Crystal Structure of High Temperature Phase and Ionic Conductivity Mechanism of CuHgSX (X = Cl, Br)

We found a new ionic conduction phase in CuHgSCl above 373 K and in CuHgSBr above 346 K. The crystal structures of these novel phases have been determined by Rietveld refinement of powder X-ray diffraction patterns. The electric conductivity at 500 K measured by AC impedance method was 1.4 × 10^-5 S cm^-1 for CuHgSCl and 4.0 × 10^-6 S cm^-1 for CuHgSBr. The activation enthalpy was determined to be 53 kJ mol^-1 for CuHgSCl and 67 kJ mol^-1 for CuHgSBr. The ionic transport number measurements indicated that Cu^+ ions constitute the majority charge carriers in these samples. The electronic contribution to the conduction process is small in comparison with the Cu^+ ionic contribution. The charge density analysis by the maximum entropy method (MEM) combined with Rietveld analysis clearly showed that the Cu^+ ionic conduction path was along the crystallographic (100) direction.