Approximation of the theory of stochastic perturbations of angular correlations for fluctuating distributions of electric quadrupole interactions

Temperature Dependence of the Hyperfine Interaction at 181Ta in SrHfO3

“…In fact the slow and fast regime occurs from &600 to &850 K (13). The model used to "t the hyper"ne parameters predicts that the activation energies of both regimes should be the same (16,17). The "tted values for the slow and fast regimes are 155 and 177 meV, respectively.…”

Oxidation of Hafnium and Diffusion of Hafnium Atoms in Hexagonal Close-Packed Hafnium; Microscopic Investigations by Perturbed Angular Correlations

“…The activation energy gives the potential energy barrier that an Hf atom encounters when it jumps from an occupied site to a vacant site in the lattice by thermal energy. The quadrupole frequency corresponding to a fluctuating electric field gradient can be determined using the relation λ max 2 (µs −1 ) ≈ 3ω f Q Mrad/s [18]. This has been found to be ≈ 53 Mrad/s for the value of λ max 2 = 160 µs −1 found at a temperature of 573 K. This value of ω f Q matches well with the value of the quadrupole frequency of hcp Hf (∼50 Mrad/s) and supports again that spin relaxations observed at 873 K and lower temperatures are due to fluctuations of Hf atoms.…”

“…The probe 18 Hf nucleus which undergoes β − decay to 181 Ta has been used for present studies. Due to nuclear quadrupole interaction, the 133 -482 keV γ − γ angular correlation of 181 Ta passing through the 482 keV level (Fig.…”

Perturbed Angular Correlation Spectroscopy – A Tool for the Study of Defects and Diffusion at the Atomic Scale

“…Often, empirical expressions for fluctuating HFIs based on the results of Baudry and Boyer [52] and on Forker et al [53] are used when analyzing PAC spectra. At least for "simple" ( ) is the perturbation function that results from the average of attainable HFIs in the motionally averaged limit.…”