O.I. Kochetov

Nuclear 111Cd probes detect a hidden symmetry change at the γ → α transition in cerium considered isostructural for 60 years

We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions of probe 111Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known γ → α phase transition in cerium is not isostructural. In α-Ce, the probe 111Cd nuclei reveal a quadrupole electron charge density component that is absent in γ-Ce. The hidden spacial structure of electronic quadrupoles in α-Ce is triple-q antiferroquadrupolar, as was suggested in [14]. We relate our findings to the current understanding of the γ → α phase transition and also report on nuclear quadrupole interactions in other high-pressure phases of cerium: α″ (C2/m space symmetry) and α′ (α-U structure).

Investigation of hyperfine quadrupole interactions in UGe2 and UAl2 compounds on 111Cd probe nuclei by the perturbed angular correlation method

The parameters of nuclear quadrupole hyperfine interaction in intermetallic UGe2 and UAl2 compounds have been measured in a temperature range of 100–300 K using the perturbed angular γγ correlation method on 111Cd probe nuclei. The results obtained for UGe2 indicate a pronounced anisotropic character in the distribution of f electrons in agreement with the calculation of the electronic structure of this compound. The hybridization degree between f electrons of U and p electrons of Al in UAl2 is lower than the hybridization degree between f electrons of U and p electrons of Ge in UGe2.

Study of the electric field gradient at 111Cd in the RAl3 compounds synthesized under high pressure

The electric quadrupole interaction parameters for impurity 111Cd nuclei in intermetallic RAl3 compounds (R = La, Ce, Sm, Gd, Tb, Dy, Ho, Er, Yb, or Lu) synthesized under high (8 GPa) pressure at high (1800–1900°C) temperatures have been measured using the method of perturbed angular γγ correlations. It has been established by X-ray diffraction analysis that with an increase in the atomic number of the R element the obtained high-pressure phases are crystallized successively in the orthorhombic, hexagonal, and cubic structures. In the compounds with R = La, Ce, Sm, and Gd, deviation from the known structural types and formation of new ones due to the change in the stoichiometric composition have been observed. The data obtained by the method of perturbed angular γγ correlations have confirmed deviation from the specified stoichiometric composition 1R: 3Al for the LaAl3, CeAl3, SmAl3, and GdAl3 compounds and verified the correctness of the stoichiometric composition and the presence of the Cu3Au structural type for the remaining RAl3 high-pressure phases.

Fluctuating electric field gradients at 111Cd in ice

Abstract111Cd–PAC measurements have been made using the high specific activity of 111In in the methanol–water mixtures of various concentrations at the room temperature. These experiments revealed that the perturbation factors 〈A2G2〉 (integrated over two mean lives τN) do not follow the dependence of the macroscopic viscosity η. The observed dynamic character of the PAC spectra in ice is explained by the mobility of orientational and ionic defects. The activation energy for the diffusion process was determined to be Ea=0.35(1) eV.