STATIC COMPRESSION OF α-FE2O3: LINEAR INCOMPRESSIBILITY OF LATTICE PARAMETERS AND HIGH-PRESSURE TRANSFORMATIONS

Abstract

The high-pressure behavior of α-Fe2O3 has been studied under static compression up to 60 GPa, using a laser-heated diamond anvil cell. Synchrotron-based angular-dispersive X-ray diffraction shows that the sample remains in the corundum structure up to 50 GPa, but with the appearance of coexisting diffraction lines from a high-pressure phase at pressures above 45 GPa. A least-squares fit of low-pressure phase data to an Eulerian finite-strain equation of state yields linear incompressibilities of Ka0=749.5 (± 18.4) GPa and Kc0= 455.7 (± 21.4) GPa, differing by a factor of 1.6 along the two directions. The enhanced compressibility of the c axis may lead to breaking of vertex- or edge-sharing bonds between octahedra, inducing the high-pressure phase transformation at 50 GPa. Analysis of linear compressibilities suggests that the high-pressure phase above 50 GPa is of the Rh2O3 (II) structure. Continuous laser heating reveals a new structural phase transformation of α-Fe2O3 at 22 GPa, to an orthorhombic structure with a=7.305(3) A, b=7.850(3) A, and c=12.877(14) A, different from the Rh2O3 (II) structure.