Solid solution range of boron, microhardness and oxidation resistance of the perovskite type RERh₃B_x (RE = Gd, Y, Sc) compounds

Polycrystalline samples of RERh₃B_x (RE = Gd, Y, Sc), which consists of a reactive RE and high melting point Rh and B elements, are successfully synthesized by the arc melting method. RERh₃B_x compounds have the perovskite type cubic structure (space group Pm3m). Perovskite type phases of GdRh₃B_x and YRh₃B_x exist in the range of approximately 0.444≤x≤1.000. On the other hand, phase of ScRh₃B_x exists in the range of 0≤x≤1.000 (0 to 20 mol% B). ScRh₃, in the case of x = 0, has AuCu₃ type structure; its space group is also Pm3m. The lattice parameter a in RERh₃B_x depends on x and the value of a increases with increasing boron content x. The value of Vickers microhardness of the RERh₃B_x at room temperature ranges from 6 to 10 GPa. According to thermo-gravimetric and differential thermal analysis for RERh₃B_x (RE = Gd, Y) heating up to 1200 °C in air, a mixed phase of REBO₃ and Rh is identified as an oxidized product. In the case of ScRh₃B, the oxidized product consists of Rh, Sc₂O₃ and ScBO₃.