Compressibility and structural stability of CeN from experiment and theory. The B1–B2 transition

The high-pressure structural stability of CeN is investigated by experiment and theory. Experiments are carried out by energy-dispersive X-ray diffraction and synchrotron radiation, using a diamond anvil cell, to a maximum pressure of 77 GPa. The experimental results are in remarkably good agreement with ab initio calculations using the full-potential linear muffin-tin orbital method within the generalized gradient approximation (GGA). The experimental zero pressure bulk modulus is B0 = 156(3) GPa, the pressure derivative being constrained to B0′ = 4.00. The corresponding calculated data are B0 = 158.1 GPa and B0′ = 3.3. We report here the first experimental observation of the transformation of CeN from the ambient B1 type crystal structure to the B2 type. The onset of the transition is in the range 65–70 GPa, and the relative volume change at the transition is ΔV/V = −10.9(3)%. These data compare well with the calculated transition pressure Ptr = 68 GPa and ΔV/V = −10.8%. Experimentally, the transition is found to be rather sluggish.

► First experimental determination of bulk modulus of CeN.
► First observation of B1–B2 transformation in CeN.
► Density functional calculations in remarkably good agreement with experiment.
► Calculations extended to B2 phase, including B1–B2 transition.