Synthesis, structural and spectral characteristics of Cd3O2SO4

Abstract

X-ray diffraction and thermogravimetric analysis methods were used to reveal conditions for the formation and thermal stability of cadmium oxosulfate Cd3O2SO4 synthesized by heating β-Cd2(OH)2SO4 in air. The crystal structure of Cd3O2SO4 was studied for the first time. It was shown that it is built by alternation of two types of blocks oriented parallel to the bc plane. The first type block consists of CdO8 clusters connected with each other by SO4 tetrahedra. The space between these blocks is occupied by blocks composed of tetragonal CdO5 pyramids connected with neighboring CdO8 blocks. The connections are carried out both through bridging oxygen atoms and oxygen atoms belonging to SO4 clusters. The unit cell parameters of Cd3O2SO4 are a=12.1762 (1) Å, b=6.85421 (5) Å, c=6.97322 (6) Å, β=106.5578 (6)°, V=557.840 (8) Å3, Z=4, sp. gr. C2/c. Vibrational spectroscopy data are in complete agreement with the crystal structure analysis. The UV-Vis-NIR spectra demonstrate the semiconducting nature of Cd3O2SO4 with the band gap of 3.45 eV stable at different heating temperatures. The energy band structure of Cd3O2SO4 has been studied by means of the first-principle pseudo-potential PAW method, VASP software package. The calculations performed point to a high probability of oxygen vacancies formation under the indicated synthesis conditions. However, the presence of vacancies does not lead to the appearance of vacancy bands inside the band gap, i.e., in accordance with experiment, they do not significantly affect the optical properties of Cd3O2SO4.