NaTePO5, SrTeP2O8 and Ba2TeP2O9: Three tellurite-phosphates with large birefringence

Two new tellurite-phosphates NaTePO5, SrTeP2O8 and the previously reported Ba2TeP(2)O(9) were synthesized successfully via high-temperature solid-state reactions and their structures were determined by single-crystal X-ray diffraction. The structures of NaTePO5 and SrTeP2O8 feature two-dimensional (2D) [TePO5](-) and [TeP2O8](2-) anionic layers interleaved with Na+ and Sr2+ cations, respectively. The P-31 NMR spectra show that electron density around phosphorus atoms in SrTeP2O8 is slightly larger than that in Ba2TeP(2)O(9), owing to the connection modes of [TeO5] and [PO4] units and counter-ion effects. The calculated electric field strength (Z/a(2)) based on the P-31 chemical shift indicate as the chemical shift increases the Z/a(2) also increases, as evidenced by the binding energy of P 2p determined by the X-ray photoelectron spectroscopy. Further, first-principle calculations show that the NaTePO5, SrTeP2O8 and Ba2TeP(2)O(9) exhibit large birefringence of 0.212, 0.133 and 0.126 at 1064 nm, respectively, compared to other phosphates. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Two new tellurite-phosphates NaTePO5, SrTeP2O8, and the previously reported Ba2TeP(2)O(9) were successfully synthesized via high-temperature solid-state reactions and their structures were determined by single-crystal X-ray diffraction. The P-31 NMR spectra showed slightly larger electron density around phosphorus atoms in SrTeP2O8 compared to Ba2TeP(2)O(9), due to different connection modes of [TeO5] and [PO4] units. Calculated electric field strengths and birefringence values of NaTePO5, SrTeP2O8, and Ba2TeP(2)O(9) indicate differences in their properties compared to other phosphates.