NUCLEAR ^{\scriptstyle111} Cd PROBES DETECT A HIDDEN SYMMETRY CHANGE UNDER THE γ \rightarrow α TRANSITION IN CERIUM CONSIDERED ISOSTRUCTURAL FOR 60 YEARS
Tsvyashchenko A.V., Nikolaev A.V., Velichkov A.I., Salamatin A.V., Fomicheva L.N., Ryasny G.K., Sorokin A.A., Kochetov O.I., Budzynski M.

Received: March 5, 2010

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We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions of probe ¹¹¹ Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known phase transition in cerium is not isostructural. In α- Ce, the probe ¹¹¹ Cd 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 Ref. [14]. We relate our findings to the current understanding of the 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).