Isotopic effects in Debye-Waller factor and in EXAFS studied based on anharmonic correlated Einstein model

Isotopic effects in Debye-Waller factor and in extended X-ray absorption fine structure (EXAFS) have been studied. The studies are succeeded based on anharmonic correlated Einstein model for isotopes derived for providing analytical expressions of cumulants containing isotopic effects and for application of these cumulants to EXAFS of isotopes. Advantageous development here is creation of a method giving not only the isotopic effects but also the considered quantities only from second cumulant. The model is simplified by using one-dimension with taking many-body effects into account based on including nearest neighbor contributions to vibrations between absorber and backscatterer isotopic atoms. Morse potential is assumed to describe single-pair isotopic atomic interaction. Isotopic effects evidenced in cumulants, EXAFS spectra and their Fourier transform magnitudes of Ni isotopes calculated by present theory are found to be in good similarity to those obtained in experimental results of 70Ge and 76Ge. •Anharmonic correlated Einstein model derived to study Debye-Waller factor, EXAFS of isotope.•Derived analytical expressions of all considered quantities contain evidenced isotopic effects.•Method is created giving isotopic effects of all considered quantities only from second cumulant.•Isotopic effects are significant at low-temperatures so they are evaluated only by quantum theory.•Calculated isotopic effects in Ni isotopes are similar to those of measured results of 70Ge, 76Ge.