Structural relaxation of amorphousPd82Si18: X-ray measurements, electrical-resistivity measurements, and a comparison using the Ziman theory

Structural relaxation in amorphous ${\mathrm{Pd}}_{82}$ ${\mathrm{Si}}_{18}$ is studied using high-precision x-ray diffraction. The x-ray structure factor S(k) and the density ρ (determined from the x-ray absorption), are measured simultaneously as a function of the annealing conditions. The measured changes in S(k) are compared with those expected from simple densification using a Percus-Yevick model with two hard-sphere diameters. The variation in the electrical resistivity with annealing is also measured and is compared with the resistivity change estimated from the x-ray measurements using the Ziman theory. To allow a direct comparison of the x-ray and electrical measurements, we derive an approximate relationship between the x-ray atomic scattering factor and the pseudopotential as a substitute for a first-principles calculation. The combination of the low scattering rate from the amorphous samples and the high precision (<0.1%) necessary to allow direct comparison requires special techniques to maintain adequate system stability.