P. Wodniecki’s research while affiliated with Institute of Nuclear Physics, Polish Academy of Sciences and other places

The hyperfine quadrupole interaction of 181Ta and 111Cd probes in HfAg and Hf2Ag compounds was studied at 24 to 1100 K with the time -differential perturbed angular correlation (TDPAC) technique. The EFGs measured in HfAg on 181Ta and 111Cd are 1.388(5)×1018 Vcm-2 and 0.340(5)×1018 Vcm-2, respectively. For both probe atoms a linear decrease of the EFG with temperature was observed with slopes 1.11(2)×10-4 K-1 and 1.73(5)×10-4 K-1 for 181Ta and 111Cd, respectively. In Hf2Ag, 0.469(2)×1018 Vcm-2 was determined on 181Ta nuclei and 0.428(5)×1018 Vcm-2 on 111Cd. Also a linear EFG temperature dependence with the large slope of 2.39(6)×10-4 K-1 was observed for 111Cd probes in Hf2Ag, while the EFG measured on 181Ta nuclei in this compound exhibits a very weak temperature variation which can be fitted neither with a linear T nor a T3/2 dependence. In all cases the electronic contributions to the EFG are very small indicating that these transition element systems do not obey the universal correlation between the electronic and the ionic EFG observed in numerous other systems not belonging to the transition metal series.

The quadrupole interaction in Au-In compounds of different stoichiometrics was studied with the perturbed angular correlation technique. The electric field gradients at

The quadrupole interaction of 181Ta probes in isostructural Cu8Hf3 and Cu8Zr3 intermetallic compounds was studied in the temperature range 24 K-1100 K with the time-differential perturbed angular correlation technique. Two nonaxial electric field gradients corresponding to two nonequivalent hafnium or zirconium sites in the investigated structure were found. A linear decrease in the quadrupole interaction frequency with increase of temperature for the 8(d) sites was evidenced, while the vQ(T) dependence for the 4

Perturbed angular correlation (PAC) method was applied to study the martensitic phase transition of the TiPd shape memory alloy doped with In, Hf, and Zr. The hyperfine interaction parameters and their concentration and temperature dependences for 111In/111Cd and 181Hf/181Ta probe atoms were determined. The influence of ternary element additions on the electric field gradients at Pd site was evidenced. A decrease of the martensite start temperature (MS) and an increase of the width of the hysteresis loop (TH) with an increasing concentration of the impurities in TiPd alloy was observed. These relationships are much stronger for In and Zr, than for Hf admixture.

The quadrupolar hyperfine interactions of in-diffused (111)In --> (111)Cd probes in polycrystalline isostructural Zr(4)Al(3) and Hf(4)Al(3) samples containing small admixtures of the phases (Zr/Hf)(3)Al(2) were investigated. A strong preference of (111)In solutes for the contaminant (Zr/Hf)(3)Al(2) minority phases was observed. Detailed calculations of the electric field gradient (EFG) at the Cd nucleus using the full-potential augmented plane wave + local orbital formalism allowed us to assign the observed EFG fractions to the various lattice sites in the (Zr/Hf)(3)Al(2) compounds and to understand the preferential site occupation of the minority phases by the (111)In atoms. The effects of the size of the supercell and relaxation around the oversized In and Cd probe atoms were investigated in detail.

Perturbed angular correlation (PAC) method was applied to study the electric field gradients in nanopowders of the HfAl2 and HfAl3 intermetallic compounds, obtained via mechanical alloying or after ball milling of the thermally alloyed compound. The influence of the ball milling procedure on the experimentally obtained hyperfine interaction parameters was determined. A strong dependence of the PAC pattern on the milling time was evidenced and attributed to the structural disorder. The thickness of the outer damaged part of the grains depends on the crystallographic structure of the milled material. In HfAl3 sample the influence of the milling procedure on the phase transformation was observed.

Perturbed angular correlation (PAC) method was applied to study the martensitic phase transition of the TiPd shape memory alloy doped with 111In/111Cd probe atoms. The hyperfine interaction parameters and their concentration and temperature dependences for probes with cubic and noncubic surroundings of the lattice sites, consistent with the respective crystal structures in martensite and austenite phase, were determined. A strong dependence of the martensite start temperature (MS) and shape of the hysteresis loop (TH) on the small admixture of the In impurities in TiPd compound was evidenced. The observed decrease in the MS depends not only on the amount of the third element, but also on the element itself. The data were compared with those obtained with 181Hf/181Ta probes in TiPd alloy with hafnium admixture.

The hyperfine quadrupole interaction parameters and their temperature dependence for 181Hf/181Ta probe in TiAl3 compound were determined using the time differential perturbed angular correlation (TDPAC) method. In addition, ab initio calculations using the augmented plane wave plus local orbitals (APW + lo) method as implemented in the WIEN2k code, within the framework of the density functional theory (DFT) have been performed. Through the comparison of the calculated and measured electric field gradients (EFG) it was established that Ta occupies Ti 2(a) position, while Cd probe is settled at the Al 4(d) site.

The hyperfine quadrupole interaction parameters and their temperature dependences for 181Ta and 111Cd probes in Ti2Pd compound were determined experimentally by means of the perturbed angular correlation (PAC) technique. In addition, ab initio calculations using all-electron augmented plane wave plus local orbitals (APW + lo) method have been performed. Through the comparison of the calculated and measured electric field gradients (EFG) it was established that both Ta and Cd occupy 4(e) Ti position in the Ti2Pd compound.

By using the time-differential perturbed angular correlation technique, the electric field gradients (EFG) at (181)Hf/(181)Ta and (111)In/(111)Cd probe sites in the MoSi(2)-type compound Ti(2)Ag have been measured as a function of temperature in the range from 24 to 1073 K. Ab initio EFG calculations have been performed within the framework of density functional theory using the full-potential augmented plane wave+local orbitals method as implemented in the WIEN2k package. These calculations allowed assignments of the probe lattice sites. For Ta, a single well-defined EFG with very weak temperature dependence was established and attributed to the [4(e)4mm] Ti site. For (111)Cd probes, two of the three measured EFGs are well defined and correlated with substitutional lattice sites, i.e. both the [4(e)4mm] Ti site and the [2(a)4/mmm] Ag site.