Au197Mössbauer line shape and recoilless fraction as a function of temperature and lattice order inCu3Au

Mössbauer spectra have been measured for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ in ordered and disordered ${\mathrm{Cu}}_3$Au absorbers as a function of absorber thickness and temperature. The measured line shapes are found to be sensitive to lattice order and have been interpreted in terms of two parameters which are found to be order dependent. The first parameter is a pseudoquadrupole splitting which has been introduced to describe line broadening due to noncubic local atomic environments of gold atoms in ${\mathrm{Cu}}_3$Au. The second is the temperature-dependent recoilless fraction for gold in ${\mathrm{Cu}}_3$Au. An iterative procedure has been used to fit an appropriate line-shape function to ${\mathrm{Cu}}_3$Au spectra measured at 4.2 K. From this procedure, it is found that the pseudoquadrupole splitting is smaller and the recoilless fraction is larger for the more highly ordered state. Precise values of the recoilless fraction and the corresponding effective Debye temperature for gold in ${\mathrm{Cu}}_3$Au have also been determined from thick-absorber line-shape measurements in the temperature range 4.2-100 K. Measurements of the isomer shift for gold in ${\mathrm{Cu}}_3$Au as a function of order and temperature are also given.