High temperature structure and properties of lithium niobate

Abstract

High temperature neutron powder diffraction experiments were carried for a thorough detailed study of the structural evolution and phase transition of lithium niobate. Already at low temperatures part of the Li ions enter the hitherto assumed empty octahedra, their amount increasing with temperature. This explains anomalies in the thermal expansion. The phase transition from the ferroelectric to the paraelectric phase proceeds in two steps, complete disordering of Li before Nb reaches its centrosymmetric site within its octahedron. Li is further disordered within the oxygen plane pointing towards relatively strong Li-O bonds. These results settle a number of controversies found in the literature and add new aspects.