Calculation of the Debye‐Waller Factor for Mössbauer Surface Atoms: Anisotropic Effects

Abstract

Many papers have s o far dealt with the theory of the Debye-Waller factor and its comparison with experimental data /1 t o 9/. In principle, the Debye-Waller factor can be determined by elastic X-ray o r neutron scattering. However, the accuracy of these methods is limited in comparison to what can be achieved with Mossbauer spectroscopy. The information contained in Mossbauer data is unique compared with that in most other experimental techniques used for studying lattice dynamics i n that it is connected with only one of the constituents of the crystal /lo/. This means that it contains information about the eigenvect o r s of this constituent which is hardly accessible by other methods.In a recent paper /11/ (hereafter denoted by I) wehave presented theoretical considerations about the Debye-Waller factor for Niossbauer resonant surface atoms using a linear response theory (Green functions). However, in this calculation we were restricted to the c a s e where anisotropy was not considered. It is the aim of this letter t o extend this previous work taking into account this effect.The method of calculation is identical to I (see equations (5) At high temperature, the surface atom MSD are given by with i=x,y, o r z. Here, T is the absslute temperature and kB the Boltzmann constant. The Green functions <Ui (z); Ui (z)*>>w= a r e defined by /14/ 1) 59.072 -Natal, RN, Brazil. 2) Work partially supported by the Brazilian Research Agencies CAPES, CNpq, and FINEP,