Reanalysis of crystal field parameter datasets for rare-earth ions at low symmetry sites: Nd3+ in NdGaO3 and Pr3+ in PrGaO3

This study deals with the compatibility and reliability of the crystal field parameter (CFP) datasets for Nd3+ (Pr3+) ions at low symmetry sites in NdGaO3 (PrGaO3), which exemplify a number of apparently disparate and/or incompatible CFP datasets revealed by our recent literature survey. These considerations clarify three important aspects: (1) the definitions of the axis systems adopted in the pertinent CF studies; (2) the relevant coordination factors involved in the point charge model calculations; and (3) the multiplicative factors missing in some CFP's, e.g., those obtained by inelastic neutron scattering technique. Based on standardization theory, the reanalysis of the CFP's for Nd3+ in NdGaO3 and Pr3+ in PrGaO3 enables to resolve the discrepancies identified in the previous studies. A survey of CFP datasets for Nd3+ ions in other structurally similar crystals is carried out for a meaningful comparison. Correlations between the physically equivalent CFP datasets for Nd3+ ions in NdGaO3 obtained by transformations of the nominal axis system are also considered. This work lays grounds for similar CF studies of rare-earth ions at low symmetry sites.