Crystal Chemistry and Thermodynamics of HREE (Er, Yb) Mixing in a Xenotime Solid Solution

Abstract

Rare earth elements (REEs), the 15 naturally occurring lanthanides plus yttrium and scandium, are ubiquitously used in modern life as they are critical components of many advanced devices and technologies. However, the demand for REEs is not equal, with the heavy rare earth elements (HREEs) having a higher demand. Xenotime (HREEPO4) is an important HREE ore mineral and globally is an economical source of HREE. Most of the crystallographic and thermodynamic properties of xenotime endmembers have been elucidated by calorimetric, solubility, and high-pressure studies. Yet, in natural systems, endmembers are rarely encountered, and instead, REE solid solutions are more commonly observed. In this work, we characterize the crystal chemistry, thermodynamics of HREE mixing, and high-temperature material behaviors and thermochemistry of a synthetic erbium (Er)–ytterbium (Yb) binary xenotime solid solution (Er(x)Yb(1–x)PO4) using a suite of experimental techniques, including X-ray fluorescence spectroscopy, synchrotron X-ray powder diffraction implemented with Rietveld analysis, Fourier transform infrared spectroscopy coupled with attenuated total reflectance, Raman spectroscopy, thermogravimetric analysis coupled with differential scanning calorimetry, and high-temperature oxide melt drop solution calorimetry. Our results shed light on the formation of natural xenotimes and lay the foundation for their industrial applications as thermal coating materials.

How hydrothermal synthesis improves the synthesis of (Zr,Ce)SiO4 solid solutions

“…A second mass loss (≈4 wt%) was observed up to about 480 °C. It could be explained by the significant release of the "structural" water confined into the [001] channel, more strongly interacting with the structure of the sample, as suggested by Strzelecki et al 56,61 Then, the additional mass loss (≈2 wt%) observed up to 1000 °C may be due to the continuous release of the most strongly bonded water molecules among with the hydroxyl groups. These results agreed well with the results recently obtained by Guo et al 62 for TGA of synthetic coffinite USiO 4 samples and by Estevenon et al 11,12 for HfSiO 4 and ThSiO 4 samples.…”

Crystal chemistry and thermodynamic properties of zircon structure-type materials

“…In this review, we evaluated recent advances in the crystal chemistry and thermodynamic properties of zircon structure-type materials. We focused on empirically derived structureproperty relationships, which can be used to obtain thermodynamic functions and support their (Langmuir 1978;Langmuir and Chatham 1980;Ellison and Navrotsky 1992;Grenthe et al 1993;Mazeina et al 2005;Navrotsky and Ushakov 2005;Szenknect et al 2013;Guo et al 2015Guo et al , 2016aStrzelecki et al 2020b), orthochromates (ACrO4) (Lee and Nassaralla 2006), orthovanadates (AVO4) (Dorogova et al 2007), and orthophosphates (APO4) (Marinova et al 1973;Ushakov et al 2001;Strzelecki et al 2022)…”

“…While impurities, such as He, can reside in the interstitial sites, it is much more common for impurities to be introduced through substitution of cations over either TO4 (e.g., Ga 3+ , Ti 4+ , W 6+ ) or MO8 (e.g., Na + , Sr 2+ , Zn 2+ ) sites (Speer 1982b). Additionally, water molecules can also be incorporated to considerable levels, sometimes greater than 0.5 mols per formula unit (Guo et al 2015;Shelyug et al 2021;Strzelecki et al 2021Strzelecki et al , 2022. The water molecules are confined to the [001] structural channels, which was initially hypothesized by Janeczek (1991) and Kijkowska (2003) confirmed the confined water in orthosilicates-orthophosphates based solid solutions ThxEr1-…”

“…Water molecules confined in the [001] channel had significant effects on both the dehydration and structural response on heating (Shelyug et al 2021;Strzelecki et al 2021Strzelecki et al , 2022.…”

“…However, recent work Jenkins and Glasser (2003) and experimentally derived ones (Robie and Hemingway 1995;Navrotsky et al 2015;Gysi et al 2016Migdissov et al 2016;Van Hoozen et al 2020). A new set empirical S°298 K -Vm linear equations were thus proposed by Strzelecki et al (2022) to include phosphate minerals and further extended to all minerals. Lastly, knowing both the ΔGf and ΔHf values for a given material, an indirect method for determining the S° value is to calculate ΔSf through rearrangement of the Gibbs Free Energy equation (∆𝐺 * = ∆𝐻 * − 𝑇∆𝑆 * ) and then to access the S° value for a given compound.…”