The Gruneisen Parameter and the Apparent Part of the General Measure of Anharmonicity of Solid Solutions of the Fe-Ni System

The temperature and concentration dependences of the nanometric parameter of crystal lattice of Fe-Ni alloys in the range of 293-973 K were studied with the high-temperature X-ray diffraction method using the "CROS"-type camera. The change of the Debye's X-ray characteristic temperature, the general measure of anharmonicity, it's implicit and explicit parts, the Grüneisen parameter were investigated. The discrepancy between the individual values and the mean values of the Grüneisen parameter was explained. One part of the research results was presented analytically and the other was presented graphically. The nature of temperature and concentration changes correlate with each other. It was investigated that for invar alloys (35-35.6 at. % Ni) the linear expansion coefficient is small, and for super invar alloys (42-48 at. % Ni) the coefficient of linear expansion is almost constant in the range of 273-573 K. In connection with these features, it was foreseen to estimate the value of the explicit part of anharmonicity measure, due to the growth of sample temperature. The temperature dependence of the lattice constant and the logarithm of the relative integral intensity of diffraction peaks reflection were investigated at room temperature and at higher temperatures. By the Chipman's method, taking into account the correction on thermal diffusive scattering, the temperature dependence of the effective X-ray characteristic temperature was determined. It was investigated that the temperature dependence of the actual coefficient of linear expansion of permalloy alloys is similar in magnitude and character. For invar alloys it differs significantly in magnitude and in character from permalloy alloys. The prospect of using a high-temperature X-ray method for determining the Grüneisen parameter in studying the structure and interatomic bonds of ferromagnetic solids was substantiated.