High-pressure stabilisation of R = Y member of R2CuTiO6 double perovskite series

Double perovskite oxides of the A2B’B″O6 type with Jahn-Teller active Cu2+ as the B′ constituent have gained considerable research interest in recent years. For fundamental studies, the rare earth element (R) based systems such as R2CuTiO6 form an intriguing research platform as they allow systematic chemical-pressure studies by simply controlling the size of the R constituent. However, for the R2CuTiO6 compounds conventional ambient-pressure high-temperature synthesis yields an orthorhombic (Pnma) double perovskite structure for the largest R constituents (La–Gd) only, while the compounds with the smaller R:s adopt a hexagonal structure. Here we demonstrate a hexagonal-to-perovskite structure conversion for the R ​= ​Y compound achieved through a high-pressure (HP) high-temperature treatment at 4 ​GPa and 1000 ​°C. Structural details of the thus stabilized new double perovskite phase of Y2CuTiO6 are addressed through a combined DFT simulation and Rietveld refinement study, revealing signs towards the rare layered-type ordering of the B-site (Cu and Ti) cations. Similar to the previously reported R2CuTiO6 perovskite phases with R ​= ​La, Pr, and Nd, the R ​= ​Y member is found paramagnetic throughout the measured temperature range of 5–300 ​K. From UV–vis absorption measurements the optical bandgap is estimated to be ca 3.4 ​eV.