Manipulation of birefringence via substitution of Sr2+ by Pb2+ based on the structure model of LiSr1−xPbxBO3 (0 ≤ x ≤ 0.5)

Abstract

A series of LiSr_1−xPb_xBO₃ (x = 0.138, 0.285, 0.320, 0.379, 0.417, and 0.5) crystals have been obtained through a high-temperature solution reaction with spontaneous nucleation technique, and the crystal structures were solved from single-crystal X-ray diffraction data. Through a great deal of experiments, it was determined that the maximum value of x cannot be greater than 0.5 possibly because the Sr/Pb–O bond length and the equivalent isotropic displacement parameter of O(3) atoms continuously increased with the increased ratio of Pb²⁺ cations. It is found that when the Sr atoms were partially substituted with Pb atoms with optical anisotropies, the birefringence improved from 0.0494 at 1064 nm in LiSrBO₃ to 0.0721 at 1064 nm in LiSr_0.5Pb_0.5BO₃. Based on the first-principles and real-space atom-cutting method, the origin of birefringence was attributed to the Pb²⁺ cations and (BO₃)³⁻ groups in LiSr_0.5Pb_0.5BO₃. The infrared spectrum properties and thermal behavior were also reported.