Structural analyses of a K2O-rich KNbO3 melt and the mechanism of KNbO3 crystal growth

A melt structure is an intrinsic factor used to govern a variety of melt macro-properties and plays a fundamental role in understanding crystal growth mechanisms. In this paper, high-temperature Raman spectroscopy and a density functional theory (DFT) method were used to investigate the structure of a K2O-rich KNbO3 (KN) melt which was in equilibrium with a KN crystal. K+ ions and isolated NbO3− groups have been found to be the main structural units in the bulk melt. The NbO3− units connect with each other near the crystal–melt interface to form NbO2O2− (O = bridging oxygen) chains that further form NbO6− octahedra (the basic units in the KN crystal structure) on the crystal–melt interface. A boundary layer with the thickness of about 5 μm was observed around the interface. The DFT calculations verified the melt structures and provided accurate assignments for the vibrational bands present in the melt Raman spectra.