Schottky contribution to the heat capacity of monazite type (La, Pr)PO4 from low temperature calorimetry and fluorescence measurements

Abstract

We show that the combination of fluorescence spectroscopy and low temperature heat capacity measurements of Pr-containing samples in the (La,Pr)PO4 solid solution series can be employed to strongly constrain the Stark energy levels of Pr3+ in monazite type structures. The resulting set of Stark energy levels for the 3H4 ground state of Pr3+ reproduces the low temperature Schottky anomaly of the heat capacity much more accurately than theoretical models published earlier. We also show that there is no excess heat capacity along the binary solid solution with respect to an interpolation between the two end members LaPO4 and PrPO4.