REECOB: 20 Years of Rare Earth Element Calcium Oxoborates Crystal Growth Research

Rare earth element calcium oxoborates (REECOB, REECa₄O[BO₃]₃) represent a group of materials for non-linear optics and with useful piezoelectric properties under high-pressure and high-temperature conditions making it applicable as sensor materials in extreme environments. High-quality crystals with appropriate size are generally grown from a melt by the Czochralski method. This article presents a compilation and comparison of crystal growth parameters and properties of members of the REECOB group from the literature with those of own growth experiments. Recent studies provided new data concerning the melting temperature of REECOB members, such as ca. 1475°C for SmCa₄O(BO₃)₃ (SmCOB). In addition, first data on the change of thermal expansion coefficients of SmCOB are presented and discussed.