Apatite-Like Complex Oxides in the Ca-Cr-Cu-O System: Synthesis, Crystal Structure, XPS and Magnetic Study

Calcium chromates Ca5(CrO4)3Cux(OH)1–x with apatite structure and different content of copper and OH– groups have been synthesized by solid‐phase reactions under usual conditions in air. The composition, structure, degree of oxidation of the elements, and the properties of the produced chromates have been characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy (XPS), differential thermal analysis (DTA), thermogravimetric analysis (TGA), and magnetochemical methods. It was concluded that the reason for the apatite stabilization is the introduction of Cu+ and Cu2+ cations into the hexagonal O(4) sites in the tunnels of the Ca5(CrO4)3OH apatite structure. This is caused by the substitution of OH– according to the scheme OH– → (Cu+O)– or 2 OH– → (Cu2+O2)2– which gives rise to infinite chains along the c‐axis. Ca5(CrO4)3Cux(OH)1–x (0 ≤ x ≤ 0.84) with apatite structure were synthesized by solid‐phase reactions under usual conditions. According to X‐ray photoelectron spectroscopy (XPS) and magnetic measurements, the valence state of Cr is +5 and that of Cu presumably +2 and +1.