BaBi(SeO3)2Cl: a new polar material showing high second-harmonic generation efficiency enhanced by constructive alignment of chloride ions

Abstract

The novel oxychloride BaBi(SeO₃)₂Cl with polar crystal structure was first synthesized by using hydrothermal method at a mild temperature of 200 °C. It crystallizes in the orthorhombic Cmc2₁ (36) space group with cell parameters of a = 5.2804(2) Å, b = 20.0535(9) Å, c = 6.9070(3) Å, V = 731.39(5) ų, and Z = 4. The compound features a two-dimensional [Bi(SeO₃)₂Cl]²⁻ anionic layer structure stacking along the crystallographic b-axis direction. Within the [Bi(SeO₃)₂Cl]²⁻ layer, BiO₄ quadrangular pyramids bridge two types of Se(1)O₃ and Se(2)O₃ triangular pyramid through corner-sharing manner into a [Bi(SeO₃)₂]⁻ chain. The [Bi(SeO₃)₂]⁻ chains are aligned along c-axis direction with chloride ions adjacent to bismuth cations, and the 2D [Bi(SeO₃)₂Cl]²⁻ forms. As a consequence, local dipole moments of the building block layers are arranged in a constructive fashion, which is favourable to enhance the second-order nonlinear properties of materials. Powder Kurtz–Perry method was utilized to evaluate the second-harmonic generation (SHG) efficiency, indicating a strong SHG effect (about 16 times that of KH₂PO₄ (KDP) reference). More excitingly, BaBi(SeO₃)₂Cl can achieve type I phase-matching, which make the compound feasible for practical applications. In addition, first-principles density functional theory (DFT) calculations were also performed to illustrate the relationships between crystal structure and optical properties.