Novel laser crystals in Ca9Y(VO4)(7-x)(PO4)(x) mixed system

摘要

The Ca9Y(VO4)(7-x)(PO4)(x) (x = 0, 1, 3, 4) solid solution whitlockite-like single crystals have been grown by the Czochralski method from mixtures of single phase Ca9Y(VO4)(7) and Ca9Y(PO4)(7) starting materials produced by solid-state synthesis. Real compositions of solid solution crystals has been determined and analyzed. It is found that crystals with x = 0, 1, 4 exist with polar structure at room temperature, space group R3c. At least one of them, Ca9Y(VO4)(7), demonstrates ferroelectric behaviour with phase transition at 942 degrees C. Unlike the others, Ca9Y(VO4)(3)(PO4)(4) crystallizes in centrosymmetric whitlockite-like structure with space group R3c confirmed by single-crystal X-ray structure analysis. Similar to other whitlockite-family phosphates and vanadates, its crystal structure is described as a disordered structural version of usual whitlockites, corresponding to their high-temperature paraelectric phases. The transmission and luminescence spectra of solid solution crystals are reported, the hardness H-v and fracture toughness K-1c of solid solution single crystals are also determined. (C) 2017 Elsevier B.V. All rights reserved.