Structural analyses of a K2O-rich KNbO3 melt and the mechanism of KNbO3 crystal growthElectronic supplementary information (ESI) available: Calculated optical modes of the orthorhombic KNbO3 crystal and their frequencies, calculated Raman spectrum of the tetragonal KNbO3 crystal, group theory analyses for the vibrational modes of the tetragonal and cubic KNbO3 crystal, optimized structure of the K[NbO2Ø2] and K[NbO3] groups and their calculated optical modes and frequencies. See DOI: 10.1039/c4c

• Main Authors: Wan, Songming, Zhang, Bo, Sun, Yulong, Tang, Xiaolu, You, Jinglin
• Format: Journal Article
• Language: English
• Published: 18.03.2015
• ISSN: 1466-8033
• DOI: 10.1039/c4ce01992j

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 K 2 O-rich KNbO 3 (KN) melt which was in equilibrium with a KN crystal. K + ions and isolated NbO 3 − groups have been found to be the main structural units in the bulk melt. The NbO 3 − units connect with each other near the crystal-melt interface to form NbO 2 Ø 2 − (Ø = bridging oxygen) chains that further form NbØ 6 − 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. A mechanism was proposed to describe KNbO 3 crystal growth from a K 2 O-rich KNbO 3 melt on the basis of in situ Raman spectroscopy experiments and density functional theory analyses.