Strontium and calcium zirconyl citrates as precursors for the low-temperature synthesis of SrZrO 3 and CaZrO 3 fine powd
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Strontium and calcium zirconyl citrates as precursors for the low-temperature synthesis of SrZrO3 and CaZrO3 fine powders M. Rajendrana) and M. Subba Rao Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India (Received 16 May 1994; accepted 9 June 1997)
Synthesis and the thermal decomposition behavior of new molecular precursors, strontium, and calcium zirconyl citrates are presented. The pathway to the metazirconate formation has been found to proceed through a multistep process. The precursors yield SrZrO3 and CaZrO3 fine powders at temperatures as low as 650 ±C. Physico-chemical, spectroscopic, thermoanalytical, and microscopic techniques have enabled the identification of the sequence of events leading to the perovskite formation and proposition of a thermolysis scheme. Retention of the molecular level mixing of the metal ions during the course of the precursor decomposition is supported by these techniques. Prior to the formation of MZrO3 (M Sr and Ca) an ionic oxycarbonate, M2 Zr2 O5 CO3 (M Sr and Ca), intermediate is produced by the thermal decomposition of the citrate precursors. I. INTRODUCTION
Mixed metal zirconate perovskites form a complete range of solid solutions with the titanate perovskites. The resultant oxides are of immense technological importance as electroceramic materials1 and calcium zirconate is used as a ceramic support in fuel cells.2 Conventional preparation of these oxides requires high temperature calcination schedules with intermittent grindings and a prolonged duration of calcination (,1200 ±C; ,48 h) for the completion of the reaction. Also, the oxides obtained by the ceramic route possess undesirable powder characteristics. A molecular precursor approach enables the synthesis of mixed metal oxides possessing desired powder characteristics. We have shown that the carboxylate precursor route is one of the convenient and the most efficient methods to produce technologically important oxides at relatively low temperatures.3–14 In the continuation of our work on citrate precursors, we report in this paper a systematic investigation on the synthesis and thermal decomposition behavior of new molecular precursors, strontium zirconyl citrate trihydrate, Sr[ZrO(C6 H6 O7 )2 ]3H2 O (SZC) and calcium zirconyl citrate monohydrate, Ca[ZrO(C6 H6 O7 )2 ]H2 O (CZC). The thermal decomposition of these molecular precursors adopts almost similar reaction pathways at the initial stages, but follows distinctly separate reaction pathways at the later stages, prior to the formation of the oxycarbonate intermediate, M2 Zr2 O5 CO3 (M Sr and a)
Presently at the Centre for Catalytic Systems and Materials Engineering, Department of Engineering, University of Warwick, Coventry CV4 7AL, United Kingdom. J. Mater. Res., Vol. 12, No. 10, Oct 1997
Ca). The present study provides chemical insight into these aspects by employing a combination of thermoanalytical and spectroscopic techniques. It is found that the zircon
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