In situ investigation of the microstructure of KGd(WO4)2 crystal growth boundary layer by confocal laser Raman microscopy

Abstract

The microstructure of the solution near the crystal–solution interface is important for understanding the crystal growth mechanism. The microstructure of KGd(WO₄)₂ crystal growth boundary layer was studied in situ by confocal laser Raman microscopy. The experimental results show that a free WO₄ tetrahedron is the basic structural unit in KGd(WO₄)₂–K₂W₂O₇ high temperature solution, and distorted WO₆ octahedron, WOW and WOOW oxygen bridge bonds begin to appear and increase in concentration with the positions moving towards the crystal–solution interface. Meanwhile, a quasi-ordered boundary layer with the thickness of 50–70 μm was found near the interface. A growth mechanism of structural evolution was proposed in the boundary layer, where free WO₄ tetrahedra are transformed into distorted WO₆ octahedral long chain structures by forming the WOW and WOOW oxygen bridge bonds. According to the growth mechanism, the KGd(WO₄)₂ crystal growth behaviour can be understood very well.