The Layered Iron Arsenide Oxides Sr2CrO3FeAs and Ba2ScO3FeAs
The iron arsenide oxides Sr2CrO3FeAs and Ba2ScO3FeAs were synthesized by high temperature solid state reactions and their crystal structures determined by the X-ray powder diffraction. Their structures are tetragonal (P4/nmm; Sr2CrO3FeAs: a = 391.12(1) pm, c = 1579.05(3) pm; Ba2ScO3FeAs: a = 412.66(5) pm, c = 1680.0(2) pm, Z = 2) and isotypic to Sr2GaO3CuS. Iron arsenide layers are sandwiched between perowskite-like metal oxide layers and separated by ~1600 pm, which is much larger compared to the ZrCuSiAs-type ‘1111' iron arsenide superconductors. The bond lengths and angles within the FeAs layers are adapted to the space requirements of the oxide blocks. Measurements of the magnetic susceptibility, electrical resistivity and temperature-dependent crystal structure show no hint for a structural phase transition or magnetic anomaly in both compounds. Sr2CrO3FeAs shows Curie-Weiss paramagnetism above 160 K with an effective magnetic moment of 3.83(3) µB in good agreement with the theoretical value of 3.87 µB for Cr3+ (S = 3/2). Antiferromagnetic ordering was detected below TN ~ 31 K. 57Fe Mossbauer spectra of Sr2CrO3FeAs show one single signal that broadens below the Neel temperature due to a small transferred hyperfine field induced by the magnetic ordering of the chromium atoms. 57Fe-Mossbauer spectra of Ba2ScO3FeAs show single signals which are only subject to weak quadrupole splitting.