Preparation and Characterization of Perovskite-type ternary Sulfides.

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Some of the ternary oxides having Perovskite-type structure, ABO_3 (A,B : metals), orrelatcd compounds exhibit interesting electuic, dielectric and/or magnetic properties, e.g., BaTiO_3, YBa_2Cu_3O_y. However, only a few termary sulfides having Perovskite-type structure have been known, so far although, several interesting possibitities, such as cathde materiasls of lithium secondary batteries can be expected for these compounds. Accordingly, I have tried to prepare Perovskite-type ternary sulfides in this study.In 1993, preparatios of LiMnS_3, LiWS_3, LiCrS_3, CuMnS_3, CuWS_3, CuCrS_3 Perovskites were carried out using each metal element, Li_2S and sulfur, in evacuated quartz tubes at temperatures of 600-800ﾟC.However, in each case excess sulfur was left in the quartz tube, and no perovskites were obtained. Accordingly, in 1994, ternary sulfides with lower sulfur compositions were prepared. In the Cu-Cr-S system, CuCr_2S_4 spinel was prepared. From this compound, some part of copper ions was rcmoved by a leaching reaction using hydrochloric acid, which could be used as a cathode material of a lithium secondary battery, and the lithium cell showed an energy density of 50 Wh/kg. In the Li-Mn-S system, a new compound, which is supposed to be the LiMn_2S_4 spinel, was obtained(no single phase was obtained). The cathode property of this material is going to be tested. In this system, Li_xMn_<1-x>S with a cubic NaCl type structure was also preparcd. The homogeniety range of this solid solution was found to be 0<x<0.27. The lattice parameter of cubic MnS decreased with increasing x value. Also, the specific resistivity of MnS(-10^<-6>OMEGA ・ cm, 20ﾟC)decreased to -10^<-2>OMEGA ・ cm for Li_<0.2>Mn_<0.8>. Li_xMn_<1-x>S is also a new compound, and characterizations are going to be carried out.