Hydrothermal Crystal Growth of Mixed Valence Cs2SbBr6

Mixed valence perovskite materials present an opportunity to understand how structural motifs influence electronic properties in semiconducting materials. Here, we report the preparation of high-quality single crystals of the mixed valence compound Cs2SbBr6, which can also be written as (Cs4SbSbBr12)-Sb-III-Br-V. We have determined the solubility of Cs2SbBr6 under myriad reaction conditions which permits the prescription of conditions to grow large, high-quality single crystals. Single-crystal X-ray diffraction confirms the crystal structure of this material and shows that the crystal structure is preserved from T = 100 to 380 K, and the heat capacity measurements show an absence of any anomalies due to phase transitions between T = 2 to 150 K. Furthermore, we illustrate that the mixed valence of the Sb centers in this material charge order into interpenetrating diamond lattices. We also show that the habit of Cs2SbBr6 single crystals is defined by well-formed faces along the close-packed planes of bromine atoms.