Structure refinement, ferroelectric domains and mechanical properties of Czochralski-grown Ca9La(VO4)7 and Ca10Li(VO4)7 single crystals

Physical properties of whitlockite-type Ca3 (VO 4 ) 2 orthovanadate can be modified by incorporation of isovalent or aliovalent cation substituents. In this paper, the features of the crystal structure of Ca9La(VO4)7 and Ca10Li(VO4)7 whitlockite-type crystals grown by the Czochralski method with substitution by aliovalent La or Li ions are studied. Refinement of the structure using the Rietveld approach allowed us to determine the unit cell parameters and site occupancy. According to the data of polarization-optical studies, the formation of a strip-like ferroelectric domain structure with spontaneous polarization parallel to the third-order axis was established in the Ca9La(VO4)7 single crystal. It has been established that Ca10Li(VO4)7 is an antiferroelectric at room temperature. The correlations between Vickers hardness and fracture toughness values and the degree of crystal perfection are discussed.