Crystal Structures and Magnetic Properties of CrO4-4-Containing Oxides: Sr2CrO4, Ba2CrO4, and Ba3CrO5

Refinement of the crystal structures of Ba2CrO4 and Ba3CrO5 using powder neutron diffraction data has confirmed that the former is isostructural with β-K2SO4 and the latter isostructural with Cs3CoCl5. Ba2CrO4 is orthorhombic, Pnma (No. 62), Z = 4 with a = 7.6285(5) Å, b = 5.9136(5), c = 10.4639(8), and V = 472.04(5) Å3 Ba3CrO5 is tetragonal, I 4/mcm (No. 140), Z = 4 with a = 7.3033(3) Å, c = 11.6704(6), V = 622.48(4) Å3 from powder Guinier X-ray diffraction data. Magnetic properties of Sr2CrO4, Ba2CrO4, and Ba3CrO5 were examined down to 2-5 K. The structures and magnetic properties of Sr2CrO4 and Ba2CrO4 are compared with their vanadium analogues β-Sr2VO4 and β-Ba2VO4. Unlike isostructural β-Sr2VO4 which contains the V2O8-8 dimer, Sr2CrO4 contains truly isolated CrO44 tetrahedra and its magnetic behavior can be best described as a dimerized chain. Ba2CrO4 and Ba3CrO5 also contain isolated CrO4-4 tetrahedra. Ba2CrO4 is paramagnetic down to 5 K. Ba3CrO5 undergoes long-range magnetic order at ∼8 K, a temperature range significantly higher than that of isostructural Rb3CoCl5 and Cs3CoX5(X = Cl, Br).