Title of Invention	A METHOD FOR THE PROSUCTIONOF SEMI CONDUCTOR-GRADE PEROVSKITE TITANATE COMPOUNDS AND THEIR SOLID SOLUTIONS
Abstract	57) Abstract: This invention relates to a method foir the production of perovst\kite titanate compounds of formula ABO, where 'A' is divalcent and 'B' is tetravalent cationb and their solid solutions Comprising: Purifying the starting material of general gormula X,Y, (where X denotes metal ions Ti,Zr,Ba, Sr, Ca and Pb and 'Y' denotes cholrides or nitrates and a 1 and b-2-4, if Y denotes nitrate, X is Pb) by in sity fractional precipitation involving preferential segregation of impurities into the solid, leading to a pre- determined impurity contents, co-precipitating the crystalline hydrated carbonates ofr Ba, Pb, Ca or Sc along with the hydrated titania, Zirconia or Strannia by the addition of ammonium Carbonate at 30-40 degree C to the corresponding chlorides or nitrate solution till the pH is 8, Washing the precipitate with water to make it free of the anions (C1 or No3) and ammonium inons. drying the said precepitate at 100-120 degree C followed by calcination at below 800°C PRICE: THIRTY RUPEES

Title of Invention

A METHOD FOR THE PROSUCTIONOF SEMI CONDUCTOR-GRADE PEROVSKITE TITANATE COMPOUNDS AND THEIR SOLID SOLUTIONS

Abstract

57) Abstract: This invention relates to a method foir the production of perovst\kite titanate compounds of formula ABO, where 'A' is divalcent and 'B' is tetravalent cationb and their solid solutions Comprising: Purifying the starting material of general gormula X,Y, (where X denotes metal ions Ti,Zr,Ba, Sr, Ca and Pb and 'Y' denotes cholrides or nitrates and a 1 and b-2-4, if Y denotes nitrate, X is Pb) by in sity fractional precipitation involving preferential segregation of impurities into the solid, leading to a pre- determined impurity contents, co-precipitating the crystalline hydrated carbonates ofr Ba, Pb, Ca or Sc along with the hydrated titania, Zirconia or Strannia by the addition of ammonium Carbonate at 30-40 degree C to the corresponding chlorides or nitrate solution till the pH is 8, Washing the precipitate with water to make it free of the anions (C1 or No3) and ammonium inons. drying the said precepitate at 100-120 degree C followed by calcination at below 800°C PRICE: THIRTY RUPEES

