Phase relationships of the lithium halide spinels Li 2MCl 4-Li 2MBr 4 with M = Mn, Fe, Cd

Abstract

The sections Li 2 MCl 4−4xBr 4x of the quaternary systems LiCl-LiBr- MCl 2- MBr 2 with M = Mn, Cd, and Fe were studied by high-temperature X-ray diffraction patterns and DTA and DSC measurements. In the quasibinary lithium manganese halide system complete series of solid solutions exist between the inverse spinels Li 2MnCl 4 and Li 2MnBr 4. Li 2MnBr 4 and solid solutions with x > 0.54 undergo phase transitions to tetragonal spinels at lower temperatures. In the nonquasibinary system with M = Cd, only at temperatures near 400°C a complete series of mixed crystals is formed. At lower temperatures the system is mainly two-phase with rock salt-type Li 1− y Cd 0.5 y Cl 1− x Br x and cadmium chloride-type Cd 1− y Li 2 y Cl 2−2 x Br 2 x solid solutions in equilibrium. The lithium iron halide system is similar to that of cadmium, but spinel-type Li 2FeBr 4 does not exist at any temperature. The manganese and cadmium halide spinels and spinel solid solutions undergo phase transitions to NaCl defect structures at elevated temperatures.