Synthesis, Structure, and Physical Properties of RbCr₂Se₂O

Layered compounds containing the T₂O plane (T = transition metal), which is the anti-type of the CuO₂ plane in cuprate superconductors, have been explored widely because of their diverse physical properties. Among them, KV₂Se₂O has attracted much attention due to its interesting physical properties, especially the magnetic order. In this work, we report a new isostructural chromium oxyselenide, RbCr₂Se₂O. It was synthesized using a solid-state method using Rb₂CO₃ as the source of Rb and O for the title compound, with the assistance of Ba. The compound crystallizes in the space group P4/mmm with lattice parameters a = 4.01123(8) Å and c = 7.49357(18) Å. Magnetic susceptibility measurements indicate an antiferromagnetic transition at 345 K for RbCr₂Se₂O and also above room temperature, as the Néel temperature is T_N ≈ 400 K for KV₂Se₂O. The analysis of variable temperature XRD data reveals the anisotropic thermal expansion of the RbCr₂Se₂O lattice. The almost unchanged lattice parameter a near the transition temperature and the broad peak with an onset temperature of ~360 K in the differential scanning calorimetry data may have a relationship with the magnetic ordering. The measurement of electrical resistivity demonstrates the semiconducting behavior of RbCr₂Se₂O. The thermal activation model and variable-range hopping model are proposed to describe the conduction mechanism in the high- and low-temperature ranges, respectively.