PREPARATION OF LEAD ZIRCONATE (PbZrO3)
BY HOMOGENEOUS PRECIPITATION AND CALCINATION
Researchers: Ersin Emre OREN, Ercan TASPINAR and A. Cüneyt TAS
Department of Metallurgical and Materials Engineering,
* Journal of The American Ceramic Society, Vol. 80, (1997) pp. 2714-2716. (------> download pdf: pz.pdf)
* E.E. Oren, E. Taspinar, and
A.C. TAS, "Chemical Synthesis of Antiferroelectric
Lead Zirconate (PbZrO3) by Homogeneous
Precipitation," III. Ceramics Congress, Proceedings
Book, Vol. 2, pp. 59-65,
Antiferroelectric PbZrO3 has
been synthesized by homogeneous precipitation from aqueous solutions in the
presence of urea (NH2CONH2) and calcination
for 6 hours at 700°C. SEM studies displayed the presence of sub-micron
powder, with a significant degree of agglomeration.
Lead zirconate, PbZrO3, is an antiferroelectric ceramic with a Curie temperature of 230°C. It is reported that the antiferroelectric (AFE) to ferroelectric transition (under the application of a strong electric field to the ceramic in the antiferroelectric state) leads to significant energy storage for DC field. This feature of PbZrO3 makes it a candidate material for energy storage applications (1). Piezoelectric and dielectric properties of lead zirconate thin films, derived from a sol-gel technique, were studied and compared with the most significant piezoelectric compositions (2, 3). PbZrO3 was also searched for its microwave dielectric properties but it shows a dielectric relaxation near microwave frequencies (4). A strong correlation between the lattice defect concentration and dielectric loss at microwave frequencies has also been reported (5, 6). The volatility of Pb species at the temperatures needed to prepare lead zirconate ceramics is believed to be the reason for the relaxation in PbZrO3 phase (4). Therefore, a decrease in the processing temperature of lead zirconate phase may result in an improvement in the final electrical properties of the ceramic part.
Preparation of lead zirconate by conventional processes; that is, mixing and firing of the binary oxides (PbO and ZrO2), requires the use of high temperatures at which PbO volatility also becomes significant. It is reported that the full development of pure PbZrO3 phase occurs after sintering at temperatures above 1200°C for at least 2 hours in controlled PbO atmospheres (4-5,7-8).
Lead zirconate was previously synthesized by a sol-gel method (8), which necessitated the use of complex processing practices and a strict control of many process parameters, such as pH of the solutions, temperature, and concentrations of the cations. For the sol-gel method, the calcination temperature to yield pure PbZrO3 was reported to be as low as 700°C for 6 hours of soaking time (8). The phase formation temperature for pure PbZrO3, by the citrate route, was also reported to be in the vicinity of 700°C (9).
In the present study, the experimental details and results of the synthesis of the lead zirconate phase from water soluble salts of Pb and Zr (chlorides) by homogeneous precipitation via urea decomposition are presented. The decomposition of urea in aqueous solutions is accompanied by the slow and controlled supply of ammonia and carbon dioxide into the solution . The smooth pH increase obtained by the decomposition of urea, in unison with the steady supply of OH- and CO32- ions, typically lead to the precipitation of metal hydroxycarbonates of controlled particle morphology [11-13]. Homogeneous precipitation from aqueous solutions, in the presence of urea, have been used to produce disperse spherical particles of basic lanthanide carbonates , cerium oxide , Y3Al5O12 , and LaAlO3 . In this study, homogeneous precipitation techniques, similar to those described in the literature (11-17), were employed and shown to be successful for the preparation of phase-pure PbZrO3 after calcination at 700°C.
The below XRD diagram shows the crystallization behavior of the hydroxycarbonate precursors of the PZ phase as a function of increasing calcination temperature.
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