Equation of state and high-pressure phase behaviour of SrCO<sub>3</sub>

Abstract

Abstract. The high-pressure phase transition of strontianite (SrCO3) 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 SrCO3 in the low pressure aragonite-type phase Pmcn (62) up to about 26 GPa. Above this pressure, SrCO3 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 SrCO3 yields K0=62.7(6) GPa and K0′=3.2(1), and for the high-pressure phase this yields K0=103(10) GPa and K0′=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 SrCO3 above 26 GPa and provide important structural parameters for this phase.

Orthocarbonates of Ca, Sr, and Ba—The Appearance of sp3-Hybridized Carbon at a Low Pressure of 5 GPa and Dynamic Stability at Ambient Pressure

“…The calculated equilibrium curves of aragonite and postaragonite structures of SrCO 3 and BaCO 3 were almost independent of temperature (Figure S4b and d). The pressure of the phase transition was around 17 GPa for SrCO 3 and around 7 GPa for BaCO 3 , which agreed with the available experimental results for these compounds. − …”

Structural, Physical, and Thermodynamic Properties of Aragonitic CaxSr1–xCO3 Solid Solutions

“…The experimentally obtained bulk modulus for the Ca 0.8 Sr 0.2 CO 3 and Ca 0.5 Sr 0.5 CO 3 composition is in good agreement with the data from the DFT-based calculations. The bulk modulus obtained for the equimolar solid solution is significantly lower than expected from a linear interpolation between the end-member carbonates, strontianite ( K 0 ≈ 63 GPa) and aragonite ( K 0 ≈ 67 GPa). ,,, While Dudnikova et al predicted a decrease in the bulk modulus of ≈1 GPa for the Ca 0.5 Sr 0.5 CO 3 solid solution relative to the ideal value, we experimentally determined a difference of ≈10 GPa. This clearly shows the limitations of the force field used by Dudnikova et al…”

Crystal Structure of BaCa(CO3)2 Alstonite Carbonate and Its Phase Stability upon Compression

“…These experimental results compare well with those obtained from theoretical calculations: V 0 = 1608.0(1) Å 3 , B 0 = 64.25(4) GPa, and B 0 ′ = 3.99(1). The bulk modulus lies in between those of the two end-member carbonates: 67(2) GPa for CaCO 3 calcite, 66.5(7) GPa ( B ′ 0 = 5.0(1)) for CaCO 3 aragonite and 48(1) GPa for BaCO 3 witherite, and it is comparable to the 62.7(6) GPa of SrCO 3 strontianite. , In other words, our data evidences that BaCa­(CO 3 ) 2 alstonite is more compressible than all of the divalent metal carbonates and silicate-carbonates except witherite. ,,− …”

“…The bulk modulus lies in between those of the two end-member carbonates: 67(2) GPa for CaCO 3 calcite, 49 66.5( 7) GPa (B′ 0 = 5.0(1)) for CaCO 3 aragonite 50 and 48(1) GPa for BaCO 3 witherite, 51 and it is comparable to the 62.7(6) GPa of SrCO 3 strontianite. 51,52 In other words, our data evidences that BaCa(CO 3 ) 2 alstonite is more compressible than all of the divalent metal carbonates and silicate-carbonates except witherite. 12,48,52−54 Taking into account the good agreement found between experimental and theoretical data in (i) lattice parameters and atomic positions at ambient conditions (see Tables 2 and 3) and (ii) the unit-cell compressibility behavior within the 0−9 GPa pressure range, we use data from our DFT simulations to study the variation of bond distances and polyhedral compressibilities with pressure.…”