Full Text	This invention relates to a method for the production of F'erovskite titanate compounds of general formula ABO, where A' is divalent and B^ is tetravalent cation and their solid solutions. The said compounds are BaTiQ, SrTiO CafiO^ and PbTiO^and their solid solutions - (Ba, Pb)riO^.(Ba, Sr)Tiq. Ba(Sn;ri) BACKGROUND The perovskite titanate compounds of general formula ABO, such as Ba'fiQ SrTiO PbTiO PbZrO and their solid solutions are archet>'pal electronic ceramics with a long history of technological applications in the electronic industry (1). Increasing demands on the quality of electronic ceramics have led to greater sophistication in the processing of these materials both at the powder synthesis stage and subsequent densification to solid components or thin dielectric layers. The growing awareness of the need for scientific elegance in processing electroceramic powders before firing is clear in much of the current emphasis on novel low-temperature synthesis techniques. Various wet chemical routes have been described in literature for the preparation of the perovskites (2). Each one of these processes has its own limitations (as listed in Table 1) as far as commercialisation is concerned. ine object of this invention is to develop a process, which would obviate the aforesaid limitations and is more economical. To achieve the said objective this invention provides a method for the production of perovskite titanate compounds of formula ABO3 where 'A' is divalent and 'B' is tetravalent cation and their solid solutions comprising: purifying the starting material of general formula XaYb (where X denotes metal ions Ti, Zr, Ba, Sr, Ca and Pb and 'Y' denotes chlorides or nitrates and a=l and b=2-4, if Y denotes nitrate, X is Pb), by in situ fractional precipitation involving prefCTcntial segregation of impurities into the solid, leading to a pre-determined impurity contents, co-precipitating the crystalline hydrated carbonates of Ba, Pb, Ca or Sr along with the hydrated titania, Zirconia or Stannia by the addition of ammonium carbonate at 30-40 degree C to the corresponding chlorides or nitrate solution till the pH is 8, washing the precipitate with water to make it free of the anions (CI or NO3) and ammonium ions, drying the said precipitate at 100-120 degree C followed by calcination at below 800°C. The starting materials of general formula are TiCl2, ZrOCli, BaCL2, SrCl2, CaCli, Pb(N03)2 and the washing of the precipitate is carried out with deionised water. The starting material TiCl^ and ZrOCl^ are puritlcd b\ dissoh.ing the said materials separately in deionised water and therealler adding ammonia to precipitate titania gel and zirconia gel, the fractionallv tbnncd precipitate cam.' the impurities of transition metal ions - Fe, Mn, Cr, Co and Ni. Ihe ammonia used is concentrated ammonia solution. The BaCl^is purified by dissolving it in deionised water and IICl is added till the HaCI J. is precipitated by common ion effect leaving all the impurities in the strongly acidic solution and the precipitate is washed free of HCI using ethyl alcohol and dried at 120 degree C. The HCI used is concentrated HCI. The Pb(NOj) is purified by dissolving it in deionised water and HNO^ is added till Pb(N03) is precipitated by common ion efTect and the precipitate then is washed with distilled ethyl alcohol till it is free of IINO^ and dried at 120 degree C. The HNQ- used is concentrated HNO,. The pre-determined impurity contents are around 10 parts per million and the calcination is carried out below 800 degree C. rhe precipitate, if necessary, is homogenized by blending the precipitate in deionised water or ethyl alcohol medium with constant stirring for about an hour. This step is optional. Blending is necessary, particularly when the concentration of solutions are high, stirring is improper or when there is improper order of addition while mixing the solutions. During the co-precipitation step the carbonates of titanium or zirconium are not formed, as they are unstable. Moreover, the titanium or the zirconium ion has a tendency to form polymeric chams such as Ti-O-Ti or Zr-O-Zr m preference to Ti -It orZr ions. The latter is least stable due to high ratio of charge to ionic radius. In addition, the Ti which prefers octahedral coordination cannot be stabilised by the carbonate ligands due to steric reasons. Therefore the hydrated titania gel is stabilised, wherein partial substitution of the terminal hydroxyls by carbonate group is possible. The rate of addition of ammonium carbonate which is an important factor, has to be faster so that fine particles of carbonates are precipitated, which remain embedded within the hydrated titania gel. The invention will now be described by way of an illustration for the production of Ba'fiO and its solid solutions (Ba,Sr)TiO , (Ba,Pb) fiO , Ba(Sn,Ti)0,, Ba(Zr,Ti)0 and PbTiQ and its solid solutions (PZT), as determined by x-ray diffraction patterns, as shown in the accompanying drawings. Brief description of tiic drawings l-ig. I x-ray dillraccion paitcrnol I'bl'iO, calcined at diMcrcut temperatures. I'ig. 2 TG/DTA of as-prepared powder of F'bTiO,. l-ig. 3 X-ray dilfractioii pattern^ot Pb(Zr„5, ri„5)0., calcined at dillerem temperatures. i'ig. 4 X-ray dilTractogram of BaTiO, heat treated at differcni temperatures. Pig. 5 X-ray dilTractogram of (Ba„75,Sr„j,)Ti03 solid solution calcined at different temperatures. I'ig. 6 Resistivity {p) - Temperature (I) characteristics of (a) n-BaTiO,, (b) n-(Ba«,7j,Sr„2j)Ti03 and (c) n-(Ba 1000 ml of 'riCl4 (~ 98 % purity) is diluted to 4000 ml in deionised water under ice-cold coiidilioiis lo form titanium oxycliloride (1 iOCIj) solution. I'o this clear solution, about 60-70 ml of concentrated ammonia solution is added to partially precipitate the litania gel. The fractionally formed precipitate carry the itnpurities along with ii. spccilically the leiric ions. I lii gel \s separated by lilteration and discarded. Tlie process is repealed once again il ihc iniiial iron contem is high (>l %)• Ihc TiO, content in the impurity-tree TilKl, solution is tlicn 0 estimated. When a solid Is separating out Irom a homogeneous solution as a precipitate, the impurity distributes between the solid formed and the original solution. It the impurities have chemical coherence with one or more elements present in the precipitate, the impurities will be solely present in it, rather than in the solution. In the case of litanates and zirconates, the Impurities are mostly transition tiietal ions (F"e. Mn, Cr. Co and Ni) which have complete cohercticc with the titanium or zirconium so that even the incipiently lornied piecipitate tarries most of Ihc Impurities. The present invention makes use of this principle. (b) Barium Chloride (IJaClj .211,0) 500 g of liaCI, .211,0 ( ~ 98 % purity, l.aboialory Rcageni tirade) is dissolved in 1.5 litres of dcionised water. To this solution, 500 ml of conceniralcd hydrochloric acid (35 wt %) is added till all