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Synthesis of ultra-fine crystalline ZrxTi1 − xO4 powder by polymeric precursor method
February 1995
MaterialsLetters22
ELSEVIER
(1995) 181-185
Synthesis of ultra-fine crystalline Zr,Ti 1_-xO4powder by polymeric precursor method M. Cerqueira a, R.S. Nasar a, E. Long0 a, E.R. Leite ‘, J.A. Varela b ’ Departamentode Quimica, UFSCar, &io Carlos,SP, 13565-905, Brazil b Institutede Quimica, UNESP,Araraquara,SP, 14800-900, Brazil Received 11 October 1994; accepted 15 October 1994
AhStlN!t Reactive Zr,Ti, _& (x=0.65, 0.50 and 0.35) powder was prepared by the polymeric precursor method. Studies by X-ray diffraction (XRD), nitrogen adsorption/desorption, and thermogravimetric analysis (TG) showed that powders with high crystallinity ( > 90%) and high surface areas ( > 40 m*/g) are obtained after calcination at 700°C for 3 h. Infrared spectroscopy and XRD results showed that these titanates nucleate from the amorphous phase with no intermediate phases, at low temperature (45OOC).
1. Introduction Zirconium titanate (ZT) is a well-known material used in many industrial applications. It is used as a dielectric material for its low dielectric loss in telecommunication and microwave devices [ 11, in catalysis [ 2 ] and as a precursor for synthesis of lead zirconium titanate (PZT) [ 3,4]. The use of ZT with different stoichiometry, as a precursor for synthesis of PZT by the partial oxalate method [ 3,4], allows control of PZT stoichiometry. However, to obtain tine and sinterable PZT powders by the partial oxalate method, it is necessary to use fine and single phase ZT powder [ 41. Otherwise the use of the conventional solid state reaction between TiOz and ZrOz needs high temperatures ( > 1200°C) to reach a single ZT phase, resulting in agglomerated and low reactive powders [ 5 1. Hence, it becomes necessary to use non-conventional methods for the synthesis of crystalline ZT powder at low temperatures. Navio at al. [6] reported the synthesis of ZT at 650°C by using the co-precipitation method of hy-
droxoperoxo compound of Zr and Ti, and more recently Bhattacharya et al. [ 71 described a method to obtain ZT powders by sol-gel route where the ZT crystalline phase is formed at 400°C. In this work, the use of the polymeric precursor method [ 81 for the synthesis of Zr,Ti,_,O, (x=0.65; 0.50 and 0.35) is described, in order to obtain very tine and single-phase ZT powders to be used as precursors for synthesis of PZT piezoelectric powders.
2. Experimental procedures 2.1. Synthesis The materials used for synthesis of Zr,Tii _,O, as well as their origin are shown in Table 1. From titanium isopropoxide and zirconium n-propoxide, citrate solutions were prepared at concentrations of 0.0733 g of TiOz per gram of Ti citrate solution and 0.0699 g of ZrOz per gram of Zr citrate solution. These citrate solutions were mixed considering the stoichi-
0167-577x/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOl67-577x(94)00228-2
182
M. Cerqueira et al. /Materials Letters 22 (1995) 181-185
Table 1 Materials used in the synthesis of ZT Material
Origin
titanium isopropoxide zirconium N-propoxide citric acid ethylene glycol
Huls AC, Germany Aldrich Chem. Company, USA E. Merck, Germany E. Merck, Germany
ometry Zr,Ti,_,O,, forx=0.65,0.50 and 0.35. After solution homogenization, ethylene glycol was added at a mass ratio of 40160 in relation to citric acid. These solutions were polymerized at 300°C for 2 h. The resulting polymer was ground in a ball mill, calcined for 3 h at various temperatures and then characterized. 2.2. Characterization 2.2. I. X-ray difliaction (XRD) The powders calcined at different temperatures
were characterized by X-ray diffraction, using a Siemens diffractometer with Cu Ko radiation (Model D-5000) and graphite monochromator. To determine crystallinity, a calibration curve of the concentration of crystalline material as a function of X-ray intensity was used. In this study, the material calcined at 1000°C for 3 h was considered to be 100% crystalline and the polymeric precursor polymerized at 300°C was considered to be 100% amorphous. The ZT peak at 28~ 37.0 was used to calculate the X-ray integrated intensity. 2.2.2. Surface area and porosity measurements The measurements of surface areas and pore size distributions of the calcined powders were performed on a Micromeritics ASAP 2000 using Nz as the adsorption/desorption gas. To determine the surface area the BET method was used and to determine pore size distribution the BJH method [ 9 ] considering the desorption curves was used. Samples were degassed at 250°C for 2 h prior to each analysis.
