Phase Transition and Internal Crystal Structure of Superprotonic Conductor, Rb_3−xK_xH(SeO₄)₂

Abstract

Solid solutions of superprotonic conductors, Rb 3-x K x H(SeO 4) 2 , were studied by means of conductivity measurements and single crystal neutron structure analyses. The conductivity measurements demonstrated that the phase transition temperature to the superprotonic phase decreased as x increased and the change of the phase transition temperature was non-linear to x. The single crystal neutron diffraction experiments revealed that the sample with x = 2 formed a superstructure with the modulation vector of (1/2 1/2 1/2). The structure analyses with the original cell showed that K ions preferred to occupy one of two possible sites and the distortion of the SeO 4 tetrahedron have close correlation with the phase transition temperature.