K₂TeP₂O₈: a new telluro-phosphate with a pentagonal Te-P-O layer structure

A new telluro-phosphate K2TeP2O8 was synthesized by a high temperature solution method. It crystallizes in the orthorhombic space group P21212 and features a [TeP2O8]2- layer structure, which is the first layer structure built by Te-O and P-O groups among the telluro-phosphates. More interestingly, the layer structure in K2TeP2O8 is nearly pentagonal. First-principles theoretical calculations suggest that K2TeP2O8 possesses a large birefringence compared to phosphates. Furthermore, IR spectra, UV-vis-NIR diffuse reflectance spectroscopy data, thermal behavior, and electronic structure calculations were studied.