Ab initio thermodynamic properties of certain compounds in Nd-Fe-B system

Abstract

In this work, we report the results of ab initio calculations of thermochemical properties of several compounds in the Fe-Nd, B-Nd and B-Fe-Nd systems. We have performed DFT+U calculations to compute the enthalpy of formation of the compounds NdB 6 , NdB 4 , Nd 2 B 5 , Nd 2 Fe 17 and Nd 5 Fe 2 B 6 . It was found that the values obtained with an effective Hubbard U correction have better agreement with the experimental data. We have also computed the vibrational contribution to the heat capacity (C p ) of the compounds as a function of temperature was computed using the quasharmonic approximation. For most of the compounds these properties have not been experimentally determined until now. Hence, the computed ab initio thermodynamic properties will serve as useful input for the Gibbs energy model parameter assessment using the CALPHAD method.

Prediction of Lattice Constant of A2XY6 Cubic Crystals Using Gene Expression Programming

“…It is worth mentioning that formation enthalpy in (kJ or eV per mole) of each crystal is necessary to elucidate the intrinsic differences in energetic states. However, it is documented that the A 2 XY 6 are much more stable crystals compared to other crystals such as AXY 3 . − Some of the literature reported formation enthalpies of A 2 XY 6 compounds such as fluorides, mainly by using some calculation approaches such as the Born–Fajans–Haber thermochemical cycle …”

Development of a prototype thermodynamic database for Nd-Fe-B permanent magnets

“…One of the major problems pointed out in these assessments is the uncertainty of the phase equilibria between liquid and borides in the B-Nd binary system assessed by Hallemans et al [ 56 ]. Recently, Hanindriyo et al [ 86 ] reconsidered the stability of borides in the B-Nd system on the bases of theoretical calculations. For expansion to higher-order systems, and to improve the descriptions of the Gibbs energy, the Gibbs energy functions adopted in the present work are based on the assessment of Hallemans et al In the previous assessments [ 56 , 82–86 ], there is one significant uncertainty, which is the Gibbs energy of the Nd 2 Fe 14 B phase because the heat capacity of the compound is not well characterized at high temperatures where the magnetic transition occurs.…”

“…Phase names, constituents and sublattices, Structure type, and Pearson symbols included in this database where "Va" denotes vacancy and Phases with "*" are not unified.Nd system on the bases of theoretical calculations. For expansion to higher-order systems, and to improve the descriptions of the Gibbs energy, the Gibbs energy functions adopted in the present work are based on the assessment of Hallemans et al In the previous assessments[56,[82][83][84][85][86], there is one significant uncertainty, which is the Gibbs energy of the Nd 2 Fe 14 B phase because the heat capacity of the compound is not Fe 14 B. According to their experimental results, it has a T C and the magnetic moment are 585.3 K and 2.04, respectively.…”

“…One of the major problems pointed out in these assessments is the uncertainty of the phase equilibria between liquid and borides in the B-Nd binary system assessed by Hallemans et al[56]. Recently, Hanindriyo et al[86] reconsidered the stability of borides in the Bwell characterized at high temperatures where the magnetic transition occurs. To improve on this uncertainty, Morishita et al[87] measured the heat capacity of…”