CoTeO₄ - a wide-bandgap material adopting the dirutile structure type

High-quality crystals of CoTeO4 were grown by application of chemical vapor transport reactions in closed silica ampoules, starting from polycrystalline material in a temperature gradient 640 degrees C -> 580 degrees C with TeCl4 as transport agent. Crystal structure analysis of CoTeO4 from single crystal X-ray data revealed a dirutile-type structure with Co-II and Te-VI atoms at crystallographically distinct sites, each with point group symmetry . The statistical significance and accuracy of the previously reported structural model based on powder data with the ordered arrangement of Co and Te cations was noticeably improved. CoTeO4 does not undergo a structural phase transition upon heating, but decomposes stepwise (Co2Te3O8 as intermediate phase) to Co3TeO6 as the only crystalline phase stable above 770 degrees C. Temperature-dependent magnetic susceptibility and dielectric measurements suggest antiferromagnetic ordering at similar to 50 K. Optical absorption spectroscopy and computational studies reveal wide-band semiconductive behavior for CoTeO4. The experimentally determined band gap of similar to 2.42 eV is also found for CdS, which is frequently used in photovoltaic systems but is hazardous to the environment. Hence, CoTeO4 might be a possible candidate to replace CdS in this regard.