Self-powdering and nonlinear optical domain structures in ferroelastic β′-Gd2(MoO4)3 crystals formed in glass

Ferroelastic β′-Gd2(MoO4)3, (GMO), crystals are formed through the crystallization of 21.25Gd2O3–63.75MoO3–15B2O3 glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50–500 μm spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called “self-powdering phenomenon during crystallization” in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and a spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO4)2− tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals.