Large Magnetocaloric Effect in Li₃K₉Gd₃(BO₃)₇Crystal Featuring Sandwich-Like Three-Dimensional Framework

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.