Alternative crystal-field parameters for rare-earth ions obtained from various techniques: II. Reanalysis of spectroscopic data for Eu3+ and Er3+ ions in RE2BaXO5 (X = Co, Cu, Ni, Zn) high temperature superconductors and related systems

This is second paper in a series devoted to reanalysis of the non-standard and standard crystal-field (CF) parameter (CFP) sets obtained from various experimental techniques for trivalent rare-earth (RE) ions in high temperature superconductors (HTSC) and related systems. Two intrinsic properties of orthorhombic CF Hamiltonians, not fully recognized in the literature, bear significantly on interpretation of CF data for transition ions. These properties are: (i) existence of alternative (physically equivalent) CF parameter (CFP) sets and (ii) incorrectness of comparison of such alternative yet disparate CFP sets. The orthorhombic CFP sets determined for RE3+ ions in HTSC systems: Eu3+ in Ln2BaZnO5 (Ln = La, Nd, Y) and Eu2BaXO5 (X = Co, Zn) and Er3+ in Y2BaZnO5 and Er2BaXO5 (X = Ni, Cu, Zn) are reanalysed applying standardization and closeness of CFP sets. Correlated CFP sets are transformed to the same nominal standard axis system. Standardization transformations are used to generate alternative (standard and non-standard) CFP sets, which may be utilized in the multiple correlated fitting technique to improve reliability of final fitted CFPs. The discrepancies concerning orthorhombic CFPs, identified in spectroscopic studies under consideration, are clarified. Misinterpretations of CFPs and structural data arising from usage of intrinsically incomparable CFP sets for similar ion-host systems are discussed.