Growth and Physical Properties of RuB2 Crystal Obtained by High-Temperature Cu Solution Method

RuB2 (orthorhombic, Pmmn) crystals were grown using metal ruthenium and boron powders using a high-temperature Cu (atomic ratio Cu/Ru = 25.4) solution at 1573 ~ 1773 K, with 5 h keep-time under an Ar atmosphere. Single phase RuB2 crystals were obtained from the mixture ratios (B/Ru = 2.5 ~ 3.0). For B/Ru = 1.5 ~ 2.2, RuB2 crystals were formed as a mixed phase with Ru2B3 crystals. The hexagonal RuB2 crystals grew larger with the ratio of B/Ru = 2.5 ~ 3.0. The magnetic susceptibility of RuB2 showed diamagnetic behavior with almost no temperature dependence from room temperature down to about 80 K, at which a small jump is observed, and Curie-Weiss like paramagnetic behavior observed for further lower temperatures. The electrical resistivity showed low values below 0.142 Ωcm. Single crystals of RuB2 did not exhibit superconductivity down to temperatures as low as 1.8 K.