the barium chloride is precipitated, leaving all the impurities in the Strongly acidic solution. Precipitation occurs because of the coimiion ion effect. I he precipitate is washed free of hydrogen chloride using ethyl alcohol and dried at I20"C. (c) Uad Nitrate IPblNOj)^] 500 g of lead nitrate ( ~ 98 % purity, Uiboralory Reagent Grade) is dissolved in about 2 litres of deionised water. To this solution, 500 ml of concentrated nitric acid is added so that lead nitrate precipitates by common ion effect. The impurities are left behind in the strongly acidic solution. The precipitate is then washed with disiilled,cthyl alcohol, till it is free of nilric acid and dried at 120"C for 6 h. (di Zirconium Oxychloride (ZrOClj) 500 g of ZrOCI, is dissolveci in about 2 litres ol cicioniscci water. I o this is added ammonia lo Iraciionally precipiiat'e zirconia gel wliich carries away all the impurities. The gel is then filtered and discarded. The impurity tree ZrOCI, solution is the.i made use of for the preparation of perovskiie solid solutions. Example 1 Lead TItanate (PbTiOj) To 1330 ml of pure TiOCI, solution containing 262 gins of TiO,, about 1000 ml of concentrated ammonia solution is added to precipitate the titania gel at 30-40"C (pli is maimaitied at - 8). The gel is washed free of the chloride ions and ammonium ions. The chloride free gel is (hen dissolved In 1000 ml of concentrated nitric acid diluted to 4(KK) ml. Hie mixture has to be preserved for 4 h to obtain clear solution. To the clear solution of (itanyl nitrate, 1100 gms of lead nitrate (purified) is added and fractionally coprecipitated by the addition of 130 ml of amtjionium carbonate. The \|)rccipitalc is then removed by liltraiion and discarded. 6400 ml of ammonium carbonate { ~ 2M coiicciitralioii) is then added to the purified solution at 30-40'C (pll is maintained at ~ 8). resulting in a precipitate containing lead carbonate particles embedded in hydrated titania gel. The precipitate is washed free ol the nitrate and ammoniuin iotts. It is then homogenised in deioni,sed water or ethyl alcohol medium. u The x-ray diffraction pattern of the powders calcined at different temperatures r are shown in l-ig. I. Ihe x-ray diffractogram of the as-prepared powder dried at I20"C for 10 h showed the presence of lead carbonate (PbCXJ,) as (he ciystalline phase. No titanium .dioxide (TiO ) is detected since it is in the amorphous form by way of hydrated titania. Heat treatment of the powder at - 275 degree C. for 4 h, results in the formation of PbO with tetragonal symmetry, whereas no rctlections of TiO^ (neither anatase nor rutile) are observed. On calcining at 350 degree C for 4 h, x-ray reflections of PbO (tetragonal) and Pb^TijD^ of defect pyrochlore structure are observed. When the duration of calcination at 350 degree C is extended to more than 12 h, the intensities of the reflection from Pb^^TiJI)^ has increased. The formation of the defect pyrochlore, Pb.Ti 0_ , where x=L is reported in literature from the borosilicate glass matrix containing"lead and titanium dioxide (16). This defect pyrochlore dphase has the same composition as that oJ" the pcrovskite. although it has a different crystal structure. As the calcination temperature is mcreased above 350 degree C, reflections of PbO (tetragonal) shifts to larger 20-values, indicative of the decreased d - spacings as well as the cell parameters. This arises from the partial dissolution of TiO in PbO (tetragonal) to form a solid I solution, designated as \|(l>b0.xTiO,),J. Thus at the calcination temperature ol 40()'X^ lor 4 h. x-ray rellections of PbTiO^ (perovskite), PbO.xTiO, (0 Thermoanalytica! results (IG/DTA) of the as picpatcd powder (lig. 2) shows (lie weight loss in three steps: (i) below lOOT (~ 6 %), due to the loss of free 11,0 retained in the solid, (ii) around 260"C (~ 4 %), corresponding to the decomposition of VhCO, and (iii) around 300-320T ( ~ 2.5 %), due to the reaction ol amorphous hydroxylated tiiania with PbO accompanied by the release of water due to dehydroxylation. I here is little weight loss above 350"C (~ 0.5 %). The corresponding endoiliernjs are observed around ()()"(', 255"(" and 3()()"C (Pig. 2) in the TG/DTA curves. The powders prepared are Irigl.ly reailive hccaiise ,>f .he low .emperalurc ol formation of the product. The product-yield is nbearly quantitave. 98 % Highly crystalline and phase pure powders are obtained. Example 2 Lead zirconium titaiiate (PZT) To a solution containing 1^50 ml of TiOCI^ (containing 246 gms of TiO,) and 993 gms of ZrOCIj. about 1000 ml of concentrated ammonia solution is added to precipitate the hydroxides of titaniutn and zirconium. The gel is washed tree of chloride and ammonium ions using deionised water. It is then dissolved in 1250 ml of concentrated nitric acid diluted to 3750 ml, by allowing to stand for 6 hours. To the clear solution of tiiaiiyl zirconyl nitrate. 2040 gms of lead nitrate is added and fractionally coprecipilated by the addition of 300 ntl ot ammonium carbonate of 2 M conceiuration. The prccipilalc is removed by lillralion. To ihc puritied solution, 6000 ml of annnonium carbonate ( ~ 2M) is added al 30 40"(' (pi I nuiiniaincd at ~ 8) to form the composite precipitate. The precipitate is washed free of nitrate and ammonium ions. It is then homogenised in deionised water or ethyl alcohol medium lor an hour, using a magnetic stirrer having teflon coated paddle and dried at I20"(^ for 10 h. I'iiis is followed by the calcination step at elevated temperatures, as in l-xatnple I. Fig. 3 shows the x-ray diffraction pattern of the powders calcined at different temperatures. The as-prepared powder (dried at I2()"(:) showed the presence of the crystalline lead carbonate phase. Heat treatment at 400"C for 4 h results in tfie formation of the mixed phases namely, perovskite \|Pb(Zru5,Tio5)03)\|(I'ZT), PbO and the defect pyrochlore phase \|(Pb,(Zr„5,Ti„5)jOJ. Further annealing at 45()"C for 24 h results in the evolution of a crystalline phase of the perovskite. 'Example 3 Barium titanate (BaliOj) The procedure described in Example 1 is followed. The starting reaction mixtures are; purified aqueous titanyl chloride and barium chloride. 1070 gms of this soluble salt of barium is dissolved in 1740 ml of titanium oxychloride solution (containing 343 gms of TiO,) and were fractionally coprecipitated by the addition of 170 ml of ammonium carbonate of 2 M concentration. The precipitate is removed by filtration. 