Abstract
A mixed alkaline-earth powellite, Ca0.84Sr0.16MoO4 (calcium strontium molybdate), was synthesized by a flux method and its crystal structure was solved using single-crystal X-ray diffraction (SC-XRD) data. The compound crystallized in the I41/a space group as with a typical CaMoO4 powellite, but with larger unit-cell parameters and unit-cell volume as a result of the partial incorporation of larger Sr cations into the Ca sites within the crystal. The unit cell and volume were well fitted with the trendline calculated from literature values, and the powder X-ray diffraction (P-XRD) pattern of the ground crystal is in good agreement with the calculated pattern from the solved structure.
Highlights
Powellites doped with rare-earth elements have broad absorption bands and fluorescence emissions in the visible to near-infrared range (Kim & Kang, 2007; Lei & Yan, 2008; Schmidt et al, 2013), and isostructural BaMoO4 and SrMoO4 crystals have high photoluminescence emission in the visible spectral region (Bi et al, 2008; Lei et al, 2010)
Alkaline-earth powellites crystallize during the development of the ceramic-waste forms for radionuclides in the high-level waste (HLW) raffinate stream from aqueous reprocessing of used nuclear fuel (Crum et al, 2019; Peterson et al, 2018)
Powellite crystallizes in the tetragonal space group I41/a and contains Ca2+ cations coordinated by eight [MoO4]2À tetrahedra, sharing an oxygen atom with each tetrahedron
Summary
Powellite (CaMoO4) is a naturally occurring mineral with the scheelite (CaWO4) structure and has been studied for different applications including laser materials, phosphors, catalysts, electrodes, and radionuclide waste forms (Kato et al, 2005; Lei & Yan, 2008; Rabuffetti et al, 2014; Peterson et al, 2018; Ryu et al, 2007). Various methods have been used to synthesize scheelitestructured crystals including vapor diffusion sol-gel (VDSG), hydrothermal, molten salt reaction, Pechini, sonochemical, precipitation, solid-state, and pulsed-laser-induced methods (Culver et al, 2013; Lei & Yan, 2008; Wang et al, 2006; Kodaira et al, 2003; Geng et al, 2006; Ahmad et al, 2006; Ryu et al, 2007). Ryu et al (2007) used the pulsed-laser ablation method to synthesize spherical powellite particles of 16–29 nm
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