Extended x-ray absorption fine-structure determinations of coordination numbers: Limitations

Comparisons are made between measured extended x-ray absorption fine-structure (EXAFS) amplitudes for nearest- and more-distant-neighbor coordination shells in a wide variety of known compounds at both room temperature and 77 K. The comparisons reveal a significant sensitivity of the amplitudes to the chemical environment and non-Gaussian disorder. The observed changes can cause significant errors in the empirical determinations of coordination numbers. The absence of the possibility of a quantitative theoretical calculation of the EXAFS amplitude leads to the conclusion that coordination numbers can be determined most accurately by the use of a chemically and structurally similar model measured at low temperature.