Possible Superhardness of CrB4

Abstract
Chromium tetraboride [orthorhombic, space group Pnnm (No. 58), a = 474.65(9) pm, b = 548.0(1) pm, c = 286.81(5) pm, and R value (all data) = 0.041], formerly described in space group Immm, was found not to be superhard, despite several theory-based prognoses. CrB4 shows an almost temperature-independent paramagnetism, consistent with low-spin CrI in a metallic compound. Conductivity measurements confirm the metallic character.