Large Magnetocaloric Effect in Li<sub>3</sub>K<sub>9</sub>Gd<sub>3</sub>(BO<sub>3</sub>)<sub>7</sub> Crystal Featuring Sandwich-Like Three-Dimensional Framework
Wang Liu, Fei Liang, Yuwei Chen, Huimin Song, Jingcheng Feng, Jun Shen, Zheshuai Lin, Heng Tu, Guochun Zhang
Abstract
A new Gd-based borate crystal, Li3K9Gd3(BO3)7, has been successfully obtained via the high-temperature solution method using Li2O–K2O–B2O3 self-flux. It crystallizes in monoclinic space group P2/n (no. 10) with lattice parameters a = 11.3454(6) Å, b = 9.9881(4) Å, c = 11.4467(7) Å, α = γ = 90 o, β = 114.782(7) o, and Z = 2. Li3K9Gd3(BO3)7 exhibits an intriguing sandwich-like three-dimensional (3D) framework constructed from [Gd–B–O]∞ layers, KOn (n = 6 and 8) polyhedra, and LiO4 tetrahedra, in which [Gd–B–O]∞ layers are built from two types of GdO8 polyhedra and triangular BO3 units. Magnetic measurements showed that Li3K9Gd3(BO3)7 exhibits a large magnetocaloric effect with −ΔSm = 39.3 J kg–1 K–1 at 2.0 K for ΔH = 7 T, which is slightly higher than that of the commercial gadolinium gallium garnet under the same conditions. The powder X-ray diffraction, infrared spectrum, and UV–vis–NIR diffuse reflectance spectrum were also performed to characterize Li3K9Gd3(BO3)7. The electronic band structures, partial density of states, and refractive indices of Li3K9Gd3(BO3)7 were investigated via the first-principle calculations.