Composition, lattice parameters, and room temperature elastic constants of natural single crystal xenotime from Novo Horizonte

The composition, lattice parameters, and elastic constants of natural single crystal YPO₄ xenotime from Novo Horizonte (Brazil) were determined using EPMA, XRD, and the pulse-echo technique. The composition indicates a 24% substitution of Y sites with other rare-earth elements. The lattice parameters of the studied crystal deviated only slightly from those reported for synthetic YPO₄ and were in a good agreement with trends obeyed by other orthophosphates with the xenotime structure. The measured elastic constants C₁₁, C₃₃, C₄₄, and C₆₆ were consistent with synthetic crystals when porosity was accounted for. C₁₂ and C₁₃ constants were evaluated based on the comparison with other materials with xenotime structure. The elastic constants could be rationalized using interionic force constants and bond energies.