Boron nonstoichiometry, hardness and oxidation resistance of perovskite-type CeRh3Bx (x = 0-1)

We report synthesis of perovskite-type boride CeRh3Bx using the arc melting method. The samples are characterized by powder X-ray diffraction which shows that the crystal structure of CeRh3Bx belongs to the cubic system (space group: Pm3m) in the range of 0 < x ≤ 1. Furthermore, CeRh3 (x = 0) has the ordered AuCu3-type structure (space group: Pm3m). As a result, CeRh3Bx exists in a wide range of nonstoichiometric boron concentration 0 ≤ x ≤ 1 with the space group Pm3m. The lattice parameter, a, changes almost linearly with x, varying from 0.4015(1) nm (x = 0) to 0.4180(1) nm (x = 1.0). The micro-Vickers hardness of the CeRh3Bx for x = 0 (0 at.%B), 0.210 (5 at.%B), 0.444 (10 at.%B), 0.706 (15 at.%B) and 1.0 (20 at.%B) are 2.0 ± 0.1, 4.3 ± 0.2, 1.8 ± 0.2, 5.5 ± 0.1 and 6.5 ± 0.2 GPa, respectively. Thermo-gravimetric analysis was done to study the oxidation resistance of the samples in air. It reveals that oxidation begins at 502 and 513 K for x = 0 and 1.0, respectively. A mixed phase of CeO2 + Rh is identified as an oxidized product for all samples.