Samples of BaHf03 were irradiated with fast and thermal neutrons to produce ' 'Hf. Attenuations of the y-y perturbed angular correlations in '"Ta were observed, and they may have been caused by the interaction between defects (produced during or after neutron irradiation} and oxygen vacancies. Several defect structures were detected. For one of the structures, an excitation energy of 12 meV was measured, which was attributed to an electron state below the conduction band. The values of the dielectric constant and of the effective electron mass were also deduced.
We report on a time differential perturbed angular correlations (TDPAC) study of the hyperfine interactions at lxl Ta in Hf 2 Ni 7 and Zr 2 Ni 7 . The samples were prepared by arc melting proper amounts of constituents together with a small amount of Hf containing radioactive 18 'Hf atoms. A further heat treatment was necessary to obtain samples of the required crystal structure (monoclinic symmetry in the C2/m space group). As known, two non-equivalent lattice sites of Hf/Zr metal exist in this structure.The PAC measurements were performed at 20 -1123 K. Two quadrupole interactions were observed, corresponding to two possible crystallographic positions of the probe atom in the studied structure. The electric quadrupole interaction parameters at 18 'Ta in Hf 2 Ni 7 are ^Q 1 (300K) = 586.7(65) MHz with r/, = 0.79 (4) and j/ Q2 (300K) = 466.8(41) MHz with r? 2 = 0.20(3), and in Zr 2 Ni 7 they are I/ Q1 (300K) = 498.4(22) MHz with 77, = 1.0 and u Q2 (300K) = 418.0(50) MHz with 77 2 = 0.35(3). The presence of a magnetic interaction, reported in the literature, was not confirmed.
The perturbed angular correlation (PAC) technique was applied to study the electric field gradients at 111 In sites in CdIn 2 O 4 . The measurements were carried out at temperatures in the range 150Y1073 K. The aims of the study were both to characterize the quadrupole interactions of the tracers and to determine the distribution of indium ions among the available sites in the spinel structure. Room temperature measurements corresponding to samples cooled at different rates are also reported.
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