Nonstoichiometric perovskite type-GdRh₃B_x compound and it's relation of boron content to hardness and oxidation resistance

Polycrystalline samples of GdRh₃B_x, which consists of highly reactive (Gd) and high melting (Rh, B) elements, have been successfully synthesized by arc melting method. Extreme evaporation of the constituent elements has not been observed. Compound of GdRh₃B_x has perovskite type cubic structure (space group: Pm3m). Perovskite-type GdRh₃B_x exists in the range of x=1.000 (20 atom% B) and 0.444 (10 atom% B). Lattice parameter of α in annealed GdRh₃B_x depends on x, and varies lineary from α=0.41831 (6)nm (x=1.000) to 0.4121(1) nm (x=0.444). The TG curve indicates that the onset-temperature of oxidation for GdRh₃B_1.000 is 567.3 °C and for GdRh₃B_0.706 is 611.3 °C, respectively. Weight gain by heating in air up to 1200°C for GdRh₃B_1.000 (20 atom% B) is 6.83% and for GdRh₃B_0.706 (15 atom% B) is 8.61%, respectively. The former value for stoichiometric compound is smaller than the latter. Both samples decompose to GdBO₃ and Rh after oxidation. The micro-Vickers hardness of the annealed GdRh₃B_x increases with increasing B content in the range of x=1.333-0.444, for example hardness of the annealed GdRh₃B_1.000 (20 atom%B) is 4.2(± 0.10) GPa.