Effect of oxygen on the stability of one dimensional long period superstructures in Cu 3Pd

Abstract

This paper reports that high resolution electron microscopy (HREM) studies of Cu-Pd alloys have revealed that the antiphase boundaries (APB), associated with the LPS formed at low temperatures, exhibit a sharp character, while those in LPS equilibrated at high temperatures are diffuse (the diffuse character of APBs can be ascribed to disorder along the boundary or to small fluctuations of the positions of the APB). In a recent theoretical study, sharp and diffuse characters of APB at various temperatures were attributed to flat sections on the Fermi surface of Cu-Pd alloys, which produce a deep minimum in V(k), the Fourier transform of the effective pair interactions: At high temperature, the deep minimum in V(k) quickly diminishes the amplitude of the Fourier components of the modulation wave that are located away from the V(k) minimum, which leads to a smooth modulation profile. Consequently, in selected area diffraction patterns (SAD), only first order satellites are expected. On the other hand, at lower temperatures, where the contribution from the Fourier component of the modulation wave away from the minimum in V(k) is also significant, higher order satellites should be observable in SAD patterns. These prediction agree with experimental results.