Borides borocarbides

Table 1. Metal Borides and Borocarbides Structure Types and Representatives with B Chains... 

Rare-earth (and actinide)-B-carbon compounds resemble metal borides in B-rich carboborides, whereas the physical and structural properties of C-rich borocarbides tend to a more earbide-like behavior (which will not be covered in this context). 

The reduction of a metal oxide by a mixture of B and C is easier than the reduction by the borothermic process described above. The rate of reduction depends on the removal of CO, so operation under vacuum increases the rate and allows the reaction to proceed at a lower T than the borothermic process. The metal oxide may be volatile and the borides can be contaminated by C. Accordingly, this method is not suitable for preparing pure alkaline-earth and rare-earth hexaborides because in all cases borocarbides of formula MBg C, (e.g., M = Sr, Eu, Yb) are formed . 

Nitrides, carbides, and borides of iron (as well as carbonitrides and other possible mixed compounds such as borocarbides or boronitrides) are... 

Superconductivity in the multiphase quaternary borocarbide system Y-Ni-B-C has been recently reported [141,142], Earlier work on valence fluctuations in ternary borides RENiaB were studied and in the case of YNi4B, a weak but reproducible signal of superconductivity at Tc of 12 K was observed. This is the first report or discovery of a ternary superconducting phase of the elements Y, Ni and B with a high Tc value (Fig. 12.27). 

In this section, I focns on the ternary rare earth boride compounds that have particnlar interest for their stmctural features or physical properties. Rare earth borocarbides are described in a separate section, after the section on rare earth carbides. 

The rare earth borides, carbides, and nitrides aU have compounds that manifest superconductivity, fundamental magnetic transitions, and other interesting phenomena such as strongly correlated heavy fermion behavior. Some of the rare earth transition metal borocarbides such as RTr2B2C have shown fascinating properties where magnetism and superconductivity phenomena coexist. 

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