Ivanovski, V.N.; Cekic, B.; Umicevic, A.; Belosevic-Cavor, J.; Schumacher, G.; Koteski, V.; Barudzija, T.: Hf dopands in gamma-prime Ni3Al alloy. Journal of Applied Physics 114 (2013), p. 063712/1-5
10.1063/1.4818317
Abstract:
The Time Differential Perturbed Angular (TDPAC) measurements of nuclear quadrupole interactions (NQIs) at 181Ta ion probe in the polycrystalline intermetallic alloy c0–Ni3Al doped with 0.2 at. % Hf were performed in the temperature range 78-1230K, in order to determine the lattice location of Hf atoms in the ordered c0–Ni3Al structure. The two NQIs obtained are discussed within the present L12 cubic structure and a tetragonal distortion of L12 to another two DO22 and L60 type structures. The first low frequency NQI at the site of the 181Ta ion-probe after substitution of aluminum for hafnium in DO22 at ambient temperature, is vQ1(300 K)¼39(1) MHz with g1¼0. The corresponding high frequency value on the second crystallographic site in L60, is vQ2(300 K)¼204(14) MHz with g2¼0.47(11). These two NQI’s have different temperature behavior. The presence of both DO22 and L60 tetragonal distortions of the parent cubic L12 lattice, detected after adding 0.2 at. % Hf, are with modulations to the lattice constant (a) with a ratio (c/a), 2.04 and 0.87, respectively. Ab initio calculations of electronic and structural properties and hyperfine parameters at the 181Ta ion probe of the c0–Ni3Al–0.2 at. % Hf alloy were performed using the full potential augmented plane wave plus local-orbital (APWþlo) method as implemented in the WIEN2k code. The accuracy of the calculations and comparison with the experimental results enabled us to identify the observed hyperfine interactions and to infer the EFG sign that cannot be measured in conventional TDPAC measurements.