Title of Invention	"AN IMPROVED PROCESS FOR THE SYNTHESIS OF FERROELECTRIC RELAXOR MATERIAL"
Abstract	The present invention provides a method of low temperature single step perovskite phase synthesis of lead based ferroelectric relaxor materials using niobium tartarate complex and EDTA-complexes of constituent metals selected from Pb2+, Mg2+, Fe2+.

Full Text

This invention relates to an improved process for the synthesis of ferroelectric r&laxor material. Particularly it relates to a low temperature single step perovskite phase synthesis of lead based ferroelectric relaxor materials using niobium tartarate complex and EDTA-complexes of constituent metals. Relaxor ferroelectrics are used in the wide range electrochemical transducer application (Ferroeletrics 27 (1989) 31; J. Appl. Physics 51 (1981) 1142; Am. Ceram. Bull. 65 (1986) 647; Ferroelectrics 76 (1987) 241). They have interesting property in the field of piezoelectric & pyroelectric detectors. Compared with piezoelectric ceramics such as lead zirconate-titanate (PZT) ceramics, relaxor ferroelectric materials offer relatively high electric field induced stain (~0.1%) with a minima hysterisis effect. Moreover, since no polling process is involved, electrostrietive relaxor materials do not suffer strain again or creep, as found in most piezoelectric materials, limiting their use in certain applications. Moreover, ferroelectric relaxor materials in an attractive replacements for barium titanate in multilayer capacitors (MLCCs) because it can be sintered below 1000°C and thus low cost Ag or Cu can be used instead of noble metal internal electrodes such as platinum & palladium. A reference can be made to an article given bellow: J. Am. Ceram. Soc. 79 (1) 257-60 (1960) The common method for the preparation of relaxor mateials are through double calculation heterogeneous process (Equation Removed) where quality control is very difficult. Nb2O5 is the only available compound which is only used in solid state reaction. Fusion of the oxide (Nb2O5) with alkali metal carbonate followed by leaching of the cold melt with water leads to so called niobates. It is pointed out that sodium niobates are not very soluble, consequently the usual conventional addition of sodium carbonate to reduce the fusion temperature should be omitted. The main objective of the present invention is to provide 'a Low temperature single step perovskite phase synthesis of lead based ferroelectric relaxor materials using niobium tartarate and EDTA ( Ethylene diamine tetra acitic acid) - complexes of the constituent metals (Pb2+i Mg2+i Fe2+) which obviates the draw backs as detailed above. Still another objective of the present invention is water soluble niobium tartarate preparation which can be commercialized and it can be used for synthesis of single metal containing niobates and multiple metal containing niobates, eg. Lithium niobate which is a material in markets, complementary or competitive with Quartz. Another objective of the present invention is to synthesize niobates from the homogeneous reaction medium. Accordingly, the present invention provides an improved process for the synthesis of ferroelectric relaxor material characterized in that (a) preparing niobium tartarate by dissolving niobium oxide in HF ( hydrogen fluoride) , adding NH4OH to niobium fluoride solution to get niobium hydroxide followed by dissolving niobium hydroxide in tartaric acid to get niobium tartarate, (b) mixing thoroughly stoichiometric amount of niobium tartarate obtained in step (a) with metal-EDTA (ethylene diamine tetra acetic acid) complexes of the constituent metals selected from Mg, Pb, Fe or their mixture, evaporating the reaction product rapidly at 200°C to produce precursor powder, pyrolysing the obtained powder by heating at 500° -850°C for 2 to 4 hrs to get desired ferroelectric relaxor materials. In an embodiments of the present invention single step perovskite phase synthesis. In another embodiment of the present invention water soluble niobium tartarate is used. In Yet another embodiment of the present invention homogeniety of the reactants throughout the reaction. The process of the present inventions follwed the following steps: Step -1 Preparation of Nb-tartarate Nb2O5 dissolved in excess HF to produce a soluble [NbF7]2(~), ammonium oxalate (4M with respect to Nb2O5) was added to the fluoride solution. The