Equation of state and high-pressure phase behaviour of $SrCO_{3}$

The high-pressure phase transition of strontianite $(SrCO_{3})$ was investigated at ambient temperature by means of powder and single-crystal X-ray diffraction. The samples were compressed in a diamond anvil cell to a maximum pressure of 49 GPa. Structure refinements confirm the existence of $SrCO_{3}$ in the low pressure aragonite-type phase Pmcn (62) up to about 26 GPa. Above this pressure, $SrCO_{3}$ transforms into a high-pressure phase with post-aragonite crystal structure Pmmn (59). Fitting the volume extracted from the compression data to the third-order Birch–Murnaghan equation of state for the low-pressure phase of $SrCO_{3}$ yields $K_{0}$=62.7(6) GPa and $K′_{0}$=3.2(1), and for the high-pressure phase this yields K$_{0}$=103(10) GPa and $K′_{0}$=2.3(6). The unit cell parameters change non-uniformly, with the c axis being 4 times more compressible than the a and b axes. Our results unequivocally show the existence of a Pmmn structure in $SrCO_{3}$ above 26 GPa and provide important structural parameters for this phase.