Abstract
The orthorhombic-hexagonal phase transformation in the system BaCO3-SrCO3 has been investigated to 7000 bar by differential thermal analysis. The pressure dependence of the orthorhombic-hexagonal transformation temperature Tpmay be represented by the polynomial Tp=933.4−443.3 · XBaCO3+323.7 · XBaCO3+P(8.59−2.48)·XBaCO3 where XBaCO3=mol fraction of witherite, P the pressure in kbar and T the temperature in °C. Lattice parameters refined by powder X-ray diffraction measurements of the orthorhombic solid solution can be fitted to a linear relationship Vorthorh [A3]=259.30+XBaCO3 with no evidence of any excess volume. The experimental transformation temperatures are modeled by assuming a symmetric regular solution and a diffusionless transformation.
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