Salt-flux synthesis of complex oxides: Cs_0.33MoO₃, CsFe(MoO₄)₂, and the inverse salt-inclusion phase Cs₂Mo_0.65O_0.21Cl_5.44

Abstract

Recent work on the growth of complex oxides in salt fluxes is reviewed. Single crystals of Cs_0.33MoO₃, CsFe(MoO₄)₂ and the new phase, Cs₂Mo_0.65O_0.21Cl_5.44, have been grown from the reaction of metal oxides Fe₂O₃, MoO₃ and molybdenum powder in a eutectic CsCl/NaCl flux. Cs_0.33MoO₃ is one of the known molybdenum bronzes, featuring mixed valent molybdenum ions. CsFe(MoO₄)₂ has a layered KAl(MoO₄)₂ structure, which consists of infinite slabs of corner-sharing MoO₄ and FeO₆ polyhedra separated by layers of Cs⁺ cations. Cs₂Mo_0.65O_0.21Cl_5.44 forms with a new structure type (orthorhombic, Cmcm, a = 7.434(1) Å, b = 17.330(3) Å, c = 8.074(1) Å, Z = 4) which is comprised of isolated [Mo(O/Cl)Cl₅] octahedra embedded in a distorted CsCl matrix. Magnetic susceptibility measurements indicate antiferromagnetic ordering for both CsFe(MoO₄)₂ (T _N = 4.5 K) and Cs₂Mo_0.65O_0.21Cl_5.44 (T _N = 7 K).

Keywords:

• inverse salt-inclusion solids
• molten salt synthesis
• halide flux method
• reduced molybdate

Acknowledgements

We thank Dr. Bert van der Burgt for his assistance with the Raman spectroscopy. This work made use of the SEM facilities of the Physics Department at FSU. This research was supported by the Florida State University (FSU) Department of Chemistry and Biochemistry and by the National Science Foundation (grant number DMR-05-47791).