infrared spectroscopy (FTIR), using the KBr pellets technique. 2.2.4. Thermal analysis Thermogravimetric analysis (TG) of the samples was carried out using an STA 409 (Netszch) in synthetic air up to 1200°C and a heating rate of S”C/min.
3. Results and discussion 3.1. Phase formation Fig. 1 shows the thermogravimetric analyses of the ZT polymeric precursors (x= 0.65 ) , polymerized at 300°C. This thermogram shows a continuous weight loss up to 600°C. Weight loss was not observed for temperatures higher than 600°C indicating that all organic material was decomposed. Similar thermograms were observed for other compositions, i.e. for x=0.50andx=0.35. A diffuse XRD pattern of the ZT polymeric precursor powder, for composition Zr,Ti, _,O, where x=0.5, can be seen in Fig. 2, indicating amorphous material. At 450°C the XRD pattern shows a broad peak at 2t?= 37” indicating nucleation of the ZT phase. At this temperature there is still a large amount of organic material, as can be seen in Fig. 1. With increasing calcination temperature, an increase in ZT crystallinity is observed. A well-resolved XRD pattern for ZT appears at 600°C that coincides with the total weight loss. A similar behavior is observed for compositionswithx=0.35andx=0.65. Forthestoi5 o-5 -1Om -15 z -2om Rote=5oC/nin.
-25 -3om
2.2.3. Infrared spectroscopy (FTIR) Characterization of the polymeric precursors as well as analysis of the intermediate compound during the thermal decomposition process were carried out by
-35 -40,
0
1 100
200
I 300
i
400 500 Temperature
600 (CC)
700
800
900
II 3i10
Fig. 1. Thermogravimetricanalysis of Zr,T&_,O, for x=0.65.
hi. Cerqueiraet al. /Materials Letters 22 (1995) 181-185
Fig. 2. X-ray diffraction pattern at different temperatures for the Zr,Ti,_,O,
chiometry rich in ZrOz or in Ti02 the presence of free oxides was not observed, indicating a perfect solid solution for these stoichiometries. These results are in agreement with k’amaguchi and Mogi [ 14 1, who reported ZrTi04 single phase at low temperatures between 30 and 70 mol% TiOz. Fig. 3 shows the infrared spectra forx=0.65, x=0.5 and x=0.35, in the range 1780 and 1140 cm-‘. For the polymeric precursor, polymerized at 3OO”C,vibrations at 17 10 cm-i were observed, related to the C=O stretching mode for ester groups (R-COO-R). These groups are formed during the polyesterification reaction between ethylene glycol and citrates. Strong vibrations are also observed at 1582 and 1409 cm-‘. These vibrations are related to cation coordination by carboxylic group in the form of bidentate complex. After thermal decomposition at 450 and 550°C no vibrations in the region of 17 10 cm- ‘, relative to ester groups, were observed. The spectra at these temperatures show strong vibrations at 1620 cm-’ indicating the gradual change in the coordination of the metallic cations of the COO- group from bidentate to monodentate complex. No vibrations are observed in the region of 1400 cm-’ related to carbonate groups (CO:- ). The presence of carbonate phases is common in the synthesis of alkaline earth metal titanates by the polymeric precursor method [ 10,111. The absence of these carbonate groups is in agreement with X-ray diffraction data, where no formation of any crystalline intermediate phases was observed, in the range 450 to 55o”C, only the ZT phase. Fig. 4 shows the crystallinity (a) and the variation of surface area (S) as a function of temperature for
183
system for x=0.5.