8350 ml of ammonium carbonate (- 2M concentration) is then added to the purified solution at 30-40"C (with the pM maintained at ~ 8), to coprccipitatc the carbonate of barium alongwith the hydraied tiiania. The precipitate is (hen washed free of chloride and ammonium ions. It is then homogenised in deioniscd water or distilled ethyl alcohol medium for about an hour and then dried at I20"C' for about 10 h. This is lollowed by calciiialioii at elevated temperatures. The x-ray diffraction pattern of the as-prepared powder dried at I2()"C tor 10 h, showed the presence of BaCOj. No x-ray reflections of TiO, is observed, indicating that it is present as hydrated titania gel which is x-ray amorphous. Meat treatment at 450T for 4 h,showed the persistence of only the carbonate phase. Further annealing at 650"C' resuhed in the formation of mixed phases namely, the major phase was that of the perovskiie (Ma liO,) and the minor phase corresponding to the defect Ba-pyrochlore (Bajl i,OJ. At temperatures -800'C. )hase pure and highly crystalline phase of the perovskite, i.e. BaTiOj is obtained. The amount f powder obtained is around 1000 gms, corresponding to ~ 98 % yield. The impurity contents I the resulting powders were determined by atomic absorption, spectrometry and the total incentrations of Fe, Co, Ni, Mn and Cr were less than 20 ppm. Example 4 Solid solutions of BaTiO3 1840 ml of titanium oxychloride (containing - 362 gms of TiC2) is diluted to 2 litres in deionised water. To this, 830 gms of BaCI^ .2H^J and 302 gms of SrCl ^ .6H^0 were added and fractionally co-precipitated along with titania by the addition of 180 ml of ammonium carbonte (2M). The precipitate is removed by filtration and discarded, To this purified solution, about 8850 ml of ammonium carbonte (- 2M concentration) is added at 30-40 degree C (pH is maintained at -8) to form the composite precipitate. The precipitate is washed free of chloride and ammonium ions. It is then homogenised by constant stirring in deionised water or ethyl alcohol medium and dried at 120 degree C for 10 h. The resultant powder was flowing. The powder was then calcined at elevated temperatures ( 800 degree C) to give the resultant crystalline phase of (Ba , Sr )TiO. The mass of the product obtained is - 1000 gms. Fig. 5 shows the x-ray diffraction pattern of (Ba , Sr ,)TiO . The x-ray diffractogram of the as - prepared powder (dried at 120 degree C) shows the presence of BaCO^, SrCO^ phases along with the amorphous hydrated TiO . Heat treatment at 650 degree C for 6 h showed the persistence of the mixed phases, the major phase being that of the perovskite and the minor phase corresponding to the defect pyroclilorc. Further heat ireat.ncnt at ~ 800°C or 6 h leads to a crystalline phase pure solid solution. The cell parameter (a) calculated lo be 3.97 A agrees well with the reported values 117]. The method is extended lor the preparation ot (Ba,,. Srj IKJ (where x = 0 to 1) by varying the Ba/Sr ratios in the precipitation. Various other solid solutions of perovskites were prepared by the above procedure. They are listed below: (a) (Ba,.„PbjTiO, x = 0 to 0.6 (b) Ba(Sn„Ti,.,)0, x = 0 to 1.0 (c) Ba(Zr„Ti,.,)0, x = Oto 1.0 (d) (Ba,..+,,Sr.,Cay)TiO, x = 0 to 0.5, y = 0 to 0.3 Semiconducting ceramics based on BaI'iO, and its solid solutions prepared from powders derived from the prescni route are lound to give cxcclleni VVCR (positive temperature cocrticicm ol resistance) characteristics (l-jg. 6), po.s.sibly hccau.sc of the absence o( the alkali. This clearly shows that the products obtained through this route are phase pure. References , A.J. Moulson and J.M. Herbert,,Electroceraics, Chaoman & Hall, London, 1990 2. P.P. Phule and S.H. Rlsbud, J. Mater. Sci. 25 (1990) 1169. 3. P. Padmini and T.R.N. Kutty. J, Mater, Sci; Materials in l-lcctroiiics. 5 (1994) 203. 4. K.S. Mazdiyasiii et al. US Patent 3647364, March (1972). 5. K.S. Mazdiyasiii and L.M. Brown, J. Am. Ceram. Soc. 55 (1972) 633. 6. A.N. Christensen, Acta Chem. Scand. 24 (1970) 2447. 7. H. Okada, H. Maisubayaslii and I". Goto, Japanese Patent JP 6272525 A2\|87/72425\|. March (1987). 8. W.S. Claubaugh. E.M. Swiggard atid R. Gilchrist, J. Res. Nat. Bur. Std. 56 (1956) 289. 9. P.P. Phule and S.ll. Ri.sbud, Mater. Sci. lingg. H3 (I9«9) 241. 10. J.M. Wilson, D.L. Coller and S. Venkalaraniani. US Patent 4670243, June (1987). 11. M. Pechini. US Patent 3330697, July (1967). 12. B.J. Mulder, Ceram. Bull. 49 (1970) 990. 13. S. DiViia and R.J. Fischer, U.S Patent 2985506, May (1961). 14. A.S. Shaikh and G.M. Vest, J. Am. Ceram. Soc. 69 (1986) 682. 15. A. Beauger, J.C. Mutin and J.C. Niepece, J. Mater. Sci. 18 (1983) 304. 16. Martin, Phy. Chem. Glasses, 6 (1965) 143. 17. T.R.N. Kutty and P. Padmini, Mater. Res. Bull. 27 (1992) 945. We claim: 1. ' A method for the production of perovskite titanate compounds of formula ABO3 w^iere 'A' is divalent and 'B' is tetravalent cation and their solid solutions comprising: purifying the starting material of general formula XgYb (where X denotes metal ions Ti, Zr, Ba, Sr, Ca and Pb and 'Y' denotes chlorides or nitrates and a=l and b=2-4, if Y denotes nitrate, X is Pb), by in situ fiactional precipitation involving preferential segregation of impurities into the solid, leading to a pre¬determined impurity contents, co-precipitating the crystalline hydrated carbonates of Ba, Pb, Ca or Sr along with the hydrated titania, Zirconia or Stannia by the addition of ammonium carbonate at 30-40 degree C to the corresponding chlori(ks or nitrate solution till the pH is 8, washing the precipitate with water to make it free of the anions (CI or NO3) and ammonium ions, drying the said precipitate at 100-120 degree C followed by calcination at below 800°C. 2. A method as claimed in claim I wherein the starting materials of general formula are TiCl2, Z1OCI2, BaCLz, SrClz, CaCh, Pb(N03)2. 3. A method as claims in claim 1 wherein the starting material TiQi and ZrOCh are purified by dissolving the said materials separately in deionised water and thereafter adding ammonia to precipitate titania gel and zirconia gel, the fractionally formed precipitate carry the impurities of transition metal ions - Fe, Mn, Cr, Co and Ni. 4. A method as claimed in claim 3 wherein the ammonia used is concentrated ammonia solution. *5. A method as claimed in claim 1 wherein BaCb is purified by dissolving it in deionised water and HCl is added till the BaCb is precipitated by common ion effect leaving all the impurities in the strongly acidic solution and the precipitate is washed free of HCl using ethyl alcohol and dried at 120 degree C. 6. A method as claimed in claim 5 wherein HCl used in concentrated HCl. 7. A method as claimed in claim 1 wherein Pb(N03)2 is purified by dissolving it in deionised water and HNO3 is added till Pb(N03)2 is precipitated by common ion effect and the precipitate then is washed with distilled ethyl alcohol till it is free of HNO3 and dried at 120 degree C. 8. A method as claimed in claim 7 wherein HNO3 used is concentrated HNO3. 9. A method as claimed in claim 1 wherein said predetermined impurity contents are around 10 parts per million. 10. A method as claimed in claim 1 wherein solid solutions are (Ba,Sr)Ti03, (Ba,Pb)Ti03, Ba(Sn,Ti)03, Ba (Zr,Ti)O3 and PZT. 11. A method for the production of perovskite titanate compoimds of formula ABO3 where 'A' is divalent and 'B' is tetravalent cation and their solid solutions substantially as herein described with reference to the foregoing examples.

