Pressure-induced spin pairing transition of Fe$^{3+}$ in oxygen octahedra

• DOI: 10.48550/arxiv.1710.03192
• Publication Date: 2017-01-01
• Authors: Denis M. Vasiukov; Leonid Dubrovinsky; Ilya Kupenko; Valerio Cerantola; Georgios Aprilis; Leyla Ismailova; Elena Bykova; Catherine McCammon; Clemens Prescher; A. I. Chumakov; Natalia Dubrovins...
• Keywords: Spin transition; Metastability; Ferroics

High pressure can provoke spin transitions in transition metal-bearing compounds. These are of high interest not only for fundamental physics and chemistry, but also may have important implications geochemistry geophysics the Earth planetary interiors. Here we carried out a comparative study pressure-induced compounds with trivalent iron, octahedrally coordinated by oxygen. High-pressure single-crystal Mössbauer spectroscopy data FeBO$_3$, Fe$_2$O$_3$ Fe$_3$(Fe$_{1.766(2)}$Si$_{0.234(2)}$)(SiO$_4$)$_3$ presented together detailed analysis hyperfine parameter behavior. We argue that $ζ$-Fe$_2$O$_3$ is an intermediate phase reconstructive between $ι$-Fe$_2$O$_3$ $θ$-Fe$_2$O$_3$ question proposed perovskite-type structure $ζ$-Fe$_2$O$_3$.The structural show closely related to volume iron octahedron. The starts when volumes reach 8.9-9.3 Å$^3$, which corresponds pressures 45-60 GPa, depending on compound. Based phenomenological arguments conclude proceed as first-order magnetically-ordered An empirical rule prediction cooperative behavior at proposed. instability octahedra, strong interactions them vicinity critical volume, trigger metastable phase. find isomer shift ions depends linearly octahedron approximately same coefficient, independent particular and/or oxidation state. For eight-fold Fe$^{2+}$ observe significantly weaker nonlinear dependence.