X-O.65
PolymericPlwwsol
,
.
.
. lo
1
Wnvenumber(cm”) Fig. 3. Infrared spectra for the polymeric precursors treated at differenttemperatures. (1) 171Ocm-‘; (2) 162Ocm-‘; (3) 1582 cm-‘; (4) 1409 cm-‘.
ZT in the three stoichiometries considered. It is observed that for a stoichiometry rich in Zr02 or Ti02 the crystallization starts earlier when compared to the
184
M. Cerqueira et al. /Materials Letters 22 (1995) 181-185
i 120
100 80
S
(m’/g) 00
_i_ 350
450
550
850
750
Temperature
850
050
0 1050
( “0
3.3. General discussion
Fig. 4. Crystallinity ((r) and surface area (S) as a function of temperature for the Zr,Ti,_,O, systems (x=0.50,0.65,0.35). Table 2 Physical characteristics of the precursors calcined at 700°C for 3 II Stoichiometry (Zr,Ti,-A)
Crystallinity W)
Surface area (m*/g)
Pore volume (cm3/g)
x=0.65
97 86 94
41.6 33.8 41.3
0.111 0.068 0.075
x=0.50 x=0.35
Analysis of the nitrogen adsorptionldesorption hysteresis curves for the precursor powders calcined at 700°C indicates the presence of open pores of cylindrical geometry [ 12 1. Pore size distribution curves obtained by the BJH method (Fig. 5 ) indicate a narrow and monodisperse distribution with mean pore size of about 3 to 8 nm, depending on the powder stoichiometry. The total pore volume described in Table 2 indicates a structure of agglomerated particles with low porosity.
stoichiometric ZT (x= 0.50). This indicates that the excess of metallic cations probably act as a nucleation agent for this titanate. A gradual decrease in surface area with increase of temperature is also observed in Fig. 4, indicating gradual particle growth. The XRD, FTIR and TG analyses showed that the ZT phase was formed at low temperature (45O”C), with no intermediate phase. The reaction was complete at 6OO”C,above which an increase in crystallinity should be due to crystallite growth.
Recent papers in the literature on the synthesis of ZT are based on the sol-gel method where the titanium and zirconium salts are chlorides [ 6,7 1. Preparation techniques of titanates that involve the preparation of gel in basic pH can promote the formation of TiOz.xHzO agglomerates, due to a rapid condensation reaction between Ti-OH groups [ 13 1. This can lead to the segregation of Ti4+ ions promoting the formation of free TiOz during the calcining process, as observed by Navio et al. [ 61. In the polymeric precursor method this problem is avoided because the ions are chelated by organic groups (citrates). The homogenization of citrate solutions in the liquid phase allows mixing of cations at a molecular level. With the addition of ethylene glycol polymerization is promoted, forming a translucent and single phase solid, with no segregation. Further decomposition of the organic phase leads to ion oxidation and the ZT phase formation at low temperature (about 45O”C), due to the small distance between the interdiffusing ions.
3.2. Powder morphology Table 2 shows the surface area and crystallinity of polymeric precursors calcined at 700°C for Zr,Ti,_,O, (x=0.65, x=0.50 and x=0.35). A high surface area and high crystallinity for the ZT powders are observed. Brattacharya et al. [7] reported high crystallinity for ZT calcined at 400°C synthesized by the sol-gel method, but with a surface area of 9.2 m2/g. These results show that although the polymeric precursor method needs high temperature to obtain high crystallinity, the powders are very fine and reactive.
10
Pore Diameter (rim) Fig. 5. Pore size distributions for the precurso rs calcined at 700°C for 3 h.
h4. Cerqueiraet al. /Materials Letters22 (1995) 181-185
4. Conclusions
185
References [ 1] R.C. Buchana, Ceramic materials for electronics (Dekker,
The synthesis of Zr,Ti,_,O, (x=0.65, 0.50 and 0.35) by the polymeric precursor method allows the formation of very fine and single phase particles with high surface area and crystallinity. Thermal decomposition studies of precursors show that the ZT phase nucleates directly from the amorphous precursors with no intermediate phase. The ZT powders obtained by this method have agglomerates with low porosity. These results indicate that the ZT powders prepared by the polymeric precursor method may be used as a precursor in the synthesis of PZT by the partial oxalate method.
