Crystal chemistry and thermodynamic properties of zircon structure-type materials

Abstract

Zircon-class ternary oxide compounds have an ideal chemical formula of ATO4, where A are commonly lanthanides and actinides, with T = As, P, Si, V. Their structure (I41/amd) accommodates a diverse chemistry on both A-and T-sites, giving rise to more than seventeen mineral end-members of five different mineral groups, and forty-five synthetic end-members.Because of their diverse chemical and physical properties, the zircon structure-types are of interest to a wide variety of fields and may be used as ceramic nuclear waste forms and as aeronautical environmental barrier coatings, to name a couple. To support advancement of their applications, many studies have been dedicated to the understanding of their structural and thermodynamic properties. The emphasis in this review will be on recent advances in the structural and thermodynamic studies of zircon structure-type ceramics, including pure endmembers (i.e., zircon (ZrSiO4), xenotime (YPO4)), and solid solutions (i.e., ErxTh1x(PO4)x(SiO4)1-x). Specifically, we provide an overview on the crystal structure, its variations and transformations in response to non-ambient stimuli (temperature, pressure and radiation), and correlation to thermophysical and thermochemical properties.

Synthesis and Characterization of Single Crystal Zircon-Hafnon Zr(1–x)Hf(x)SiO4 Solid Solutions and the Comparison with the Reaction Products of a TEOS-Based Hydrothermal Route

“…Furthermore, upon heating and crystallite growth hydroxyl groups began to leave Zr­(SiO 4 ) 1– x (OH) 4 x , because zircon can contain water (cf. e.g., refs − ). This process may have not come to an end at 1250 °C, because the weight loss graphs were still slightly declining (cf.…”

Phonon softening induced phase transition of CeSiO4: a density functional theory study

“…1), have emerged as a promising candidate matrix for immobilizing minor actinides due to its remarkable attributes, such as minimal chemical reactivity, low solubility, and robust resistance to radiation-induced damage. 2,14–17 Additionally, aside from its role as a nuclear waste disposal matrix, zircon-structured phase is also being considered as an alteration form during the long-term nuclear waste storage. 18 Most actinide nuclei and the decay daughter nuclei have long half-lives, such as T 1/2, Pu-241 = 14.4 years and its second daughter nuclei T 1/2, Np-237 = 2.1 million years.…”

“…29 To date, there is also only one experimental study of CeSiO 4 under high pressure. 30 In practice, stetindite (CeSiO 4 ) can be served as a suitable analogue 17,31 to PuSiO 4 due to the inherent challenges associated with handling radioactive plutonium and synthetic challenges to acquire pure phase of PuSiO 4 , as cerium carries both +3 and +4 charges and exhibits similar ionic radii to plutonium, allows for more manageable experimentation. 32–35 In situ high-pressure Raman spectroscopy experiments and synchrotron X-ray diffraction have revealed that phase transition of stetindite differs from coffinite.…”