SPINEL-TYPE TERNARY SULFIDES FECR2S4 AND MNCR2S4

In their stability domains (medium or high sulfur pressures) between 6 00 and 1000 degrees C, FeCr2S4 and MnCr2S4 are weak p type non-stoichi ometric semiconductors. Their conductivity ranges are 2.3<log sigma(Fe Cr2S4) (Omega m)(-1) <3.3 and 0.5 < log sigma (MnCr2S4) (Omega m)(-1) < 2.0; with small variations as a function of P-s2 explicable by catio nic disorders. The non-stoichiometries, narrow for MnCr2S4 and large f or FeCr2S4 are due to metallic vacancies. So the p-type spinels can be written (FeCr2)(1-phi)S-4 and (MnCr2)(1-zeta)S-4 with 0<psi<0.03 and 0<zeta<0.002. The appearance of interstitial chromium (n type) in the lower P-S2 provokes the decomposition of spinels. (C) 1998 Elsevier Sc ience S.A.