THE TERNARY-SYSTEM HOLMIUM BORON CARBON - ISOTHERMAL SECTION AT 1500-DEGREES-C

The phase equilibria in the ternary system holmium-boron-carbon have been investigated in the isothermal section at 1500 degree C. Samples were prepared by arc melting and subsequent annealing for 100 h under argon atmosphere at 1773 K. In addition to the already known phases (i. e. , HoB//2, HoB//4, HoB//6, HoB//1//2, HoB//6//6, B//1//3C//2, HoC//x, Ho//2C, Ho//2C//3, HoC//2, HoB//2C, and HoB//2C//2) two new carbides, Ho//1//5C//1//9 and Ho//5C//6, and five new ternary compounds, HoBC, Ho//2BC//3, Ho//5B//2C//5, Ho//5B//2C//6, and Ho//1//5B//2C//1//7, were identified. HoBC and Ho//2BC//3 present both low- and high temperature modifications. The crystal structures were determined for the phases HoBC (h. t. ), Ho//1//5C//1//9, Ho//5B//2C//5, Ho//5B//2C//6. For the other new compounds the unit-cell dimensions are given.