Seven-Coordinated High-Pressure Phase of CrSb2 and Experimental Equation of State of MSb2 (M = Cr, Fe, Ru, Os)

The MSb2 compounds with M = Cr,Fe, Ru, and Os have been investigated under high pressuresby synchrotron powder X-ray diffraction. All compounds, except CrSb2, were found to retain the marcasite structure up to the highestpressures (more than 50 GPa). In contrast, we found that CrSb2 has a structural phase transition around 10 GPa to a metastable,MoP2-type structure with Cr coordinated to seven Sb atoms.In addition, we compared ambient temperature compression with laser-heatingexperiments and found that laser-heating at pressures below and abovethis phase transition results in the known CuAl2-type structure.Density functional theory calculations show that this tetragonal structureis the most stable in the whole pressure interval. However, a crossingof the marcasite's and MoP2-like structure'senthalpies occurs between 5 and 7.5 GPa, which is in good agreementwith the experimental data. The phase transition to the MoP2-type structure observed in this work opens up for discovering othercompounds with this new transition pathway from the marcasite structure.High-pressure experiments reveal a structuraltransitionfor marcasite CrSb2 to a MoP2-type structureat 10 GPa, where the coordination number for chromium increases from6 to 7. High-pressure, high-temperature studies reveal that both themarcasite and the MoP2-type structure transform into the8-coordinated CuAl2-type structure. Structural compressionstudies on CrSb2, FeSb2, RuSb2, andOsSb(2) show an increase in bulk moduli going from Cr toFe and then to Ru and Os.