Interconfiguration fluctuation of cerium in CeN as a function of temperature and pressure

The lattice parameters of the cubic (NaCl-type) compounds LaN, CeN, NdN and ErN were determined in the 77-800K temperature range at normal pressure, and between 1 atm and 80 kbar at room temperature. The analysis of the crystallographic data allows us to conclude that La, Nd and Er are trivalent in their nitrides, whereas Ce in CeN shows, under every examined condition, an ionic radius lower than that expected for Ce 3+ , indicating the possible occurrence of interconfiguration fluctuations between the Ce 3+ and Ce 4+ states. The average valency of Ce in CeN appears to be 3.85 under standard conditions and its dependence upon the thermodynamic parameters (T,P) was determined; the results indicate that the valency value increases continuously when the temperature decreases or the pressure increases, rising to 3.89 at 100K, 1 atm and to 3.94 at 298K, 50 kbar.