Full Text

This invention relates to a method for the production of F'erovskite titanate compounds of general formula ABO, where A' is divalent and B^ is tetravalent cation and their solid solutions. The said compounds are BaTiQ, SrTiO CafiO^ and PbTiO^and their solid solutions - (Ba, Pb)riO^.(Ba, Sr)Tiq. Ba(Sn;ri) BACKGROUND
The perovskite titanate compounds of general formula ABO, such as Ba'fiQ SrTiO PbTiO PbZrO and their solid solutions are archet>'pal electronic ceramics with a long history of technological applications in the electronic industry (1). Increasing demands on the quality of electronic ceramics have led to greater sophistication in the processing of these materials both at the powder synthesis stage and subsequent densification to solid components or thin dielectric layers. The growing awareness of the need for scientific elegance in processing electroceramic powders before firing is clear in much of the current emphasis on novel low-temperature synthesis techniques.
Various wet chemical routes have been described in literature for the preparation of the perovskites (2). Each one of these processes has its own limitations (as listed in Table 1) as far as commercialisation is concerned.

ine object of this invention is to develop a process, which would obviate the aforesaid limitations and is more economical.
To achieve the said objective this invention provides a method for the production of perovskite titanate compounds of formula ABO3 where 'A' is divalent and 'B' is tetravalent cation and their solid solutions comprising:
purifying the starting material of general formula XaYb (where X denotes metal ions Ti, Zr, Ba, Sr, Ca and Pb and 'Y' denotes chlorides or nitrates and a=l and b=2-4, if Y denotes nitrate, X is Pb), by in situ fractional precipitation involving prefCTcntial segregation of impurities into the solid, leading to a pre-determined impurity contents,
co-precipitating the crystalline hydrated carbonates of Ba, Pb, Ca or Sr along with the hydrated titania, Zirconia or Stannia by the addition of ammonium carbonate at 30-40 degree C to the corresponding chlorides or nitrate solution till the pH is 8,
washing the precipitate with water to make it free of the anions (CI or NO3) and ammonium ions,
drying the said precipitate at 100-120 degree C followed by calcination
at below 800°C.
The starting materials of general formula are TiCl2, ZrOCli, BaCL2, SrCl2, CaCli, *Pb(N03)2 and the washing of the precipitate is carried out with deionised water.

The starting material TiCl^ and ZrOCl^ are puritlcd b\ dissoh.ing the said materials separately in deionised water and therealler adding ammonia to precipitate titania gel and zirconia gel, the fractionallv tbnncd precipitate cam.' the impurities of transition metal ions - Fe, Mn, Cr, Co and Ni. Ihe ammonia used is concentrated ammonia solution.
The BaCl^is purified by dissolving it in deionised water and IICl is added till the HaCI J. is precipitated by common ion effect leaving all the impurities in the strongly acidic solution and the precipitate is washed free of HCI using ethyl alcohol and dried at 120 degree C. The HCI used is concentrated HCI.
The Pb(NOj) is purified by dissolving it in deionised water and HNO^ is added till Pb(N03) is precipitated by common ion efTect and the precipitate then is washed with distilled ethyl alcohol till it is free of IINO^ and dried at 120 degree C. The HNQ- used is concentrated HNO,.

The pre-determined impurity contents are around 10 parts per million and the calcination is carried out below 800 degree C.
rhe precipitate, if necessary, is homogenized by blending the precipitate in deionised water or ethyl alcohol medium with constant stirring for about an hour. This step is optional. Blending is necessary, particularly when the concentration of solutions are high, stirring is improper or when there is improper order of addition while mixing the solutions.
During the co-precipitation step the carbonates of titanium or zirconium are not
formed, as they are unstable. Moreover, the titanium or the zirconium ion has a
tendency to form polymeric chams such as Ti-O-Ti or Zr-O-Zr m preference to Ti
-It orZr ions. The latter is least stable due to high ratio of charge to ionic radius. In
addition, the Ti which prefers octahedral coordination cannot be stabilised by the
carbonate ligands due to steric reasons. Therefore the hydrated titania gel is
stabilised, wherein partial substitution of the terminal hydroxyls by carbonate
group is possible.
The rate of addition of ammonium carbonate which is an important factor, has to be faster so that fine particles of carbonates are precipitated, which remain embedded within the hydrated titania gel.
The invention will now be described by way of an illustration for the production of Ba'fiO and its solid solutions (Ba,Sr)TiO , (Ba,Pb) fiO , Ba(Sn,Ti)0,, Ba(Zr,Ti)0 and PbTiQ and its solid solutions (PZT), as determined by x-ray diffraction patterns, as shown in the accompanying drawings.

