Local structure and phase transitions of KNbO3

Abstract

Bond length distributions of nearest- and higher-neighbor distances in KNbO3, which is the parent compound of lead-free piezoelectric materials, have been obtained by X-ray pair-distribution function (PDF) analysis. The Rietveld analysis of high-energy powder X-ray diffraction data as a function of temperature from 15 to 1073 K over four phases shows the variation in structure from rhombohedral to cubic structures. The refinements on the local structure by the PDF method indicate that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion is maintained locally in all four phases.