First Principle Assisted Prediction of the Birefringence Values of Functional Inorganic Borate Materials

Abstract

Prediction of the birefringence values of borate is very essential for developing new optical materials in UV range. In this paper, the birefringence values of five lead borates, Pb₈B₉O₂₁F, PbBiBO₄, Pb₃BO₄F, Pb₆B₃O₁₀Cl, and Pb₂BO₃F with network B–O structure or isolated BO₃ groups, are calculated by the first principle method. The calculations show that PbBiBO₄, Pb₃BO₄F, and Pb₂BO₃F have the large birefringence, greater than 0.1. Pb₂BO₃F, especially, is the first compound with large birefringence above 0.08 among positive uniaxial borate crystals. It is found that the parallel arrangement of fundamental building units is not the only light anisotropy active character. In the further research of Pb₂BO₃F, polarization disproportionation via a visualized model is first put forward for identifying the origin of large birefringence, which will be helpful to search for new optical materials with suitable birefringence