A Time-Differential Perturbed Angular Correlation Study of K₃HfF₇

Abstract

<p>The method of using time dependent perturbed angular correlations (TDPAC) is used in a study of the hafnium atom's environment in K₃HfF₇. It is found that there are two possible electric field gradients (EFG), different in both magnitude and, asymmetry about the axis of the greatest component, at sample temperatures below 250 ± 1 Kelvin and only one above. This indicates that a solid to solid phase transition occurs at this temperature from a two site structure for the hafnium to a one site form. The EFG asymmetry of the low temperature site, having a relative population of 0.25, increases from 0.62 ± .0.3 to >.95 between 170 and 230 Kelvin. This can be interpreted as the effect of a second state of this hafnium site with an energy difference of approximately 0.25 eV and a relative degeneracy of approximately 10⁻⁷. Such a state could be the result of an impurity or lattice distortion.</p> <p>Using the K₃HfF₇ as a sample study, the observed data was operated on in a deconvolution analysis to remove the effect of the finite time response of the measurement apparatus. An iterative Bayesian approach was found to amplify high frequency spectral noise less than the linear inverse filter technique however the noise inherent in the measured data limits the usefulness of this type of analysis. The parameters used to describe the EFG interaction, evaluated in a least squares fit of the theoretical expression to the data, were found to be unaffected by the deconvolution operation within statistical uncertainties.</p>