The time-differential perturbed angular correlations technique (TDPAC) has been employed for measuring the parameters of hyperfine interactions in earlier known RAl3 compounds, synthesized at high pressure (8 GPa) and high temperature, where R = La, Ce, Sm, Gd, Th, Dy, Ho, Er, Yb and Lu. The Cd-111(In-111) radioactive atom was used as a probe nucleus. The X-ray method has revealed that with the increase in the atomic number of a rare-earth element R, the obtained RA13 high-pressure phases crystallize, respectively, into orthorhombic, hexagonal and cubic structures. It has been found that in the compounds containing R = La, Ce, Sm and Gd, a deviation from earlier known structural types and the formation of new ones is observed, which is associated with the change of the stoichiometric composition of the said compounds. The results of the PAC measurements have confirmed the deviation from the predetermined stoichiometric composition 1R:3Al for the compounds LaAl3, CeAl3, SmAl3 and GdAl3 and have verified the RAl3 stoichiometric structure for the other high-pressure phases obtained in this work. (c) 2007 Elsevier Ltd. All rights reserved.

The quadrupole interaction at 111Cd impurity nuclei in the intermediate-valence compound YbAl2 has been measured under pressure up to 80 kbar by the TDPAC spectroscopy. It was found that the quadrupole frequency nQ measured on the 111Cd located at the Al sites in YbAl2, varies nonlinearly and increases by almost four times with the pressure increase up to 80 kbar. A linear correlation between the mean Yb valence, derived from Yb L3 OFY-XAS and RXES measurements, and the electric field gradient (the quadrupole frequency nQ=eQVzz/h) has been observed. The quadrupole frequencies on 111Cd in the GdAl2, YbAl3, TmAl3 and CaAl2 compounds have been measured, also. The possibility of determining the valence of Yb in the Yb compounds with p-metals from the relation nQ (u(P)) = n2 + (n3 - n2) u(P) has been considered.

The quadrupole interaction at Cd-111 impurity nuclei in the intermediate-valence compound YbAl2 has been measured under pressure up to 80 kbar by the time-differential perturbed angular correlation spectroscopy. It was found that the quadrupole frequency nu(Q) measured on the Cd-111 nuclei located at the Al sites in YbAl2 varies nonlinearly and increases by almost four times with the pressure increase up to 80 kbar. A linear correlation between the mean Yb valence, derived from Yb L-3 OFY-XAS and RXES measurements, and the electric field gradient (the quadrupole frequency nu(Q)=eQV(zz)/h) has been observed. The quadrupole frequencies on Cd-111 in the GdAl2, YbAl3, TmAl3, and CaAl2 compounds have been also measured. The possibility of determining the valence of Yb in the Yb compounds with p metals from the relation nu(Q)(upsilon(P))=nu(2)+(nu(3)-nu(2))upsilon(P) has been considered.

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.

The perturbed angular correlation (PAC) measurements with the 111In-111Cd nuclear probe embedded into the lattice of the cubic (C15) Laves compound ZrZn2 showed that 111Cd nuclei experienced an axially symmetric electric quadrupole interaction with a frequency ν Q  = 132.4 MHz at room temperature. The samples were synthesized and doped with the probe at a pressure 8 GPa. The temperature dependence of ν Q was shown to be linear: ν Q (T) = 147(1 − 0.033 T) MHz. Since the value of ν Q is very close to that known for 111Cd in the lattice of Zn, we have checked if it could be assigned to residual Zn metal in the sample. For the Zn sample melted and doped with 111In at 8 GPa we have obtained ν Q  = 117.3 MHz at 300 K and 127 MHz at 80 K – both values considerably lower than that for 111In doped Zn samples prepared at an ambient pressure. These data, and the fact that ν Q (T) in Zn is known to follow the T 3/2 law, allow to attribute the ν Q value quoted above to 111Cd nuclei at the substitutional sites with tetrahedral symmetry in the Zn sublattice of ZrZn2.

Quasibinary Laves systems (Ce1−xLax)Ru2 and (Ce1−yCay)Ru2 doped with 111In were synthesized at a pressure of 8GPa, and variations of the electric quadrupole interaction of 111Cd at the Ru sites have been studied by the method of time-differential perturbed angular correlation in a wide range of Ce–La and Ce–Ca relative concentrations. In the first case two sites with quadrupole frequencies νQ≅220 and 150MHz persist at x≤0.2, while at x≥0.3 only the higher frequency component remains in the spectra, which are similar to that of pure LaRu2. In the series (Ce1−yCay)Ru2, at y≥0.03 the lower frequency component was washed out except in samples with y=0.1 and 0.2, where it was restored.