Ba/Zr=1:1 freeze-dried and conventional chloride powders:: synthesis of BaZrO3 and phase formation

Precursor powders of Ba/Zr = 1:1 chloride have been prepared by freeze drying (FD) and conventional mixing. A simple, laboratory-made apparatus for sublimation of the frozen water from the cryo-particles is presented. Both powders have the same phase formation behavior. Up to 500-600 degreesC, Zr chloride transforms into ZrO2. At high temperatures, BaCl2 starts melting and decomposing and two subsequent processes take place: (a) chlorination of the Zr atoms from the oxide and (b) formation of BaZrO3 phase, These processes depend on treatment atmosphere and reactivity of the starting powders. Freeze-dried powders with higher reactivity and/or O-2 atmosphere are suitable to obtain high content of BaZrO3 phase. In the freeze-dried powder, decomposed in O-2 atmosphere at 1190 degreesC for 20 h, 90% of BaZrO3 phase content was attained. No new phases were observed during decomposition of the freeze-dried powder. In the as-synthesized freeze-dried powder, some XRD lines remained unidentified. (C) 2003 Elsevier B.V. All rights reserved.