Crystal structure of radium sulfate: An X-ray powder diffraction and density functional theory study

Radium-barium sulfate (Ra0.76Ba0.24SO4) powder was examined using X-ray Diffraction (XRD) technique and its crystal structure was optimized using Density Functional Theory (DFT). XRD data show that radium and barium sulfate form a solid solution and that Ra0.76Ba0.24SO4 is orthorhombic and isostructural with pure RaSO4, barite (BaSO4), celestite (SrSO4) and anglesite (PbSO4), crystallizing in the space group Pmna (No. 62). The unit cell parameters of the Ra0.76Ba0.24SO4 crystal have been determined using Rietveld refinement and were extrapolated to unit cell parameters of the pure RaSO4 phase using Vegard's law: a=9.129(8), b=5.538(3), c=7.313(5) Å. DFT geometry optimization was used to derive atomic coordinates and interatomic distances in both Ra0.76Ba0.24SO4 and pure RaSO4. The experimental and DFT geometry optimization results obtained in this work are in good agreement with each other, and furthermore with literature data.