Unusual suppression of tungsten 5delectron depletion in superhard tungsten tetraboride solid solution with chromium under compression.

The lattice compressibility and deformation in superhard tungsten tetraboride (WB4) solid solution with chromium (Cr) are investigated by high-pressure x-ray diffraction and x-ray absorption fine structure (XAFS) spectroscopy up to 54 GPa. In contrast to pure WB4, thec-axis softening is effectively suppressed in W0.9Cr0.1B4, and less compressibility is shown for thea- andc-axes in the entire pressure range. Meanwhile, the white-line peak of W L3-edge XAFS in W0.9Cr0.1B4shows an absence of the sudden intensity drop as previously observed in WB4at ∼21 GPa, suggesting a strong inhibition of W 5delectron depletion. This phenomenon is followed by an initial increase and then decrease for the W-B bond disorder, with the magnitude greatly lower than that of WB4. Besides the apparent atomic size mismatch effect, these results imply that addition of Cr, which has the same number of valence electrons as W, can introduce an unexpected electronic structure change to strengthen the W-B bond via a modification of W vacancies and B trimers distribution in WB4lattice. Our findings point out the great significance to precise manipulation of the intrinsic W vacancies and B trimers through different solute atoms to rational optimization of WB4hardness.