Study of materials structure physics of isomorphic LiNbO_3 and LiTaO_3 ferroelectrics by synchrotron radiation X-ray diffraction

摘要

Electron charge density studies of stoichiometric LiNbO3 and LiTaO3 ferroelectrics have been carried out by analyzing the synchrotron radiation X-ray powder diffraction data using a combination of the Rietveld and maximum entropy methods. The clear relationships between the Nb(Ta)-O bond length, the electron charge density on the Nb(Ta)-O bond, and the phase transition temperature T-C are revealed for isomorphic structures. Nb(Ta)-O bonding plays an important role in the elevation of T-C. The T-C in LiNbO3 being higher than that in LiTaO3 is attributed to the larger lattice distortion of the Nb-O oxygen octahedron in LiNbO3. The validity of estimating T-C for LiNbO3 family crystals from the degree of lattice distortion in the ferroelectric structure is discussed. (C) 2018 The Japan Society of Applied Physics