Acknowledgement The authors acknowledge CNPq, FINEP/PADCT and FAPESP, all Brazilian agencies, for the financial support of this work
New York, 1986) p. 154.
[ 21 K. Araka and K. Tanabe, Bull. Chem. Sot. Japan 53 ( 1980) 299.
[ 31 T. Yamamoto, Am. Ceram. Sot. Bull. 7 1 ( 1992) 978. [4] E.R. Leite, E. Longo, M.C. Cavaco, L.C. Carvalho, J. Avena and J.A. Varela, Proceedings of Third Euro-Ceramics, Vol. 1 (Faenza Editrice Iberica S.L., 1993) p. 309. [5]R.W.LynchandB.Monison,J.Am.Ceram.Soc.55 (1972) 409. [6] J.A. Navio, F.J. Marchena, M. Macias and P.J. SanchezSoto, J. Mater. Sci. 27 (1992) 2463. [ 71 AK. Bhattachatya, K.K. Mallick, A. Hartridge and J.L. Woodhead, Mater. Letters 18 ( 1994) 247. [8] M. Pechini, U.S. Patent no. 3.330.697 (1967). [ 91 Operation Manual - ASAP 2000, Micromeretics Instrument Corp. Nocross, GA ( 199 1). [ lo] S. Kumar, G.L. Messing and W.B. While, J. Am. Ceram. Sot. 76 (1993) 617. [ 111 E.R. Leite, C.M.G. Souza, E. Long0 and J.A. Varela, Ceram. Intern.,to be published ( 1994). [ 121 K.S.W. Sing, Pure Appl. Chem. 54 (1982) 2201. [ 13 ] F. Chaput, J.P. Boilot and A. Beauger, J. Am. Ceram. Sot. 73 (1990) 942. [ 1410. Yamaguchi and H. Magi, J. Am. Ceram. Sot. 772 (1989) 1065.
MaterialsLetters22
ELSEVIER
(1995) 181-185
Synthesis of ultra-fine crystalline Zr,Ti 1_-xO4powder by polymeric precursor method M. Cerqueira a, R.S. Nasar a, E. Long0 a, E.R. Leite ‘, J.A. Varela b ’ Departamentode Quimica, UFSCar, &io Carlos,SP, 13565-905, Brazil b Institutede Quimica, UNESP,Araraquara,SP, 14800-900, Brazil Received 11 October 1994; accepted 15 October 1994
AhStlN!t Reactive Zr,Ti, _& (x=0.65, 0.50 and 0.35) powder was prepared by the polymeric precursor method. Studies by X-ray diffraction (XRD), nitrogen adsorption/desorption, and thermogravimetric analysis (TG) showed that powders with high crystallinity ( > 90%) and high surface areas ( > 40 m*/g) are obtained after calcination at 700°C for 3 h. Infrared spectroscopy and XRD results showed that these titanates nucleate from the amorphous phase with no intermediate phases, at low temperature (45OOC).
1. Introduction Zirconium titanate (ZT) is a well-known material used in many industrial applications. It is used as a dielectric material for its low dielectric loss in telecommunication and microwave devices [ 11, in catalysis [ 2 ] and as a precursor for synthesis of lead zirconium titanate (PZT) [ 3,4]. The use of ZT with different stoichiometry, as a precursor for synthesis of PZT by the partial oxalate method [ 3,4], allows control of PZT stoichiometry. However, to obtain tine and sinterable PZT powders by the partial oxalate method, it is necessary to use fine and single phase ZT powder [ 41. Otherwise the use of the conventional solid state reaction between TiOz and ZrOz needs high temperatures ( > 1200°C) to reach a single ZT phase, resulting in agglomerated and low reactive powders [ 5 1. Hence, it becomes necessary to use non-conventional methods for the synthesis of crystalline ZT powder at low temperatures. Navio at al. [6] reported the synthesis of ZT at 650°C by using the co-precipitation method of hy-
droxoperoxo compound of Zr and Ti, and more recently Bhattacharya et al. [ 71 described a method to obtain ZT powders by sol-gel route where the ZT crystalline phase is formed at 400°C. In this work, the use of the polymeric precursor method [ 81 for the synthesis of Zr,Ti,_,O, (x=0.65; 0.50 and 0.35) is described, in order to obtain very tine and single-phase ZT powders to be used as precursors for synthesis of PZT piezoelectric powders.
