Euhedral crystals of Na2TiGeO5 with switchable translucency and reorientable microstructure

Abstract

When external stimuli are applied on a ferroic material, an ordered microstructure with crystallographic deformations (twins) is formed within the initially homogeneous crystal. However, when the crystal twins are formed during the crystallization, their integrated effect on the crystal properties is poorly examined. This work reveals a mild hydrothermal synthesis of euhedral ferroelastic crystals of sodium germanium titanate (Na₂TiGeO₅) with ordered twin patterns that can be selectively manipulated with an adaptive beam of light. Within the idiomorphic crystals, a regular circuit of translucency adjustable sectors detached by the combination of permanent and switchable interfaces embedded in equivalent facets is found. The crystals also reveal a rare combination of chemically equivalent segments with contrasting refractive indexes. Finally, by simple fracturing of the crystals, a microstructural reorientation under ambient conditions is achieved.