Neutron powder investigation of praseodymium and cerium nitride fluoride solid solutions

Abstract

The investigation of CeN x F 3−3 x ( a = 5.8027(2) Å) and PrN x F 3−3 x ( a = 5.7723(1) Å) ( x ⋍ 0.33) solid solutions, using neutron powder diffraction, revealed that nitrogen atoms and fluorine atoms are occupying the tetrahedral holes within the fluorite type structure and that additional fluorine interstitials are observed on positions x, x, x ((32 f) in Fm 3m ) with x = 0.416. Some of the normal fluorite positions in 0.25, 0.25, 0.25 are relaxed on x, x, x ( x = 0.321 for CeN x F 3−3 x and x = 0.331 for PrN x F 3−3 x ) positions but can be considered rather as slightly relaxed normal sites than as true interstitials. The results have been interpreted with [1:0:3] and [1:0:4] defect clusters within these anion-excess-fluorite related structures.