Supercritical hydrothermal synthesis of Cu2O(SeO3): Structural characterization, thermal, spectroscopic and magnetic studies

Cu2O(SeO3) has been synthesized in supercritical hydrothermal conditions, using an externally heated steel reactor with coupled hydraulic pump for the application of high pressure. The compound crystallizes in the P213 cubic space group. The unit cell parameter is a = 9.930(1) Å with Z = 12. The crystal structure has been refined by the Rietveld method. The limit of thermal stability is, approximately, 490 °C. Above this temperature the compound decomposes to SeO2(g) and CuO(s). The IR spectrum shows the characteristic bands of the (SeO3)2− oxoanion. In the diffuse reflectance spectrum two intense absorptions characteristic of the Cu(II) cations in five-coordination are observed. The ESR spectra are isotropic from room temperature to 5 K, with g = 2.11(2). The thermal evolution of the intensity and line width of the signals suggest a ferromagnetic transition in the 50–45 K range. Magnetic measurements, at low temperatures, confirm the existence of a ferromagnetic transition with a critical temperature of 55 K.