Structure and optical properties of a new borate K2Ba4Ga4Li2B6O21

Abstract A new borate crystal, K 2 Ba 4 Ga 4 Li 2 B 6 O 21 , was successfully synthesized and grown by the spontaneous crystallization with K 2 O–B 2 O 3 –LiF flux. It belongs to a hexagonal space group P 6 ¯ 2 c with cell parameters of a = 8.6544(4) A, c = 16.9226(16) A, and Z = 2. The fundamental building units in the structure are the planar BO 3 triangle, tetrahedral GaO 4 and LiO 4 anionic groups. These anions jointed together by corner-sharing O atoms to form a [ Ga 2 Li ( BO 3 ) 3 ] 2 - ∞ 2 layer. The neighboring layers are linked with apical O atoms of GaO 4 and LiO 4 groups in the c direction to build up a three-dimensional framework. The structure is closely related to that of the nonlinear optical crystal K 2 Al 2 B 2 O 7 with two Ga and one Li atoms occupying the three Al sites and simultaneously a mixed K + /Ba 2+ and a pure Ba 2+ cation replacing the two K sites in an ordered fashion. Second-harmonic generation (SHG) test indicates that the SHG signal of K 2 Ba 4 Ga 4 Li 2 B 6 O 21 crystal is about half as large as that of KDP standard. The UV–Vis–NIR diffuse reflectance spectra shows that the crystal has a high transmission ranging from 400 nm to 1200 nm with a UV cut-off edge at 226 nm.