Extracting structural information from low symmetry crystal field parameters-case study: Er3+ and Nd3+ ions in YAlO3

The experimental monoclinic CF parameter (CFP) sets obtained by Duan et al. (Phys. Rev. B 75 (2007) 195130) for Er3+ and Nd3+ ions in YAlO3 were reanalyzed. These CFPs fitted using R-approach, i.e. with the monoclinic second-rank CFP set to zero, and additionally with one six-rank CFP fixed to zero, turned out to be non-standard. In order to understand better the low symmetry aspects involved in the fitted CFPs and extract useful structural information inherent in monoclinic CFPs, an approach comprising four methods was utilized. First, superposition model (SPM) was applied to calculate CFPs in the crystallographic axis system. Second, the principal values for the SPM determined CFPs and the orientation of the principal axis system w.r.t. the crystallographic axis system were obtained using the procedure 3DD for diagonalization of the 2nd-rank CFPs. Third, analysis of higher symmetry approximations, i.e. orthorhombic and tetragonal, was carried out using the pseudosymmetry axes method. Fourth, the closeness factors and norm ratios were employed for quantitative comparisons of various CFP sets. Partial results for Er3+ ions in YAlO3 were presented here, whereas detailed results would be given in a follow-up paper.