2. Experimental procedures 2.1. Synthesis The materials used for synthesis of Zr,Tii _,O, as well as their origin are shown in Table 1. From titanium isopropoxide and zirconium n-propoxide, citrate solutions were prepared at concentrations of 0.0733 g of TiOz per gram of Ti citrate solution and 0.0699 g of ZrOz per gram of Zr citrate solution. These citrate solutions were mixed considering the stoichi-
0167-577x/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOl67-577x(94)00228-2
182
M. Cerqueira et al. /Materials Letters 22 (1995) 181-185
Table 1 Materials used in the synthesis of ZT Material
Origin
titanium isopropoxide zirconium N-propoxide citric acid ethylene glycol
Huls AC, Germany Aldrich Chem. Company, USA E. Merck, Germany E. Merck, Germany
ometry Zr,Ti,_,O,, forx=0.65,0.50 and 0.35. After solution homogenization, ethylene glycol was added at a mass ratio of 40160 in relation to citric acid. These solutions were polymerized at 300°C for 2 h. The resulting polymer was ground in a ball mill, calcined for 3 h at various temperatures and then characterized. 2.2. Characterization 2.2. I. X-ray difliaction (XRD) The powders calcined at different temperatures
were characterized by X-ray diffraction, using a Siemens diffractometer with Cu Ko radiation (Model D-5000) and graphite monochromator. To determine crystallinity, a calibration curve of the concentration of crystalline material as a function of X-ray intensity was used. In this study, the material calcined at 1000°C for 3 h was considered to be 100% crystalline and the polymeric precursor polymerized at 300°C was considered to be 100% amorphous. The ZT peak at 28~ 37.0 was used to calculate the X-ray integrated intensity. 2.2.2. Surface area and porosity measurements The measurements of surface areas and pore size distributions of the calcined powders were performed on a Micromeritics ASAP 2000 using Nz as the adsorption/desorption gas. To determine the surface area the BET method was used and to determine pore size distribution the BJH method [ 9 ] considering the desorption curves was used. Samples were degassed at 250°C for 2 h prior to each analysis.
infrared spectroscopy (FTIR), using the KBr pellets technique. 2.2.4. Thermal analysis Thermogravimetric analysis (TG) of the samples was carried out using an STA 409 (Netszch) in synthetic air up to 1200°C and a heating rate of S”C/min.
3. Results and discussion 3.1. Phase formation Fig. 1 shows the thermogravimetric analyses of the ZT polymeric precursors (x= 0.65 ) , polymerized at 300°C. This thermogram shows a continuous weight loss up to 600°C. Weight loss was not observed for temperatures higher than 600°C indicating that all organic material was decomposed. Similar thermograms were observed for other compositions, i.e. for x=0.50andx=0.35. A diffuse XRD pattern of the ZT polymeric precursor powder, for composition Zr,Ti, _,O, where x=0.5, can be seen in Fig. 2, indicating amorphous material. At 450°C the XRD pattern shows a broad peak at 2t?= 37” indicating nucleation of the ZT phase. At this temperature there is still a large amount of organic material, as can be seen in Fig. 1. With increasing calcination temperature, an increase in ZT crystallinity is observed. A well-resolved XRD pattern for ZT appears at 600°C that coincides with the total weight loss. A similar behavior is observed for compositionswithx=0.35andx=0.65. Forthestoi5 o-5 -1Om -15 z -2om Rote=5oC/nin.
