X-ray diffraction study on thermal properties of crystal lattices in CeP and CeAs

X-ray diffraction studies at low temperatures have been performed in order to investigate thermal properties of crystal lattices in the low-carrier-density systems cerium monopnictides. CeP and CeAs show large crystal-lattice contractions with increasing temperatures up to about 120 K and 90 K, respectively. Due to the strong p-f mixing, the excited crystal field Γ₈-like state is expected to produce a shorter interatomic bond length between cerium ions and neighboring pnictogens than that realized by the Γ₇ ground state. The experimental results of the lattice contractions at low temperatures are explained by the thermal average of these crystal field states.