solution was cooled and diluted and hen NH4OH was added to produce biobium hydroxide/hydrous niobium oxide (Nb2O5, nH20). Niobium hydroxide precipitate was filtered and was washed with distilled water. The precipitate was dissolved in tartaric acid (metal : tartaric acid = 1:2M) after heating on waterbath for 24 to 30 hrs. Now on evaporation solid niobium tartarate was obtained. Step - II The corresponding metal nitrates (Fe(N03)3, Zr(N03)2, Mg(NO3)2 etc.) was dissolved in Ammonical EDTA solution with Metal : EDTA ratio 1:1 to prepare soluble metal EDTA complex. The soluble metal complexes were then mixed with niobium tartarate solution. The mixture was rapidly evaporated on hot plate (~200°C) to produce precursor powder. Pyrolysis of this precursor produced the perovskite phase pure relaxor materials. Explanation Step -1 We have used Ammonium oxalate in the fluoride complex solution because on progressive neutralization of strongly acidic (HF) solution of Nb, a gradual polymerization occurs, up to colloidal dimensins and finally the hydrated oxides are precipitated. These polynuclear species are difficult to solubilize. Our approach is to reduce this polymeric chain by applying some complexing agents like ammonium oxalate. Similar results obtained if we use triethanol amine instead of ammonium oxalate. Pb(EDTA) & Mg(EDTA) complex is highly stable which prevent the precipitation of PbNb206 and thus making reaction medium homogenous throughout the reaction. The following example given by way of illustration of the present invention and should not be constried to limit the scope of the present invention. Example 1. Preparation Lead Magnessium niobate Pb(Mg1/3Nb2a)O2. Termed as PMN Mg(NO3)2 & Pb(NO3)2 with stoichiometric amount was solubilize in water and then mixed. Now EDTA was solubilise in dil amonia and pH was adjusted to 10 the metal nitrate mixture was added to the Edta solution with a mole ratio of metal : Edta (1:1). The soluble EDTA metal complex was then mixed with stoichiometric amont of Nb - tartarate solution (known from Nb2O5) and then rapidly evaporated on hot plate. After complete evaporation a fluppy mass was obtained which is known as precursor powder which on pyrolysis to 850°C/2h produced the perovskite phase pure PMN. Example 2. Preparation Lead Iron niobate Pb(Fe1!2Nbie)O3. Termed as PFN Fe(NO3)3 & Pb(NO3)2 with stoichiometric amount was solubilize in water and then mixed. Now EDTA was solubilise in dil amonia and pH was adjusted to 10 the metal nitrate mixture was added to the Edta solution with a mole ratio of metal : Edta (1:1). The soluble EDTA metal complex was then mixed with stoichiometric amont of Nb - tartarate solution (known from Nb2O5) and then rapidly evaporated on hot plate. After complete evaporation a fluppy mass was obtained which is known as precursor powder which on pyrolysis to 800°C/2h produced the perovskite phase pure PFN. The main advantage of the present invention are 1. Soluble niobium tartarate preparation 2. One calcination step used (850°C) 3. Single step perovskite phase obtained 4. It is also being sintered at low temperature (1000°C) 5. It can be replaced BaTiO3 in Multi Layered Capacitors (MLCCs). We Claim: 1. An improved process for the synthesis of ferroelectric relaxor material characterized in that (a) preparing niobium tartarate by dissolving niobium oxide in HF ( hydrogen fluoride) , adding NH4OH to niobium fluoride solution to get niobium hydroxide followed by dissolving niobium hydroxide in tartaric acid to get niobium tartarate, (b) mixing thoroughly stoichiometric amount of niobium tartarate obtained in step (a) with metal-EDTA (ethylene diamine tetra acetic acid) complexes of the constituent metals selected from Mg, Pb, Fe or their mixture, evaporating the reaction product rapidly at 200°C to produce precursor powder, pyrolysing the obtained powder by heating at 500° - 850°C for 2 to 4 hrs to get desired ferroelectric relaxor materials. 2. An improved process for the synthesis of ferroelectric relaxor material substantially as here in described with reference to the examples.

Documents:

159-del-2000-abstract.pdf

159-del-2000-claims.pdf

159-del-2000-correspondence-others.pdf

159-del-2000-correspondence-po.pdf

159-del-2000-description (complete).pdf

159-del-2000-form-1.pdf

159-del-2000-form-19.pdf

159-del-2000-form-2.pdf

159-del-2000-form-3.pdf