The MAX phase borides Zr2SB and Hf2SB

Zr2SB and Hf2SB were synthesized via solid-state reactions and the crystal structures were determined by powder X-ray diffraction. Both compounds crystallize in the hexagonal Cr2AlC-type structure (P6(3)/mmc; Z = 2; Zr2SB a = 3.5001(1) angstrom, c = 12.2712(2) angstrom; Hf2SB a = 3.4671(1) angstrom, c = 12.1046(2) angstrom). The lattice parameters and bond lengths are slightly longer and the M6X octahedra are less distorted compared to the known carbides. Resistivity and magnetic measurements reveal that Zr2SB and Hf2SB are good metallic conductors and Pauli paramagnets. Ab-initio DFT calculations of the electronic structure confirm the nonmagnetic metallic state and show mainly ionic bonds, which are weaker than in the carbides. The elastic constants indicate that Zr2SB and Hf2SB are brittle and exhibit a less two-dimensional character compared to other MAX phases.