Electric-field gradient at the transition-element impurityIr193in the hexagonal transition metals Sc, Y, Lu, Ti, Zr, and Hf

The electric-field gradient at the transition-element impurity ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ in the hexagonal transition metals Sc, Y, Lu, Ti, Zr, and Hf has been determined by Mössbauer measurements. The results are 42.9(11.0) × ${10}^{17}$ V/${\mathrm{cm}}^2$ in Sc, 21.5(5.5) × ${10}^{17}$ V/${\mathrm{cm}}^2$ in Y, 16.6(4.3) × ${10}^{17}$ V/${\mathrm{cm}}^2$ in Lu, 6.5(1.6) × ${10}^{17}$ V/${\mathrm{cm}}^2$ in Ti, 6.8(1.7) × ${10}^{17}$ V/${\mathrm{cm}}^2$ in Zr, and 11.6(3.0) × ${10}^{17}$ V/${\mathrm{cm}}^2$ in Hf. These results suggest that the density of states at the Fermi energy of the host and the electronic structure of the impurity are of major importance for the electric-field gradient in transition-metal alloys. The electric-field gradient of Ir in Sc is the largest value ever observed at a non-rare-earth impurity in a metallic host. In the IVb metals Ti, Zr, and Hf, the field gradient depends sensitively on the concentration of nitrogen and oxygen impurities in the samples.