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Cr2B is Khatyrkite structured and crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Cr is bonded in a 4-coordinate geometry to four equivalent B atoms. All Cr–B bond lengths are 2.20 Å. B is bonded in a 10-coordinate geometry to eight equivalent Cr and two equivalent B atoms. Both B–B bond lengths are 2.14 Å.
Cr2B is Khatyrkite-like structured and crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. there are two inequivalent Cr sites. In the first Cr site, Cr is bonded in a 4-coordinate geometry to four equivalent B atoms. There are two shorter (2.19 Å) and two longer (2.20 Å) Cr–B bond lengths. In the second Cr site, Cr is bonded in a 4-coordinate geometry to four equivalent B atoms. There are two shorter (2.19 Å) and two longer (2.20 Å) Cr–B bond lengths. B is bonded in a 10-coordinate geometry to eight Cr and two equivalent B atoms. Both B–B bond lengths are 2.11 Å.
Endowing functional properties with mechanical responses in traditional metals has been a frontier topic, akin to transforming base metal into gold. Chromium and its alloys, with their functional deficiencies and limited ductility, serve as typical examples. Herein, we report a Cr96Fe4Ge1.3B1 alloy that unifies low thermal expansion (LTE, αl = 1.79 × 10-6 K-1, 200 − 315 K) with exceptional toughness (240.2 J·cm-3). The enhancement in mechanical responses is primarily attributed to layered Cr2B intermetallic precipitates, which ameliorate interfacial cohesion and simultaneously refine the grain structure. The weakened interlayer interactions within the Cr-B layers facilitate the nucleation and movement of numerous tiny stacking faults in precipitates, efficiently alleviating strain energy and resulting in marked work-hardening ability. Additionally, antiferromagnetic fluctuations in the BCC matrix contribute to the unique LTE behavior. This paves the way for the design of high-performance alloys featuring layered-symmetry precipitates.