Brief description of tiic drawings
l-ig. I x-ray dillraccion paitcrnol I'bl'iO, calcined at diMcrcut temperatures.
I'ig. 2 TG/DTA of as-prepared powder of F'bTiO,.
l-ig. 3 X-ray dilfractioii pattern^ot Pb(Zr„5, ri„5)0., calcined at dillerem temperatures.
i'ig. 4 X-ray dilTractogram of BaTiO, heat treated at differcni temperatures.
Pig. 5 X-ray dilTractogram of (Ba„75,Sr„j,)Ti03 solid solution calcined at different
temperatures. I'ig. 6 Resistivity {p) - Temperature (I) characteristics of (a) n-BaTiO,, (b)
n-(Ba«,7j,Sr„2j)Ti03 and (c) n-(Ba 1000 ml of 'riCl4 (~ 98 % purity) is diluted to 4000 ml in deionised water under ice-cold coiidilioiis lo form titanium oxycliloride (1 iOCIj) solution. I'o this clear solution, about 60-70 ml of concentrated ammonia solution is added to partially precipitate the litania gel. The fractionally formed precipitate carry the itnpurities along with ii. spccilically the leiric ions. I lii
gel \s separated by lilteration and discarded. Tlie process is repealed once again il ihc iniiial iron contem is high (>l %)• Ihc TiO, content in the impurity-tree TilKl, solution is tlicn
0
estimated.
When a solid Is separating out Irom a homogeneous solution as a precipitate, the impurity distributes between the solid formed and the original solution. It the impurities have chemical coherence with one or more elements present in the precipitate, the impurities will be solely present in it, rather than in the solution. In the case of litanates and zirconates, the Impurities are mostly transition tiietal ions (F"e. Mn, Cr. Co and Ni) which have complete cohercticc with the titanium or zirconium so that even the incipiently lornied piecipitate tarries most of Ihc Impurities. The present invention makes use of this principle.
(b) Barium Chloride (IJaClj .211,0)
500 g of liaCI, .211,0 ( ~ 98 % purity, l.aboialory Rcageni tirade) is dissolved in 1.5 litres of dcionised water. To this solution, 500 ml of conceniralcd hydrochloric acid (35 wt %) is added till all the barium chloride is precipitated, leaving all the impurities in the Strongly acidic solution. Precipitation occurs because of the coimiion ion effect. I he precipitate is washed free of hydrogen chloride using ethyl alcohol and dried at I20"C.
(c) Uad Nitrate IPblNOj)^]
500 g of lead nitrate ( ~ 98 % purity, Uiboralory Reagent Grade) is dissolved in about 2 litres of deionised water. To this solution, 500 ml of concentrated nitric acid is added so that lead nitrate precipitates by common ion effect. The impurities are left behind in the strongly acidic solution. The precipitate is then washed with disiilled,cthyl alcohol, till it is free of nilric acid and dried at 120"C for 6 h.

(di Zirconium Oxychloride (ZrOClj)
500 g of ZrOCI, is dissolveci in about 2 litres ol cicioniscci water. I o this is added ammonia lo Iraciionally precipiiat'e zirconia gel wliich carries away all the impurities. The gel is then filtered and discarded. The impurity tree ZrOCI, solution is the.i made use of for the preparation of perovskiie solid solutions. Example 1
Lead TItanate (PbTiOj)
To 1330 ml of pure TiOCI, solution containing 262 gins of TiO,, about 1000 ml of concentrated ammonia solution is added to precipitate the titania gel at 30-40"C (pli is maimaitied at - 8). The gel is washed free of the chloride ions and ammonium ions. The chloride free gel is (hen dissolved In 1000 ml of concentrated nitric acid diluted to 4(KK) ml. Hie
mixture has to be preserved for 4 h to obtain clear solution. To the clear solution of (itanyl nitrate, 1100 gms of lead nitrate (purified) is added and fractionally coprecipitated by the addition of 130 ml of amtjionium carbonate. The |)rccipitalc is then removed by liltraiion and discarded. 6400 ml of ammonium carbonate { ~ 2M coiicciitralioii) is then added to the purified solution at 30-40*'C (pll is maintained at ~ 8). resulting in a precipitate containing lead carbonate particles embedded in hydrated titania gel. The precipitate is washed free ol the nitrate and ammoniuin iotts. It is then homogenised in deioni,sed water or ethyl alcohol medium. u The x-ray diffraction pattern of the powders calcined at different temperatures
r
are shown in l-ig. I. Ihe x-ray diffractogram of the as-prepared powder dried at I20"C for 10 h showed the presence of lead carbonate (PbCXJ,) as (he ciystalline phase. No titanium

.dioxide (TiO ) is detected since it is in the amorphous form by way of hydrated titania. Heat treatment of the powder at - 275 degree C. for 4 h, results in the formation of PbO with tetragonal symmetry, whereas no rctlections of TiO^ (neither anatase nor rutile) are observed. On calcining at 350 degree C for 4 h, x-ray reflections of PbO (tetragonal) and Pb^TijD^ of defect pyrochlore structure are observed. When the duration of calcination at 350 degree C is extended to more than 12 h, the intensities of the reflection from Pb^^TiJI)^ has increased. The formation of the defect pyrochlore, Pb.Ti 0_ , where x=L is reported in literature from the borosilicate glass matrix containing"lead and titanium dioxide (16). This defect pyrochlore dphase has the same composition as that oJ" the pcrovskite. although it has a different crystal structure. As the calcination temperature is mcreased above 350 degree C, reflections of PbO (tetragonal) shifts to larger 20-values, indicative of the decreased d - spacings as well as the cell parameters. This arises from the partial dissolution of TiO in PbO (tetragonal) to form a solid
I

solution, designated as |(l>b0.xTiO,),J. Thus at the calcination temperature ol 40()'X^ lor 4 h. x-ray rellections of PbTiO^ (perovskite), PbO.xTiO, (0 Thermoanalytica! results (IG/DTA) of the as picpatcd powder (lig. 2) shows (lie weight loss in three steps: (i) below lOOT (~ 6 %), due to the loss of free 11,0 retained in the solid, (ii) around 260"C (~ 4 %), corresponding to the decomposition of VhCO, and (iii) around 300-320T ( ~ 2.5 %), due to the reaction ol amorphous hydroxylated tiiania with PbO accompanied by the release of water due to dehydroxylation. I here is little weight loss above 350"C (~ 0.5 %). The corresponding endoiliernjs are observed around ()()"(', 255"(" and 3()()"C (Pig. 2) in the TG/DTA curves.