-25 -3om
2.2.3. Infrared spectroscopy (FTIR) Characterization of the polymeric precursors as well as analysis of the intermediate compound during the thermal decomposition process were carried out by
-35 -40,
0
1 100
200
I 300
i
400 500 Temperature
600 (CC)
700
800
900
II 3i10
Fig. 1. Thermogravimetricanalysis of Zr,T&_,O, for x=0.65.
hi. Cerqueiraet al. /Materials Letters 22 (1995) 181-185
Fig. 2. X-ray diffraction pattern at different temperatures for the Zr,Ti,_,O,
chiometry rich in ZrOz or in Ti02 the presence of free oxides was not observed, indicating a perfect solid solution for these stoichiometries. These results are in agreement with k’amaguchi and Mogi [ 14 1, who reported ZrTi04 single phase at low temperatures between 30 and 70 mol% TiOz. Fig. 3 shows the infrared spectra forx=0.65, x=0.5 and x=0.35, in the range 1780 and 1140 cm-‘. For the polymeric precursor, polymerized at 3OO”C,vibrations at 17 10 cm-i were observed, related to the C=O stretching mode for ester groups (R-COO-R). These groups are formed during the polyesterification reaction between ethylene glycol and citrates. Strong vibrations are also observed at 1582 and 1409 cm-‘. These vibrations are related to cation coordination by carboxylic group in the form of bidentate complex. After thermal decomposition at 450 and 550°C no vibrations in the region of 17 10 cm- ‘, relative to ester groups, were observed. The spectra at these temperatures show strong vibrations at 1620 cm-’ indicating the gradual change in the coordination of the metallic cations of the COO- group from bidentate to monodentate complex. No vibrations are observed in the region of 1400 cm-’ related to carbonate groups (CO:- ). The presence of carbonate phases is common in the synthesis of alkaline earth metal titanates by the polymeric precursor method [ 10,111. The absence of these carbonate groups is in agreement with X-ray diffraction data, where no formation of any crystalline intermediate phases was observed, in the range 450 to 55o”C, only the ZT phase. Fig. 4 shows the crystallinity (a) and the variation of surface area (S) as a function of temperature for
183
system for x=0.5.
X-O.65
PolymericPlwwsol
,
.
.
. lo
1
Wnvenumber(cm”) Fig. 3. Infrared spectra for the polymeric precursors treated at differenttemperatures. (1) 171Ocm-‘; (2) 162Ocm-‘; (3) 1582 cm-‘; (4) 1409 cm-‘.
ZT in the three stoichiometries considered. It is observed that for a stoichiometry rich in Zr02 or Ti02 the crystallization starts earlier when compared to the
184
M. Cerqueira et al. /Materials Letters 22 (1995) 181-185
i 120
100 80
S
(m’/g) 00
_i_ 350
450
550
850
750
Temperature
850
050
0 1050
( “0
3.3. General discussion
Fig. 4. Crystallinity ((r) and surface area (S) as a function of temperature for the Zr,Ti,_,O, systems (x=0.50,0.65,0.35). Table 2 Physical characteristics of the precursors calcined at 700°C for 3 II Stoichiometry (Zr,Ti,-A)
Crystallinity W)
Surface area (m*/g)
Pore volume (cm3/g)
x=0.65
97 86 94
41.6 33.8 41.3
0.111 0.068 0.075
x=0.50 x=0.35
Analysis of the nitrogen adsorptionldesorption hysteresis curves for the precursor powders calcined at 700°C indicates the presence of open pores of cylindrical geometry [ 12 1. Pore size distribution curves obtained by the BJH method (Fig. 5 ) indicate a narrow and monodisperse distribution with mean pore size of about 3 to 8 nm, depending on the powder stoichiometry. The total pore volume described in Table 2 indicates a structure of agglomerated particles with low porosity.
stoichiometric ZT (x= 0.50). This indicates that the excess of metallic cations probably act as a nucleation agent for this titanate. A gradual decrease in surface area with increase of temperature is also observed in Fig. 4, indicating gradual particle growth. The XRD, FTIR and TG analyses showed that the ZT phase was formed at low temperature (45O”C), with no intermediate phase. The reaction was complete at 6OO”C,above which an increase in crystallinity should be due to crystallite growth.
