Alternative crystal field parameters for rare-earth ions obtained from various techniques

In this series of papers, implications of two major properties of orthorhombic crystal field (CF) Hamiltonians for interpretation of CF data for rare-earth ions obtained from various experimental techniques are considered. These properties, i.e. existence of alternative (physically equivalent) CF parameter (CFP) sets and incorrectness of comparison of such alternative yet disparate CFP sets, appear not fully utilized in literature. The CFP sets for Tm3+ in orthorhombic high Tc superconductors TmBa2Cu4O8 and TmBa2Cu3O7−δ 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 Mössbauer spectroscopy studies of Tm3+ ion in TmBa2Cu4O8, are clarified. Misinterpretations of CF and structural data arising from usage of intrinsically incomparable CFP sets for similar ion-host systems are discussed.