First-principles phonon calculations of thermal expansion path of Fe2Mo Laves phase

TL;DR

This study uses first-principles phonon calculations within density functional theory to predict the anisotropic thermal expansion path of Fe2Mo Laves phase, relevant for nuclear fuel cladding design at high temperatures.

Contribution

It provides a detailed thermodynamic analysis of Fe2Mo's thermal expansion path using phonon calculations, comparing with previous Debye-Gruneisen approach, and models heat capacity and volumetric expansion.

Findings

Fe2Mo exhibits non-isotropic thermal expansion.

The calculated thermodynamic properties agree with experimental data.

The approach aids in designing fuel cladding for Generation IV reactors.

Abstract

Precipitation of the topologically close-packed Fe2Mo Laves phase at the interface between the nuclear fuel and the fuel element cladding can significantly weaken the strength characteristics of the cladding and fuel. Despite the importance of designing materials for the cladding of fuel rods, the thermodynamic properties and the trajectory of the thermal expansion path of the Fe2Mo remain poorly understood. The thermodynamic properties of the Fe2Mo have been studied using the finite-temperature quantum mechanical calculations within the frame of the density functional theory under the quasi-harmonic approximation. The vibrational contribution to the free energy was obtained using phonon calculations. The thermal expansion path of Fe2Mo was predicted by comparing between free energies calculated in different directions. A path with the least energy was chosen as the trajectory of thermal expansion. The obtained result was compared with the path calculated in previous theoretical work used the Debye-Gruneisen approach and accounted magnetic subsystem to calculate the vibrational and magnetic contributions to the free energy. This comparison reveals that these two approaches are in good agreement with each other. The work shows that the Fe2Mo possesses a non-isotropic thermal expansion. The heat capacity and volumetric expansion at constant pressure are modeled. The calculated results analyzed and are in satisfactory agreement with the experimental data. Obtained results can be useful for further design of fuel element cladding materials intended for generation IV reactors, the operating temperature of which should be above 873 K.