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

摘要

The novel oxychloride BaBi(SeO3)(2)Cl with polar crystal structure was first synthesized by using hydrothermal method at a mild temperature of 200 degrees C. It crystallizes in the orthorhombic Cmc2(1) (36) space group with cell parameters of a = 5.2804(2) angstrom , b = 20.0535(9) angstrom, c = 6.9070(3) angstrom, V = 731.39(5) angstrom(3), and Z = 4. The compound features a two-dimensional [Bi(SeO3)(2)Cl](2-) anionic layer structure stacking along the crystallographic b-axis direction. Within the [Bi(SeO3)(2)Cl](2-) layer, BiO4 quadrangular pyramids bridge two types of Se(1)O-3 and Se(2)O-3 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)(2)Cl](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)(2)Cl 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.