintaining the process parameters in the identical manner to complete the reaction between the constituents 67 57 g of PbO [207 30 g of Pb (NO3)2 ] solution was taken in a burette The MNT mixture was dispersed in a 2M oxalic acid solution while continuously stirring the solution The lead nitrate solution was added dropwise to react with the oxalic acid solution to form lead oxalate, which gets uniformly coated onto MNT powders The resultant nitric acid solution was vacuum filtered and the precipitate was thoroughly washed with distilled water and methanol to get rid of the nitrates and other impurities The precipitate was dried at 60 °C for 6 hrs The calcination of this precipitate was carried out in a tightly sealed alumina crucible assembly at a temperature of 750 °C for 6 hrs to avoid the lead oxide volatilization The calcined powder was attrition milled at a speed of 250 rpm for about 24 hrs and then dried at 60 °C and calcined in tightly sealed alumina crucible assembly at 750 °C for 6 hrs This process yields pyrochlore free, fully perovskite phase, homogenous, fine PMN-PT powders WE CLAIM: 1. A process for preparation offerroelectric Lead Magnesium Niobate-Lead Titanate (PMN-PT) ceramics having formula (1-x) [Pb(Mg1/3 Nb2/3)03] - x PbTi03 comprising the steps of: a) preparing Columbite phase (MN) powders: (li) mixing and attrition milling of a mixture of 5.44-5.77 wt% of MgCO3 and 17.19-18.26 wt% of Nb2O5 for about 18-24 hours in methanol media and ZrO2 grinding media; (lii) drying the resultant mixture at 50-60° C for 3-6 hours; (liii) calcining the mixture at 1050-1100° C for 4-6 hours; (liv) sieving the calcined powder through a 100-150 urn mesh to remove large agglomerates; (lv) repeating the attrition milling and calcination of MgCO3 and Nb2O5 powders till the formation of a single phase columbite without any unreacted MgO or Nb2O5; wherein "x" is more than 0.3 and less than 0.36. b) preparing MNT powders: (lvi) adding 2.21-2.22 wt% of BaTiO3 to the columbite precursor followed by addition of 8.10-9.14 wt% of TiO2; (lvii) mixing and attrition milling the mixture thoroughly for 18-24 hours in methanol media; (Iviii) drying the resultant mixture at 50-60° C for 3-6 hours; (lix) calcining the resultant mixture at 1050-1100° C for 4-6 hours; (lx) repeating the attrition milling and calcination to ensure a good bonding between the columbite precursor and the TiO2 powder; c) preparing PMN-PT powder: (lxi) sieving the calcined MNT powder through a 100-150 µm mesh to remove large agglomerates; (lxii) dispersing slowly in 1.5M - 2M oxalic acid solution with continues stirring; (lxiii) dissolving 101.88-102.15 wt% Pb(N03)2 in water and heating at 200- 300° C using a hot plate to prepare a homogeneous solution; (lxiv) adding drop wise the solution as obtained in step (xiii) to the MNT mixture; (lxv) filtering the resultant nitric acid solution followed by washing the precipitate thoroughly with double distilled water and methanol to remove unwanted nitrates and impurities; (lxvi) drying the precipitate at 50-60° C for 6-8 hours; (lxvii) carrying out calcination of this precipitate in the tightly sealed alumina crucible assembly at a temperature of 750°C to avoid the lead oxide volatilization; (Lxviii) attrition milling the calcined powder at a speed of250 rpm for 20-30 hours; (lxix) drying the calcined powder at 60° and; (lxx) carrying out calcinations of the powder in tightly sealed alumina crucible assembly at 750°C for 6 hours to yield pyrochlore free, homogeneous, fine PMN-PT powders, d) fabricating PMN-PT ceramics: (lxxi) performing attrition milling of the calcined powder in the presence of methanol for 3-6 hours; (lxxii) granulating the calcined powder to a uniform particle size; (lxxiii) adding 1-2 wt% PYA solution to the powder as binder compaction of the calcined powder was done using a steel die and hydraulic press at an optimized pressure of 100-200 MPa; (lxxiv) heating the resultant mixture at a rate of 0.5-1 °C/minute to 500-700°C with a soaking time of 2 hours; (1xxv) performing the sintering operation at a heating rate of 3°C/minute at 1150-1280°C for a soaking period of 1-3 hours.

Documents:

283-DEL-2005-Abstract-(23-01-2012).pdf

283-del-2005-abstract.pdf

283-DEL-2005-Claims-(06-06-2012).pdf

283-DEL-2005-Claims-(23-01-2012).pdf

283-del-2005-claims.pdf

283-DEL-2005-Correspondence Others-(06-06-2012).pdf

283-del-2005-Correspondence Others-(08-06-2012).pdf

283-DEL-2005-Correspondence Others-(23-01-2012).pdf

283-del-2005-correspondence-others.pdf

283-del-2005-description (complete).pdf

283-DEL-2005-Form-1-(23-01-2012).pdf

283-del-2005-form-1.pdf

283-del-2005-form-18.pdf

283-DEL-2005-Form-2-(23-01-2012).pdf

283-del-2005-form-2.pdf

283-del-2005-form-26.pdf

283-DEL-2005-Form-3-(23-01-2012).pdf

283-del-2005-form-3.pdf

283-DEL-2005-Form-5-(23-01-2012).pdf

283-del-2005-form-5.pdf

283-del-2005-GPA-(08-06-2012).pdf

283-DEL-2005-GPA-(23-01-2012).pdf