Electrical Resistivity, Thermoelectric Power, and X-Ray Interference Function of Amorphous Ni-Pt-P Alloys

Abstract

Amorphous alloys having the composition ${({\mathrm{Ni}}_{x}{\mathrm{Pt}}_{1\ensuremath{-}x})}_{0.75}{\mathrm{P}}_{0.25}$, where $0.20\ensuremath{\le}x\ensuremath{\le}0.60$, were obtained by rapid quenching from the liquid state. X-ray diffraction measurements indicate a high degree of structural disorder in these alloys and an atomic configuration closely similar to that in liquid metals. At room temperature, the electrical resistivity $\ensuremath{\rho}$ of these alloys lies between 160-185 \ensuremath{\mu}\ensuremath{\Omega} cm, and the absolute thermoelectric power $S$ between 1.9-2.5 \ensuremath{\mu}V/\ifmmode^\circ\else\textdegree\fi{}K. On increasing the temperature from 4.2 to 420 \ifmmode^\circ\else\textdegree\fi{}K, up to which the amorphous alloys are stable, the resistivity of the alloy with $x=0.20$ decreases by about 2%; the value of $\frac{d\ensuremath{\rho}}{\mathrm{dT}}$ progressively increases with increasing Ni content, becoming positive at $0.50<x<0.60$. In the range 80-300 \ifmmode^\circ\else\textdegree\fi{}K, the $\frac{\mathrm{dS}}{\mathrm{dT}}$ of all alloys lies between 5-8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ \ensuremath{\mu}V${\mathrm{deg}}^{\ensuremath{-}2}$. The electrical behavior of these alloys may be treated in terms of electron scattering in disordered structures assuming the nearly free-electron model, in a manner analogous to Ziman's theory of electronic transport in liquid metals. The $\frac{d\ensuremath{\rho}}{\mathrm{dT}}$ of these alloys is then qualitatively explained in terms of the temperature and composition dependence of the x-ray interference function $a(K)$, assuming an average number of \ensuremath{\sim}1.3 conduction electrons per atom in these alloys. For the alloy with $x=0.20$, this implies a Fermi energy of 6.9 eV which corresponds to the position of the first peak in $a(K)$. The thermoelectric-power results lead to the conclusion that the "average" form factor for scattering of electrons decreases with increasing Ni/Pt ratio.