The powders prepared are Irigl.ly reailive hccaiise ,>f .he low .emperalurc ol formation of the product. The product-yield is nbearly quantitave. 98 % Highly crystalline
and phase pure powders are obtained. Example 2
Lead zirconium titaiiate (PZT)
To a solution containing 1^50 ml of TiOCI^ (containing 246 gms of TiO,) and 993 gms of ZrOCIj. about 1000 ml of concentrated ammonia solution is added to precipitate the hydroxides of titaniutn and zirconium. The gel is washed tree of chloride and ammonium ions using deionised water. It is then dissolved in 1250 ml of concentrated nitric acid diluted to 3750 ml, by allowing to stand for 6 hours. To the clear solution of tiiaiiyl zirconyl nitrate. 2040 gms of lead nitrate is added and fractionally coprecipilated by the addition of 300 ntl ot ammonium carbonate of 2 M conceiuration. The prccipilalc is removed by lillralion. To ihc puritied solution, 6000 ml of annnonium carbonate ( ~ 2M) is added al 30 40"(' (pi I nuiiniaincd at ~ 8) to form the composite precipitate. The precipitate is washed free of nitrate and ammonium ions. It is then homogenised in deionised water or ethyl alcohol medium lor an hour, using a magnetic stirrer having teflon coated paddle and dried at I20"(^ for 10 h. I'iiis is followed by the calcination step at elevated temperatures, as in l-xatnple I.
Fig. 3 shows the x-ray diffraction pattern of the powders calcined at different temperatures. The as-prepared powder (dried at I2()"(:) showed the presence of the crystalline lead carbonate phase. Heat treatment at 400"C for 4 h results in tfie formation of the mixed phases namely, perovskite |Pb(Zru5,Tio5)03)|(I'ZT), PbO and the defect pyrochlore phase |(Pb,(Zr„5,Ti„5)jOJ. Further annealing at 45()"C for 24 h results in the evolution of a crystalline phase of the perovskite.

'Example 3
Barium titanate (BaliOj)
The procedure described in Example 1 is followed. The starting reaction mixtures are; purified aqueous titanyl chloride and barium chloride. 1070 gms of this soluble salt of barium is dissolved in 1740 ml of titanium oxychloride solution (containing 343 gms of TiO,) and were fractionally coprecipitated by the addition of 170 ml of ammonium carbonate of 2 M concentration. The precipitate is removed by filtration. 8350 ml of ammonium carbonate (- 2M concentration) is then added to the purified solution at 30-40"C (with the pM maintained at ~ 8), to coprccipitatc the carbonate of barium alongwith the hydraied tiiania. The precipitate is (hen washed free of chloride and ammonium ions. It is then homogenised in deioniscd water or distilled ethyl alcohol medium for about an hour and then dried at I20"C' for about 10 h. This is lollowed by calciiialioii at elevated temperatures.
The x-ray diffraction pattern of the as-prepared powder dried at I2()"C tor 10 h, showed the presence of BaCOj. No x-ray reflections of TiO, is observed, indicating that it is present as hydrated titania gel which is x-ray amorphous. Meat treatment at 450T for 4 h,showed the persistence of only the carbonate phase. Further annealing at 650"C' resuhed in the formation of mixed phases namely, the major phase was that of the perovskiie (Ma liO,) and the minor phase corresponding to the defect Ba-pyrochlore (Bajl i,OJ. At temperatures -800'C. )hase pure and highly crystalline phase of the perovskite, i.e. BaTiOj is obtained. The amount f powder obtained is around 1000 gms, corresponding to ~ 98 % yield. The impurity contents
I the resulting powders were determined by atomic absorption, spectrometry and the total
incentrations of Fe, Co, Ni, Mn and Cr were less than 20 ppm.

Example 4
Solid solutions of BaTiO3
1840 ml of titanium oxychloride (containing - 362 gms of TiC2) is diluted to 2 litres in deionised water. To this, 830 gms of BaCI^ .2H^J and 302 gms of SrCl ^ .6H^0 were added and fractionally co-precipitated along with titania by the addition of 180 ml of ammonium carbonte (2M). The precipitate is removed by filtration and discarded, To this purified solution, about 8850 ml of ammonium carbonte (- 2M concentration) is added at 30-40 degree C (pH is maintained at -8) to form the composite precipitate. The precipitate is washed free of chloride and ammonium ions. It is then homogenised by constant stirring in deionised water or ethyl alcohol medium and dried at 120 degree C for 10 h. The resultant powder was flowing. The powder was then calcined at elevated temperatures ( 800 degree C) to give the resultant crystalline phase of (Ba , Sr )TiO. The mass of the product obtained is - 1000 gms.
Fig. 5 shows the x-ray diffraction pattern of (Ba , Sr ,)TiO . The x-ray diffractogram of the as - prepared powder (dried at 120 degree C) shows the presence of BaCO^, SrCO^ phases along with the amorphous hydrated TiO . Heat treatment at 650 degree C for 6 h showed the persistence of the mixed phases, the major phase being that of the perovskite and the minor

phase corresponding to the defect pyroclilorc. Further heat ireat.ncnt at ~ 800°C or 6 h leads to a crystalline phase pure solid solution. The cell parameter (a) calculated lo be 3.97 A agrees well with the reported values 117]. The method is extended lor the preparation ot (Ba,,. Srj IKJ (where x = 0 to 1) by varying the Ba/Sr ratios in the precipitation.
Various other solid solutions of perovskites were prepared by the above procedure. They are listed below:
(a) (Ba,.„PbjTiO, x = 0 to 0.6
(b) Ba(Sn„Ti,.,)0, x = 0 to 1.0
(c) Ba(Zr„Ti,.,)0, x = Oto 1.0
(d) (Ba,..+,,Sr.,Cay)TiO, x = 0 to 0.5, y = 0 to 0.3
Semiconducting ceramics based on BaI'iO, and its solid solutions prepared from powders derived from the prescni route are lound to give cxcclleni VVCR (positive temperature cocrticicm ol resistance) characteristics (l-jg. 6), po.s.sibly hccau.sc of the absence o( the alkali. This clearly shows that the products obtained through this route are phase pure.

