Matthiessen's rule breakdown in some Pt- and Pd-based alloys

The deviation from Matthiessen's rule in five PtTi, five PtV, and five PdTi alloys, each containing between 0.1- and 1-at.% impurity, have been examined up to 300 K. These data for the Pt-based alloys are reasonably well fitted by a two-band model using a temperature-independent value of $\beta =0.23\mathrm{}\pm 0.02$ (PtTi) and $\beta =0.22\mathrm{}\pm 0.02$ (PtV), whereas the estimated values for $\gamma$ fall from around 0.7 at 20 K to 0.03 at room temperature. The anisotropy ratios ${\alpha }_i$ and ${\alpha }_{\rho }$ deduced from these data display a temperature variation which we find difficult to understand physically. The PdTi data are tolerably well fitted by the two-band model, although some discrepancies exist. As an alternative, the recently proposed empirical scheme of Caplin and Rizzuto is found to fit all these data well; the parameters $\rho _{}^{\prime }{}_0{}^{}\mathrm{}\left(T\right)\mathrm{}$ and $\mathrm{Kf}\left(T\right)\mathrm{}$ deduced by fitting such data are found to display a variation with temperature similar to that observed in a wide range of alloy systems. For the PdTi system in both fitting schemes it appears that there may be an additional contribution to the resistivity at low temperatures.