Phase Instability, Oxygen Desorption and Related Properties in Cu-Based Perovskites Modified by Highly Charged Cations

The rock-salt ordered A2CuWO6 (A = Sr, Ba) with I4/m space group and disordered SrCu0.5M0.5O3−δ (M = Ta, Nb) with Pm3m space group perovskites were successfully obtained via a solid-state reaction route. Heat treatment of Ba2CuWO6 over 900 °C in air leads to phase decomposition to the barium tungstate and copper oxide. Thermogravimetric measurements reveal the strong stoichiometric oxygen content and specific oxygen capacity (ΔWo) exceeding 2.5% for Ba2CuWO6. At the same time, oxygen content reveals Cu3+ content in SrCu0.5Ta0.5O3−δ. Under the following reoxidation of Ba2CuWO6, step-like behavior in weight changes was observed, corresponding to possible Cu+ ion formation at 900 °C; in contrast, no similar effect was detected for M5+ cations. The yellow color of Ba2CuWO6 enables to measure the band gap 2.59 eV. SrCu0.5Ta0.5O3−δ due to high oxygen valance concentration has a low thermal conductivity 1.28 W·m−1·K−1 in the temperature range 25–400 °C.