References
, A.J. Moulson and J.M. Herbert,,Electroceraics, Chaoman & Hall, London, 1990
2. P.P. Phule and S.H. Rlsbud, J. Mater. Sci. 25 (1990) 1169.
3. P. Padmini and T.R.N. Kutty. J, Mater, Sci; Materials in l-lcctroiiics. 5 (1994)
203.
4. K.S. Mazdiyasiii et al. US Patent 3647364, March (1972).
5. K.S. Mazdiyasiii and L.M. Brown, J. Am. Ceram. Soc. 55 (1972) 633.
6. A.N. Christensen, Acta Chem. Scand. 24 (1970) 2447.
7. H. Okada, H. Maisubayaslii and I". Goto, Japanese Patent JP 6272525 A2|87/72425|. March (1987).
8. W.S. Claubaugh. E.M. Swiggard atid R. Gilchrist, J. Res. Nat. Bur. Std. 56 (1956) 289.
9. P.P. Phule and S.ll. Ri.sbud, Mater. Sci. lingg. H3 (I9«9) 241.
10. J.M. Wilson, D.L. Coller and S. Venkalaraniani. US Patent 4670243, June (1987).
11. M. Pechini. US Patent 3330697, July (1967).
12. B.J. Mulder, Ceram. Bull. 49 (1970) 990.
13. S. DiViia and R.J. Fischer, U.S Patent 2985506, May (1961).
14. A.S. Shaikh and G.M. Vest, J. Am. Ceram. Soc. 69 (1986) 682.
15. A. Beauger, J.C. Mutin and J.C. Niepece, J. Mater. Sci. 18 (1983) 304.
16. Martin, Phy. Chem. Glasses, 6 (1965) 143.
17. T.R.N. Kutty and P. Padmini, Mater. Res. Bull. 27 (1992) 945.

We claim:
1. ' A method for the production of perovskite titanate compounds of formula ABO3
w^iere 'A' is divalent and 'B' is tetravalent cation and their solid solutions
comprising:
purifying the starting material of general formula XgYb (where X denotes metal ions Ti, Zr, Ba, Sr, Ca and Pb and 'Y' denotes chlorides or nitrates and a=l and b=2-4, if Y denotes nitrate, X is Pb), by in situ fiactional precipitation involving preferential segregation of impurities into the solid, leading to a pre¬determined impurity contents,
co-precipitating the crystalline hydrated carbonates of Ba, Pb, Ca or Sr along with the hydrated titania, Zirconia or Stannia by the addition of ammonium carbonate at 30-40 degree C to the corresponding chlori(ks or nitrate solution till the pH is 8,
washing the precipitate with water to make it free of the anions (CI or NO3) and ammonium ions,
drying the said precipitate at 100-120 degree C followed by calcination at below 800°C.
2. A method as claimed in claim I wherein the starting materials of general formula are TiCl2, Z1OCI2, BaCLz, SrClz, CaCh, Pb(N03)2.
3. A method as claims in claim 1 wherein the starting material TiQi and ZrOCh are purified by dissolving the said materials separately in deionised water and thereafter adding ammonia to precipitate titania gel and zirconia gel, the fractionally formed precipitate carry the impurities of transition metal ions - Fe, Mn, Cr, Co and Ni.
4. A method as claimed in claim 3 wherein the ammonia used is concentrated ammonia solution.
*5. A method as claimed in claim 1 wherein BaCb is purified by dissolving it in deionised water and HCl is added till the BaCb is precipitated by common ion effect leaving all the impurities in the strongly acidic solution and the precipitate is washed free of HCl using ethyl alcohol and dried at 120 degree C.

6. A method as claimed in claim 5 wherein HCl used in concentrated HCl.
7. A method as claimed in claim 1 wherein Pb(N03)2 is purified by dissolving it in
deionised water and HNO3 is added till Pb(N03)2 is precipitated by common ion
effect and the precipitate then is washed with distilled ethyl alcohol till it is free of
HNO3 and dried at 120 degree C.
8. A method as claimed in claim 7 wherein HNO3 used is concentrated HNO3.
9. A method as claimed in claim 1 wherein said predetermined impurity contents are
around 10 parts per million.
10. A method as claimed in claim 1 wherein solid solutions are (Ba,Sr)Ti03, (Ba,Pb)Ti03,
Ba(Sn,Ti)03, Ba (Zr,Ti)O3 and PZT.
11. A method for the production of perovskite titanate compoimds of formula ABO3
where 'A' is divalent and 'B' is tetravalent cation and their solid solutions
substantially as herein described with reference to the foregoing examples.

Documents:

0363-mas-1996 abstract.pdf

0363-mas-1996 claims.pdf

0363-mas-1996 correspondence others.pdf

0363-mas-1996 correspondence po.pdf

0363-mas-1996 description (complete).pdf

0363-mas-1996 drawings.pdf

0363-mas-1996 form-1.pdf

0363-mas-1996 form-26.pdf

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Patent Number

193110

Indian Patent Application Number

363/MAS/1996

PG Journal Number

35/2005

Publication Date

16-Sep-2005

Grant Date

08-Jul-2005

Date of Filing

08-Mar-1996

Name of Patentee

INDIAN INSTITUTE OF SCIENCE

Applicant Address

BANGALORE-560012

Inventors:

#	Inventor's Name	Inventor's Address
1	THUNDYIL RAMAN NARAYANAN KUTTY	MATERIALS RESEARCH CENTRE INDIAN INSTITUTE OF SCIENCE BANGALORE - 560 012
2	PERIASWAMY PADMINI	MATERIALS RESEARCH CENTRE INDIAN INSTITUTE OF SCIENCE BANGALORE - 560 012

PCT International Classification Number

C01G23/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA