Gadolinium-Rich Borate Gd17.33(BO3)4(B2O5)2O16 Exhibiting a Magnetocaloric Effect

A gadolinium-rich borate Gd17.33(BO3)4(B2O5)2O16 was successfully grown by the high-temperature solution method using the Rb2O–B2O3 flux. The crystal crystallizes in centrosymmetric space group C2/m with lattice constants a = 18.4300(2) Å, b = 3.7400(4) Å, c = 14.2047(16) Å, and β = 119.8550(12)°. Two different honeycomb-like [GdO] layers alternately arrange in the order ABAB forming the three-dimensional framework, in which the isolated [B2O5] and [BO3] units fill in channels of the 12-membered and 10-membered [GdO] polyhedral rings, respectively. The UV cutoff edge of Gd17.33(BO3)4(B2O5)2O16 is less than 240 nm. The maximum −ΔSm,max is 26.53 J kg–1 K–1 or 174.70 mJ cm–3 K–1 (T = 4.4 K and ΔH = 7 T) as investigated by the isothermal magnetization method.