Electric field gradient at Nb site in the intermetallic compounds Nb3X (X = Al, In, Si, Ge, Sn) measured by PAC

The electric field gradient (efg) at the Nb site in the intermetallic compo unds Nb3X (X = Al, In, Si, Ge, Sn) was measured by the Perturbed Angular Co rrelation (PAC) method using the well-known gamma-gamma cascade of 133 - 48 2 keV in Ta-181 from the beta(-) decay of Hf-181, substituting approximatel y 0.1 atom percent of Nb. The PAC results show that V-zz drops by nearly 40 % when X changes from Al to In, and by about 25% when X changes from Si to Ge and Sn. This behavior is most probably related to the change in the degr ee of sp hybridization in these compounds. The V-zz values of the studied c ompounds do not follow the well known universal correlation for the efg's i n non-cubic metals but the observed trend is well reproduced by results of ab-initio electronic structure calculations. In the case of Nb3Al a linear temperature dependence of the quadrupole frequencies was observed in the te mperature range of 6.5 to 1210 K.