Temperature dependence of the electric field gradient at Ta impurities in the heavy-rare-earth metals Gd, Dy, Ho, and Er

Abstract

The time-differential perturbed-angular-correlation (TDPAC) technique has been used to study the temperature dependences of the electric field gradient (EFG) at /sup 181/Ta impurities in the heavy-rare-earth (RE) metals Gd, Dy, Ho, and Er. At room temperature the ratio ..cap alpha.. equivalent vertical-bar V/sub z/z/ (1-..gamma../sub infinity/) V/sup 1at//sub z/z vertical-bar of the measured EFG V/sub z/z and the calculated ionic EFG (1-..gamma../sub infinity/) V/sup 1at//sub z/z decreases linearly with increasing rare-earth atomic number. A linear but much stronger decrease of ..cap alpha.. has previously been reported for the impurity /sup 111/Cd. A simple model is proposed which explains the linear decrease of ..cap alpha.. and the different slopes for /sup 181/Ta and /sup 111/Cd in terms of the lanthanide contraction. This model assumes the conduction-electron contribution to the EFG to be mainly determined by the number of electrons in the Wigner-Seitz cell of the impurity. In all rare-earth hosts the EFG decreases with increasing temperature. This decrease, which is slightly stronger for Gd than for Er, is better described by a linear function of temperature than by a T/sup 3/2/ behavior, observed in many other impurity-host systems. The temperature dependence of the EFG is much stronger than expected from themore » lattice expansion. The difference between the temperature dependence of the measured EFG and of the calculated lattice EFG decreases across the rare-earth series. This can be attributed to a decrease of the amplitudes of the lattice vibrations between Gd and Er.« less