[en] High T_c superconductivity in the YBaCuO superconductor has been investigated through the quadrupole interaction of the probe nuclei ⁹⁹Tc. The quadrupole interactions were measured by the TDPAC method from 77 to 296 K. The probe nuclei ⁹⁹Tc were introduced into the YBaCuO superconducting specimen by diffusion. The derived electric quadrupole interaction parameters show that the probe nuclei are subject to a unique EFG interaction and occupy a substitutional lattice site in the YBaCuO superconductor. A strong EFG of 10¹⁹ V/cm² was observed. The temperature dependence of the EFG exhibits a linear decrease with temperature increase. Anomalies of both EFG and η were found in the superconducting transition temperature region. The role of the oxygen vacancies in the Cu-O chains is discussed. (orig.)

[en] Moessbauer studies were performed on a 1% by wt. solution of DNF in the liquid crystalline material 40.8, which is a smetic B liquid crystalline material. This sample produced a four-line spectrum. Two peaks showed a larger intensity than the other two. However, the quadrupole splitting between the high-intensity peaks was the same as for the two low-intensity peaks. Other probe molecules in 40.8 have led to a two-line spectrum. Therefore, this leads to the conclusion that the DNF is located at two different sites within the liquid crystal. This four-line spectrum was observed for both the crystal phase and the smetic B glass phase of 40.8. Also, the Debye temperature was measured, together with the order parameter. These results will be discussed. (orig.)

[en] It has been determined that the thermally activated α → β transition occurring in (NH₄)₂HfF₆ at about 370 K is not always reversible. The β-phase hysteresis was investigated between 14 and 400 K. It was possible to explain previously published results without considering the Goldanskii-Karyagin effect. (Auth.)

[en] Published in summary form only

[en] Conversion electron Moessbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the corrosion of the surface of iron foils, which consists of small particles of γ-Fe₂O₃. When the average particle sizes of the corroded layer are approximately 4 and 5 nm, magnetic hyperfine splitting was observed in the spectra at 6.3 and 78 K. However, for a corroded layer composed of smaller particles, the splitting was noticed only at 6.3 K. The anisotropy constant K of the small particles was estimated using the magnetic hyperfine fields obtained from the spectra at 6.3 and 78 K. (orig.)

[en] Moessbauer effect measurements have been made on amorphous Tm_0.41Ag_0.59, using the ¹⁶⁹Tm resonance, over a temperature range of 1.2 K to room temperature. The sample was prepared by sputtering from a composite target. The spectra are very similar to those seen for a-Tm_1-xCu_x. They consist of a magnetically split component and a non-magnetic central doublet. Hyperfine parameter distributions are more consistent with a short range order model than with a dense random packing of ions model

[en] The stochastic theory of Moessbauer line shapes is formulated in a fashion which allows the evaluation of the spectral shapes for absorbers of arbitrary thickness, texture, and an anisotropic Lamb-Moessbauer factor. The results are specialized to a two-state-relaxation model of fluctuating electric hyperfine interaction in the case of an absorber of axially symmetric texture. The formalism is applied to the line shape analysis of Moessbauer spectra of a textured sample of the spin-crossover complex [Fe(mtz)₆](PF₆)₂ (mtz = 1-methyltetrazole). It is found that between 185 and 240 K the rate constants for the HS → LS conversion are temperature independent, whereas an Arrhenius behaviour is found for the LS → HS conversion

[en] We have calculated the Moessbauer absorption integral for symmetrical quadrupole doublets as a function of the effective thickness T of the sample and of the ratio QS/Γ (quadrupole splitting/natural width); the resulting absorption A can be well approximated by a simple expression A∝T/(1+αT), where α is a function of the resolution QS/Γ of the absorption lines. A convenient analytical expression is given for α(QS/Γ). As an example, the thermal variation of the absorption area of a spin cross-over system is analysed. (orig.)

[en] Iron-rich Fe_100-cMn_c-alloys (0< c_Mn<35 at%) are found in three different phase structures depending on manganese concentration: bcc, fcc and hcp. Moessbauer effect studies on these phases reveal different magnetic properties: Ferromagnetism, antiferromagnetism and paramagnetism. The evaluation of poorly resolved Moessbauer spectra of a sample with FeNi-Invar analogous composition (c_Mn=35%) and coexisting fcc and hcp phases was possible with the help of the Alfanas'ev-Tsymbal sharpening method introduced recently. (orig.)

[en] The hyperfine interaction of ¹¹¹Cd probes in preoxidized and α-irradiated Ag_0.94Cd_0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of ¹¹¹Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very similar to the ones observed after α-irradiation. (orig.)