STRUCTURE OF THE PEROVSKITES ALONG THE SrTiO₃-SrGeO₃ JOIN. Andrzej Grzechnik, Herve Hubert, William Petuskey, and Paul McMillan, Arizona State University, Materials Research Group in High-Pressure Synthesis, Department of Chemistry and Biochemistry, Box 871604, Tempe, AZ 85287-1604

In this study, we report a new, high-pressure synthesis route to obtain mixed compounds along the perovskite join with non-transition (metastable phase) and transition metal B cations in the cubic ABO₃ structure. SrGeO₃ perovskite is stable above 6 GPa and 1273 K. When it is externally heated to 673 K, it completely decomposes into a mixture of amorphous and lowpressure phases. The onset of decomposition is observed as low as 398 K. The large temperature range (about 300 K) where decaying metastable SrGeO₃ perovskite coexists with other phases suggests that the decomposition occurs locally in nucleation sites with different stress fields. The SrGeO₃-SrTiO₃ phases were synthesized from mixtures of SrTiO₃ and SrGeO₃ (an ambient pressure pseudowollastonite polymorph) at 7 GPa and 1373 K with a multiple anvil high-pressure and high-temperature device. Recovered material was analyzed with X-ray diffraction. The analysis of the X-ray patterns reveals that all the synthesized compounds are disordered with the Pm3m space group, indicating that there is a complete SrGeO₃-SrTiO₃ solid solution at the synthesis conditions. Future analysis of the Raman spectra will allow examination of possible ordering on the nanometer scale and the degree of metastability of the obtained phases.