ИСТИНА

The recent discovery of high-temperature superconductivity in La(O,F)FeAs [1] has triggered a burst of interest in search of new compounds bearing [Fe2As2] and other anti-fluorite layers. Most of this work has been done by analogy with the oxychalcogenides, a family that is structurally and chemically related to the target pnictides. A cursory survey of the oxyhalide family shows that whereas Ca2+ is a typical constituent of perovskite blocks therein, this cation had not yet been used to contribute to the chalcogenides and pnictides. As both Fe3+ and Cu2+ are redox-incompatible with the pnictide anions, the search for new calcium-bearing compounds has been conducted among oxychalcogenides. We have synthesized two new perovskite oxychalcogenides, Ca2CuFeO3S and Ca2CuFeO3Se, in sealed quartz tubes. They crystallize in Sr2CuGaO3S-type structure (SG - P4/nmm) with lattice parameters a=3.8271(1), c=14.9485(2) Å and a=3.8605(1), c=15.3030(2) Å for Ca2CuFeO3S and Ca2CuFeO3Se, respectively. They appear to be the first layered chalcogenide perovskites involving calcium and are structural analogs of the corresponding Sr and Ba compounds [2]. The new compounds exhibit semiconducting properties with energy gap decreasing from the oxysulfide to the oxyselenide. References 1. Y. Kamihara et al, J. Am. Chem. Soc. 130, 3296 (2008). 2. W. J. Zhu and P.H. Hor, J. Solid State Chem. 134, 128 (1997).