Structural phase transitions in KNbO 3 and Na 0.5 K 0.5 NbO 3

摘要: The in-situ high-temperature single-crystal X-ray diffraction experiments on KNbO3 (KN) and Na0.5K0.5NbO3 (NKN) revealed a series of structural evolution associated with two transitions among orthorhombic, tetragonal cubic forms. Upon heating, the pseudocubic unit cell volume collapsed discontinuously at these transition points, whereas reverse took place upon cooling, indicating that both were first-order. coordination numbers Nb showed decreasing tendency temperature, i.e., 6 in cubic, 5+1 tetragonal, 4+2 orthorhombic. difference ionic size between Na K gave atom an attribute rattling cavity surrounded by corner-sharing NbO6 octahedra NKN. small not only vibrated large amplitude, but also shifted further from centre than K. number was always compared all temperatures, 8+4 7+5 phase KN occurred similar way as NKN, though temperatures slightly toward high temperature side.