Predictive Modeling and High-Pressure−High-Temperature Synthesis of Perovskites Containing Monovalent Silver

The program POTATO, which was developed to model distorted perovskite structures, has been used to assess the stability of hypothetical compositions and guide the synthesis of new materials at high pressures and high temperatures. The initial result of this effort is the synthesis of two new perovskites, Ca 2 NdAgTi 4 O 12 and NdAgTi 2 O 6, which were synthesized at 14−14.5 GPa and 1000 °C using the uniaxial split sphere anvil type press (USSA-2000). Both compounds are perovskites distorted from the ideal cubic structure by octahedral tilting distortions. Ca 2 NdAgTi 4 O 12 contains a random distribution of Ca 2+ /Nd 3+ /Ag + ions on the A-site, whereas NdAgTi 2 O 6 has a partially ordered distribution of Nd 3+ /Ag + ions. Ca 2 NdAgTi 4 O 12 adopts the GdFeO 3 structure (Glazer tilt system b - a + b - ), space group Pnma, with a = 5.44883(4), b = 7.68915(6), and c = 5.42290(3) Å. NdAgTi 2 O 6 belongs to the tetragonal space group P 4 /nbm, with a = 5.45337(3) and c = 7.72934(6) Å. This structure can be derived from the simple cubic perovskite structure by rotations of the octahedra about the c -axis (Glazer tilt system a 0 a 0 c - ) and partial ordering of Nd 3+ and Ag + ions into alternating layers, perpendicular to the c -axis.