Effect of B and C concentration on crystallization and properties of HoNi2B2C

The effect of boron and carbon deviation from the stoichiometric composition on the crystallization behavior and superconducting properties of the HoNi2B2C compound was studied at polycrystalline HoNi2B2+xC and HoNi2B2C1+y samples. It was detected that x, y > 0 causes primary phase HoB2C2 precipitation prior to the HoNi2B2C growth, whereas depletion of B or C (x, y < 0) results in an increased fraction of eutectics containing additional Ni-rich phases. The shift of melt composition also leads to a composition variation of the HoNi2B2C compound within its homogeneity range. Accordingly, HoNi2B2C samples show pronounced re-entrant superconducting behavior in a wide range of B content (0 < x < 0.1), whereas small deviations of C from the stoichiometry (0 < y < 0.03) results in a loss of superconducting properties.