Extraordinary local structure deformation of superhard tungsten tetraboride under compression

Abstract In this work, we explore the deformation mechanism in superhard material candidate WB4 using high-pressure X-ray absorption fine structure spectroscopy up to 47 GPa. By examining the changes of local W–B bonding parameters with pressure, we find an extraordinary two-stage deformation process in WB4. First, a sudden stepwise increase of the W–B bond disorder with a concomitant drop of the white-line intensity at ∼21 GPa. It indicates the occurrence of boron layers distortion which can be initiated by W–B bond weakening due to W 5d electron depletion. This transition can be responsible for the anomalous c-axis softening as observed by X-ray diffraction. Second, a marked decrease of W–B bond disorder at ∼42 GPa. It suggests a tendency for the boron layers to become flatter, which can be associated with W–B bond maximization to accommodate high compression. These peculiar structural rearrangements and bonding optimization are not observed in other transition metal borides such as ReB2. Our findings offer key insights into the mechanism of the constrained three-dimensional boron network in WB4 to withstand deformation under compression, which can facilitate the bottom-up design of novel WB4-based materials with tailored mechanical properties.