Recent papers in the literature on the synthesis of ZT are based on the sol-gel method where the titanium and zirconium salts are chlorides [ 6,7 1. Preparation techniques of titanates that involve the preparation of gel in basic pH can promote the formation of TiOz.xHzO agglomerates, due to a rapid condensation reaction between Ti-OH groups [ 13 1. This can lead to the segregation of Ti4+ ions promoting the formation of free TiOz during the calcining process, as observed by Navio et al. [ 61. In the polymeric precursor method this problem is avoided because the ions are chelated by organic groups (citrates). The homogenization of citrate solutions in the liquid phase allows mixing of cations at a molecular level. With the addition of ethylene glycol polymerization is promoted, forming a translucent and single phase solid, with no segregation. Further decomposition of the organic phase leads to ion oxidation and the ZT phase formation at low temperature (about 45O”C), due to the small distance between the interdiffusing ions.
3.2. Powder morphology Table 2 shows the surface area and crystallinity of polymeric precursors calcined at 700°C for Zr,Ti,_,O, (x=0.65, x=0.50 and x=0.35). A high surface area and high crystallinity for the ZT powders are observed. Brattacharya et al. [7] reported high crystallinity for ZT calcined at 400°C synthesized by the sol-gel method, but with a surface area of 9.2 m2/g. These results show that although the polymeric precursor method needs high temperature to obtain high crystallinity, the powders are very fine and reactive.
10
Pore Diameter (rim) Fig. 5. Pore size distributions for the precurso rs calcined at 700°C for 3 h.
h4. Cerqueiraet al. /Materials Letters22 (1995) 181-185
4. Conclusions
185
References [ 1] R.C. Buchana, Ceramic materials for electronics (Dekker,
The synthesis of Zr,Ti,_,O, (x=0.65, 0.50 and 0.35) by the polymeric precursor method allows the formation of very fine and single phase particles with high surface area and crystallinity. Thermal decomposition studies of precursors show that the ZT phase nucleates directly from the amorphous precursors with no intermediate phase. The ZT powders obtained by this method have agglomerates with low porosity. These results indicate that the ZT powders prepared by the polymeric precursor method may be used as a precursor in the synthesis of PZT by the partial oxalate method.
Acknowledgement The authors acknowledge CNPq, FINEP/PADCT and FAPESP, all Brazilian agencies, for the financial support of this work
New York, 1986) p. 154.
[ 21 K. Araka and K. Tanabe, Bull. Chem. Sot. Japan 53 ( 1980) 299.
[ 31 T. Yamamoto, Am. Ceram. Sot. Bull. 7 1 ( 1992) 978. [4] E.R. Leite, E. Longo, M.C. Cavaco, L.C. Carvalho, J. Avena and J.A. Varela, Proceedings of Third Euro-Ceramics, Vol. 1 (Faenza Editrice Iberica S.L., 1993) p. 309. [5]R.W.LynchandB.Monison,J.Am.Ceram.Soc.55 (1972) 409. [6] J.A. Navio, F.J. Marchena, M. Macias and P.J. SanchezSoto, J. Mater. Sci. 27 (1992) 2463. [ 71 AK. Bhattachatya, K.K. Mallick, A. Hartridge and J.L. Woodhead, Mater. Letters 18 ( 1994) 247. [8] M. Pechini, U.S. Patent no. 3.330.697 (1967). [ 91 Operation Manual - ASAP 2000, Micromeretics Instrument Corp. Nocross, GA ( 199 1). [ lo] S. Kumar, G.L. Messing and W.B. While, J. Am. Ceram. Sot. 76 (1993) 617. [ 111 E.R. Leite, C.M.G. Souza, E. Long0 and J.A. Varela, Ceram. Intern.,to be published ( 1994). [ 121 K.S.W. Sing, Pure Appl. Chem. 54 (1982) 2201. [ 13 ] F. Chaput, J.P. Boilot and A. Beauger, J. Am. Ceram. Sot. 73 (1990) 942. [ 1410. Yamaguchi and H. Magi, J. Am. Ceram. Sot. 772 (1989) 1065.