P. Wodniecki

Oxygen stabilized radiation damage in α-irradiated silver and silver indium alloys

Abstract The annealing behaviour of radiation damage in internally oxidized silver and dilute AgIn alloys was investigated by the TDPAC technique and the reaction 109 Ag(α,2n) 111 In. In the temperature range from 470 to 770 K, three sharp quadrupole frequencies were observed, if oxygen had been introduced into the foils before irradiation, and attributed to the formation and disintegration of defect clusters containing 111 In, oxygen and vacancies. This stabilisation effect of radiation damage was studied as function of the In and O concentration in the sample.

Oxygen agglomeration at111In in silver in the presence of radiation defects

The internal oxidation process of111In in Ag has been studied by means of the perturbed angular correlation technique. A homogeneous111In concentration of typically 0.05 at ppm has been produced by irradiating the Ag samples with 35 MeV α-particles. In particular, the effects of solving oxygen before the irradiation and of radiation induced defects have been explored. It is found that oxygen stabilizes the radiation damage by several hundred degrees. Four molecule-type complexes have been identified, consisting each of one111In atom, vacancies and oxygen atoms, among them one with cubic environment υQ=0. The formation and desintegration kinetics of these complexes have been studied as function of the oxygen concentration and the irradiation and measuring temperature. A model is suggested which explains the oxidation process as due to diffusing oxygen and oxygen-vacancy pairs trapped by111In.

The hafnium aluminides HfAl3 and Hf2Al3 studied by perturbed angular correlations with 181Ta and 111Cd probes

Abstract The electric quadrupole hyperfine interactions for 181 Hf/ 181 Ta and 111 In/ 111 Cd probes in the polycrystalline hafnium aluminides HfAl 3 and Hf 2 Al 3 were measured in the temperature range 30–1100 K. On the basis of the similarities of the numbers, sizes and asymmetries of electric field gradients, lattice site allocations were made. In all matrices, 181 Hf/ 181 Ta was found to substitute into the Hf site. The 111 In/ 111 Cd impurities were also assigned to the Hf lattice site in the low-temperature phase of HfAl 3 , which has D0 23 structure, but appear to substitute into the two non-equivalent Al sites in the Hf 2 Al 3 phase, which has Fdd2 crystallographic structure.

Hf and Zr aluminides with Bf-type structure studied by PAC with 181Ta and 111Cd probes

The hyperfine quadrupole interaction parameters and their temperature dependences for 181Hf/181Ta and for 111In/111Cd probes in the polycrystalline HfAl and ZrAl isostructural compounds were determined. Strong preference of 111In solute for the Zr2Al3 phase occurring as a contamination fraction in ZrAl sample was observed.

PAC studies on xenon irradiated Ti and Ni films and Ni-Ti multilayers

Abstract The perturbed angular correlation (PAC) method was applied to investigate the effects of irradiating Ni and Ti films as well as Ni-Ti bilayers and multilayers with 900 keV Xe2+ ions. The ≈ 200 nm thick layers were deposited onto Si substrates by electron gun evaporation in an UHV chamber. Some 1012 radioactive 111In ions were implanted at 400 keV. The PAC spectra of the Ni-and Ti-films measured at room temperature exhibit the known magnetic and electric hyperfine frequencies ωL = 95.7 MHz (Ni) and νQ = 27.3 MHz (Ti) typical for substitutional implantation. Xe-irradiations up to 2 × 1016 cm−2 did not change these parameters, but slightly increased the distribution widths. When irradiating Ni-Ti multilayers, amorphization was observed at a Xe-fluence of about 1015 cm−2. In addition, the RT mixing rate in Ti-Ni bilayers was measured via Rutherford backscattering.

The HfAl2 and ZrAl2 Laves phases studied by 181Ta and 111Cd perturbed angular correlation spectroscopy

Abstract Using perturbed angular correlation (PAC) spectroscopy and 181 Hf/ 181 Ta and 111 In/ 111 Cd radioactive probes, the electric field gradients (EFGs) in the ZrAl 2 and HfAl 2 Laves phases were measured in the temperature range 20–1100 K. In both matrices, 181 Hf was found to substitute at the unique Hf/Zr site. In the ZrAl 2 compound, the 111 In probes were assigned to the two Al sites. The relative fractions of the corresponding EFGs indicate a strong preference of these impurities in favor of the 2( a ) Al site over the 6( h ) Al site. In the HfAl 2 compound, the 111 In impurities substitute for Hf up to 370 K and reach the Al sites only above 420 K. In both compounds and for both radioactive probes, the temperature dependence of the quadrupole interaction frequencies was measured. It is interesting to note that, for 181 Ta in both compounds, they increase with temperature.

Hyperfine interaction of 111Cd in Fe–Sn compounds

The hyperfine interaction of 111Cd in ferromagnetic Fe3Sn compound was investigated by TDPAC in the paramagnetic region and below the Curie temperature. The results are compared with hyperfine magnetic fields and EFGs on 111Cd and 119Sn in other stoichiometric Fe–Sn phases.

The Zr2Al and Zr3Al compounds studied by PAC with 181Ta and 111Cd probes

Abstract The perturbed angular correlation technique was applied to study the electric field gradients of 111 In/ 111 Cd and 181 Hf/ 181 Ta radioactive probe atoms in the compounds Zr 2 Al and Zr 3 Al. In both matrices 181 Hf/ 181 Ta was found to substitute into the Zr sites. The 111 In/ 111 Cd probes were assigned to the unique Al site in the Zr 2 Al compound, while in the Zr 3 Al compound they were distributed between the unique Zr and Al positions of this lattice, with a clear preference for the Al site. The temperature dependences of the various quadrupole frequencies were measured in the temperature range from 20 to 1100 K.

Isothermal annealing of oxygen decorated defects in silver

The dynamics of trapping and detrapping processes of oxygen decorated radiation defects in silver were investigated by the TDPAC technique. Three defect clusters containing In, oxygen and vacancies were studied by isothermal annelaing experiments between 250°C and 450°C. For the desintegration respective formation of two of these complexes, activation energies of Ea=1.02±0.08 eV and Ea=0.94±0.12 eV were found.

Structural characterization of the Zr4Al3 and Hf4Al3 compounds by means of hyperfine interaction studies

Electric-field gradients have been measured in the isostructural intermetallic compounds Zr4Al3 and Hf4Al3, using radioactive 181Hf/181Ta hyperfine probes. In both compounds, two well-defined electric-field gradients have been observed, whose temperature dependence follows the T3/2 rule in the temperature range 30?1170?K. Using the full-potential augmented plane-wave + local-orbitals formalism, the electric-field gradients have been calculated. On the basis of the 181Ta hyperfine interaction parameters, the possible Hf/Zr lattice sites have been assigned. In this way the controversy concerning the lattice structure of these compounds deduced from X-ray diffraction has been solved.