Calcium, Lanthanide, and Zirconium Vanadates with the Zircon Structure: Preparation, Structure, and Behavior during Heating

— Using coprecipitation, we have synthesized LnVO 4 (simple) and CaLnZr(VO 4 ) 3 (Ln = Nd, Sm, Eu, Gd, Dy, Yb) (ternary) lanthanide orthovanadates; a La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 VO 4 solid solution, modeling the composition of the lanthanides in radioactive waste (all crystallizing in the zircon structure, sp. gr. I 4 1 / amd ); and LaVO 4 , crystallizing in the monazite structure. Their unit-cell parameters have been shown to increase systematically with increasing lanthanide ionic radius. Their mid- and far-IR vibrational spectra suggest that their symmetry is lower than that of classical zircon. The synthesized compounds are stable up to 900°C. Their average thermal expansion coefficients lie in the range (6–11) × 10 –6 K –1 .