PREDICTIVE MODELING AND HIGH-PRESSURE - HIGH-TEMPERATURE SYNTHESIS OFPEROVSKITES CONTAINING MONOVALENT SILVER

The program POTATO, which was developed to model distorted perovskite structures, has been used to assess the stability of hypothetical comp ositions and guide the synthesis of new materials at high pressures an d high temperatures. The initial result of this effort is the synthesi s of two new perovskites, Ca2NdAgTi4O12 and NdAgTi2O6, which were synt hesized at 14-14.5 GPa and 1000 degrees C using the uniaxial split sph ere anvil type press (USSA-2000). Both compounds are perovskites disto rted from the ideal cubic structure by octahedral tilting distortions. Ca2NdAgTi4O12 contains a random distribution of Ca2+/Nd3+/Ag+ ions on the A-site, whereas NdAgTi2O6 has a partially ordered distribution of Nd3+/Ag+ ions. Ca2NdAgTi4O12 adopts the GdFeO3 structure (Glazer tilt system b(-)a(+)b(-)), space group Pnma, with a = 5.44883(4), b = 7.68 915(6), and c = 5.42290(3) Angstrom. NdAgTi2O6 belongs to the tetragon al space group P4/nbm, with a 5.45337(3) and c = 7.72934(6) Angstrom. This structure can be derived from the simple cubic perovskite structu re by rotations of the octahedra about the c-axis (Glazer tilt system a(0)a(0)c(-)) and partial ordering of Nd3+ and Ag+ ions into alternati ng layers, perpendicular to the c-axis.