Temperature and concentration dependence of the electrical resistivity of α-Hf-O-, α-Hf-N and α-Hf-C-solid solutions

The electrical resistivity, rho, of α-Hf and of the solid solutions of α-Hf with O, N or C has been investigated in the hexagonal α-phase range at temperatures, T, between 200 and 300 K and between 1300 and 2000 K. For pure α-Hf, rho increases linearly with T only at the lower T, deviating from a temperature proportionality in the direction of a better conductivity at higher T. This effect is increased by dissolved nonmetals O, N or C. At higher nonmetal concentrations, Csub(x), and at a sufficiently high T, rho (T), passes a maximum and then decreases (negative temperature coefficient of electrical resistivity, i.e. semiconductor effect). At constant T, rho (csub(x)) increases in the α-phase range up to the solubility limit approximately proportional to csub(x). Therefore, the specific change in Δrho/csub(x) is approximately independent of the nonmetal concentration. However, contrary to Matthiessen's rule, Δrho/csub(x) is strongly T-dependent. Thus, the relation rho(T, csub(X)) = rho(T) + Δrho(T, csub(x)) is valid. At 300 K (2000 K) the Δrho/csub(x)-values for the solution of O, N, and C in α-Hf amount to: 9,5 (2,95) μΩ x cm x (% O/Hf)-1; 9,7 (3,00) μΩ x cm x (%N/Hf)-1 and 13,9 (2,75)μΩ x cm x (% C/Hf)-1. The results of these investigations are compared with the resistivity data of the hexagonal α-phases of the IVa metals Ti and Zr and their solid solutions with non-metals. A discussion of the data is based on a model in which the complicated electronic structure of the group IVa metals is replaced by a two-conduction band scheme. (orig.)