How to analyse powder nuclear quadrupole interaction data with non-axial symmetry for interdependent electric field gradient tensor components

The measurement of nuclear quadrupole interactions from powder (random) samples yields two parameters, namely Vzz and the asymmetry parameter η. Usually, these two parameters are plotted separately versus an external variable. This parametrization is perfectly suited to hide correlations between electric field gradient tensor components, even linear dependences. A new parametrization is proposed that, in the case of linear dependences, consists of a constant scale factor, the ‘asymptotic’ asymmetry parameter, also a constant, and a control parameter that is the only function of an external variable. This parametrization reduces the number of freely adjustable parameters in data fitting by nearly a factor of two. All solid-state effects are contained in a single control parameter. In the case of linear dependences, a two-tiered data analysis is proposed that is compulsory. An extension of the analysis to nonlinear dependences is given as well. The proposed two-tier analysis in the Czjzek plot reveals the structure of the electric field gradient (EFG) tensor. Several examples will be given.

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