Unveiling pressure-induced anomalous shear behavior and thermoelasticity of α-Fe₂O₃ hematite at high pressure

Hematite (α-Fe₂O₃), as an important end-member of FeO-Fe₂O₃ series, has garnered particular interest for its peculiar high pressure-temperature (P-T) behavior, structural stability and elasticity, and the unclear role of Fe³⁺ in the nature and dynamics of the Earth's mantle. Here, we report a pronounced pressure-induced anomaly in the shear behavior of hematite at room temperature and ∼3.5 GPa owing to the (weak)ferromagnetic-to-antiferromagnetic Morin transition driven by pressure and temperature. Unexpectedly, this phase-transition-driven anomalous behavior at high P-T is absent in the compressional velocities. The bulk and shear moduli, as well as their pressure and temperature dependences for Fe₂O₃ hematite are reported, yielding K  = 235.5(8) GPa, G  = 88.0(3) GPa, әK /әP = 3.29(25), dG/dP = 1.36(10), әK /әT = -0.027(2) GPa/K, and әG/әT = -0.019(1) GPa/K. These findings and high-P thermoelasticity will be of significant importance for good understanding of the underlying mechanism for phase-transition-induced anomaly at high pressures and temperatures in the shear behavior of Fe-O materials.