Synthesis, Structure, and Properties of the Non-Centrosymmeteric Compound LiNaRbB5O8(OH)2

A new non-centrosymmetric hydroxyl alkali metal borate LiNaRbB5O8(OH)2 has been grown under mild hydrothermal conditions at 220 °C. LiNaRbB5O8(OH)2 belongs to the orthorhombic space group Aba2, with a = 11.3017(5) A, b = 10.9956(5) A, c = 9.2860(4) A, and Z = 2. The crystal structure of LiNaRbB5O8(OH)2 consists of Li/Na–O, Rb–O polyhedra, and [B5O8(OH)2]3– groups. The transmittance spectrum of the LiNaRbB5O8(OH)2 exhibits an absorption edge less than 200 nm in the UV region. The powder second-harmonic generation coefficient in LiNaRbB5O8(OH)2 is about one-third that of KH2PO4 (KDP) based on the Kurtz-Perry method. First principle calculations based on band structure, density of states, and optical properties are used to better understand the relationship between electronic structure and optical properties.