Equation of state of a natural chromian spinel at ambient temperature

Abstract

A natural chromian spinel with the composition (Mg 0.48(3) Fe 0.52(3) )(Fe 0.06(1) Al 0.28(1) Cr 0.66(2) ) 2 O 4 was investigated up to 15 GPa via synchrotron X-ray diffraction with a diamond-anvil cell at room temperature. No phase transition was clearly observed up to the maximum experimental pressure. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yielded an isothermal bulk modulus (K T0 ) of 207(5) GPa and its first pressure derivative (K T0′ ) of 3.2(7), or K T0 = 202(2) GPa with K T0′ fixed as 4. With this new experimental result and the results on some natural chromian spinels in the literature, a simple algorithm describing the relation between the K T0 and the compositions of the natural chromian spinels was proposed. To examine this algorithm further, more compression experiments should be performed on natural chromian spinels with different chemical compositions.