Lattice enthalpies, polarizabilities and shear moduli of lanthanide orthophosphates LnPO4.

Lattice energies ΔLHθ of lanthanide orthophosphates, LnPO4 (Ln=Ce-Lu, excluding Pm) have been determined from the Born-Haber cycle and compared with those calculated by other methods. The Born-Haber cycle results in close values of ΔLHθ to those obtained after an empirical equation proposed by Glasser and Jenkins. It has been found that: (i) the partial derivative of the lattice enthalpies to the molar volumes corresponds by dimension and magnitude to the shear moduli of these crystals; (ii) these moduli differ for the monazite- and xenotime-type structures of LnPO4. Molar polarizabilities have been calculated for three LnPO4 with monazite structure, Ln=Ce, Nd, Sm, and for three LnPO4 with xenotime structure, Ln=Tb, Dy, Yb.