Electric Quadrupole Interaction of181Ta Research Articles

Perturbed angular correlation studies of 181Ta hyperfine interactions in Hf–Ni and Zr–Ni compounds

The hyperfine interaction experienced by 181Ta nuclei in the intermetallic compounds ZrNi 5, HfNi 5, and Hf 2Ni 7 has been investigated by perturbed angular correlation (PAC) spectroscopy. At temperatures T≥15 K the 181Ta angular correlation of appropriately annealed ZrNi 5 and HfNi 5 is unperturbed, indicating the absence of a magnetic hyperfine interaction. This observation rules out the possibility of spontaneous magnetic order of ZrNi 5 and HfNi 5 recently proposed in the literature. The temperature dependence of the electric quadrupole interaction of 181Ta in Hf 2Ni 7 suggests the existence of a reversible phase transformation at T≥500 K.

Hyperfine spectroscopic study of Hf2Fe hydrides and their thermal stability

Perturbed angular correlation (PAC) spectroscopy has been used to investigate the hydrides of the intermetallic compound Hf2Fe. Aiming at information on the hydrogen diffusion, measurements of the electric quadrupole interaction of 181Ta on Hf sites of Hf2FeHx have been carried out in the concentration range 0.8≤x≤4.8. PAC measurements as a function of temperature show that for hydrogen concentrations x>1.5 these hydrides are thermally unstable and decompose at T≈650 K. The time constant of the decomposition at 1100 K was determined by PAC spectroscopy to be τ=1.0(2) h for x=3.75. The cubic Hf hydride δ-HfHx with x≈1.6 and the intermetallic compound HfFe2 were identified as well crystallized segregation products by X-ray diffraction and 57Fe Moessbauer spectroscopy. The activation energy for hydrogen jumps in the decomposition product δ-HfHx was determined to be Ea = 0.50(3) eV. The thermal stability increases towards lower hydrogen concentrations. For x≤1 the PAC spectra of Hf2FeHx were found to be fully reversible between 290 K and 1100 K. Hf2FeHx has been reported to show magnetic order at large hydrogen concentrations and low temperatures. PAC measurements for large x values and temperatures between 290 K and 9 K, however, gave no evidence for a magnetic hyperfine field at the Hf sites. Moessbauer measurements suggest that the magnetic order temperature of Hf2FeH3.9 is less than 50 K.

Pac studies of the electric quadrupole interaction of181Ta in yttrium and copper oxides and in super conducting ceramics YBa2Cu3O7−δ

The electric quadrupole interaction of181Ta in Y2O3, CuO, and in the YBa2Cu3O7−δ high temperature superconductors, doped with181Hf, has been studied by the time-differential perturbed angular correlation method (TDPAC). In Y2O3, two distinct fractions of the probe nuclei were detected, which were attributed to the substitutional positions at the two cation sites in the lattice. In CuO, and in the ceramic samples, broad distributions of quadrupole frequencies were observed. Possible configurations of the probe nuclei in these substances are discussed.

Electric quadrupole interaction of181Ta in Pd and Zn

A strong electric field gradient (EFG) has been observed at181 Ta in Pd and Zn metals using DPAC technique. The value of the EFG in Pd is found to be 12.5(8)×1017 V/cm2 with an asymmetry parameter (η) of 0.33(2). The value of the EFG in Zn has the same value as in the Pd metal, but the asymmetry parameter has the value 0.36(3). The variation of EFG in Pd with temperature has shown a weak dependence. The results are interpreted in terms of oxygen trapping at Hf atoms during the sample preparation.

The electric quadrupole interaction of181Ta in the Hf−As system

The temperature dependence of the electric quadrupole interaction of181Ta in the Hf−As system has been investigated using the time-differential perturbed angular correlation technique. The sample was prepared by thermal diffusion of181Hf into arsenic metal and the measurements were made at 77, 300, 423, 573 and 673 K. Two quadrupole interaction frequencies were observed which had considerably high values and showed little variation over the entire temperature range. A TEM analysis of the sample showed the presence of two intermetallic compounds HfAs and HfAs2 to which the two frequencies were assigned.

Temperature dependence of electric quadrupole interaction of181Ta in HfO2

High-resolution TDPAC determination of EQI of181Ta in HfO2 is performed. Room temperature parameters of ωQ = 111 (1) MHz and η=0.36(1) are obtained. The temperature dependence of ωQ and η in the range 78–1100 K is established. An explanation of the observed phenomena in a dielectric lattice is discussed.

Study of the static electric quadrupole interaction of181Ta nuclei in HFO2

Study of the static electric quadrupole interaction of181Ta nuclei in HFO2

Kinetics of lithium intercalation into 2H-TaS 2

Perturbed angular correlation measurements of the evolution in time of the electric quadrupole interaction of 181Ta in 2H-TaS 2 reacting with excess n-butyl-lithium show that the Li intercalation proceeds via two discrete ordered intermediate steps.

Quadrupole Interaction in Hafnium Metal

The electric quadrupole interaction of 181Ta in Hf metal has been measured as a function of the annealing temperatures of the irradiated samples. The asymmetry parameter obtained was η = 0.3, independent of the thermal history of the samples.

Quadrupole Interaction of 181Ta in Hafnium Oxychloride

The static electric quadrupole interaction of 181Ta in HfOCl2∙8H2O and HfOCl2∙4H2O, incorporating the perturbed angular correlation of the 133–482 keV γ-rays cascade, has been measured. The quadrupole interaction frequencies obtained were ω1 = (1356 ± 65) mrad/s for HfOCl2∙8H2O, and ω1 = (858 ± 40) mrad/s, η = 0.58 ± 0.01 for HfOCl2∙4H2O. Comparison with other measurements is given.

Static electric quadrupole interaction of Ta- and Hf-ions in barium and lead titanate

The static electric quadrupole interaction of181Ta and178Hf in polycrystalline barium and lead titanate at the site of titanium has been measured using time differential PAC and the Mossbauer effect.

Electric quadrupole interaction of 181Ta in hexagonal transition metals

Abstract The electric quadrupole interaction of 181Ta impurity atoms in the hexagonal transition metals Re, Os, Hf and Ru has been studied at room temperature. From the resolved Mossbauer absorption spectra values for the electric field gradients at the 181Ta nucleus and for the isomer shifts of the 6.2 keV gamma rays were obtained.

Quadrupole interaction of 181 Ta in Hf compounds

Time-differential angular correlation studies of the electric quadrupole interaction of 181 Ta in various Hf compounds are presented. Methods for the analysis of the time spectra are discussed. The experiments yield information on the strength of the quadrupole interaction, and on the axial asymmetry and distribution of the field gradient. Electric field gradients V zz are derived for 181 Ta in Hf metal, HfO 2 , and (NH 4 ) 2 HfF 6 .