An investigation of the structural dynamics in the fast ionic conductor Cu2−δSe using neutron scattering

Energy resolved neutron diffraction measurements were performed on Cu1.75Se and Cu1.98Se samples for both α- and β-phases. In-situ measurements of the Cu1.98Se compound during heating show that the β–α phase transition takes place at 420 K and has noticeable temperature hysteresis. In addition to Bragg reflections, the diffraction patterns of the α-Cu1.75Se at RT and α-Cu1.98Se at 435 K samples taken in conventional two-axis geometry show a broad maximum related to diffuse scattering. This diffuse background is suppressed in the energy resolved experiment which indicates a strong contribution from inelastic scattering coming from correlated thermal displacements of the ions in the super-ionic phase. On the other hand, the diffraction pattern of the non super-ionic β-phase shows only minor differences between spectra measured with and without the analyser crystal.