Ionic conductivity and structure of halocomplex salts of group 13 elements

Ionic conductivities of the complex salts between monohalides of Li, Cu, and Ag and trihalides of Al, Ga, and In were studied by means of NMR, NQR, powder X-ray diffraction, DTA, and AC conductivity measurements. The cation diffusion in the halocomplex was confirmed by measuring the temperature dependence of the NMR linewidth. The activation energies of the cation diffusion were 36, 52, 51, and 44 kJ mol−1 for LiGaBr4, CuAlCl4, CuAlBr4, and CuGaBr4, respectively. The ionic conductivities of the Ag salts, AgMBr4 (M=Al, Ga) were one order of magnitude higher than those of the corresponding Cu salts, CuMBr4 (M=Al, Ga). This finding may be due to the difference in crystal structure. The ionic conductivities of RGaBr4 (R=Li, Cu, and Ag) were higher than those of the corresponding Al salts, RAlBr4 at room temperature, suggesting that the ionic conductivity is mainly governed by the ratios of the cationic radius to the anionic one. The high-temperature phase of Li3InBr6 is a Li+ superionic conductor. When CaBr2 was doped into Li3InBr6, the ionic conductivity varied with the amounts of CaBr2. From the substitution effect of the cation, it is considered that the high ionic conductivity results from the considerably disordered state of the cationic sublattice.