Synthesis, crystal structure of Ca6Sb2O11 from experiments and DFT-electron structure calculation

This article reports a new perovskite compound Ca6Sb2O11. The X-ray powder diffraction technique was used to analyze its crystal structure. The results show that Ca6Sb2O11 has a tetragonal structure with the I4/m space group, and the lattice parameters are a = b = 5.658 (1) & Aring;, c = 7.984 (1) & Aring;, alpha = beta = gamma = 90 degrees. It exhibits a typical A4B'2B '' 2X12-x anoxic multi-perovskite structure with rock-salt ordering of the B-site cations. The compound's chemical composition and valence states were characterized through scanning electron microscopy-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies was confirmed by electron paramagnetic resonance (EPR) spectroscopy. A chemical and structure transition temperature and the full melting temperature of Ca6Sb2O11 were measured, with values of 1515 +/- 3 K and 1720 +/- 3 K, respectively. The density functional theory (DFT)-electron structure calculation results show that Ca6Sb2O11 is an indirect wide-band gap (-4.47 eV) semiconductor material, which agrees well with the experimental value (-4.38 eV) obtained through diffuse reflection spectroscopy (DRS). Moreover, the top of the valence band and bottom of the conduction band are mainly contributed to by O-2p and Ca-3d states, respectively.