Reinterpretation of crystal field parameters for rare-earth nickelates RNiO3 (R=Pr, Nd, Sm, Eu, and Pr1−xLax, 0⩽x⩽0.7)

A major goal of this paper is to propose the general method of crystal field (CF) analysis for low symmetry cases. A literature survey indicates that some authors are still unaware of the standardization idea, whereas often no clear definitions of the axis system used for a given ion/host are provided. An illustrative example of such cases is provided by the crystal field parameter (CFP) datasets for the rare-earth nickelates RNiO3 (R=Pr, Nd, Sm, Eu, and Pr1−xLax, 0⩽x⩽0.7) available in literature. To meaningfully compare disparate CFP datasets for the same or similar ion/host systems, which may be likely expressed in different axis systems, standardization of the non-standard CFPs must be carried out. The standardized CFPs as well as related conserved quantities are calculated and reanalyzed for these nickelates compounds. The extended computer package CST (Conversions, Standardization, and Transformations) is used to achieve the standardization of the CFP datasets. A detailed discussion of the axis systems and the related aspects concerning the independent CF parameters for monoclinic symmetry is presented.