First-Principles Calculations of the Solution Enthalpy and the Excess Entropy of Zr in αU
The solution enthalpy and the excess entropy of Zr in αU have been calculated based on the first principles calculations in order to achieve U-rich solubility curves for U-Zr phase diagram.The solution enthalpy and the excess entropy of the Zr atom corresponding to Zr-αU transforming from solution state into δUZr2 are 1.437 eV/Zr atom and 1.060 kB/Zr atom by the SQS model,and they are 1.420 eV/Zr atom and 0.732 kB/Zr atom by the disorder structure for δUZr2.But based on the experimental data,the fitted solution enthalpy and excess entropy are-0.823±0.712 meV/Zr atom and 5.880±9.976 kB/Zr atom,respectively.The comparison between the theoretical calculations and the experimental fitting results show that the effect of the vibrational entropy on solubility can not be ignored.This discrepancy between the theoretical results and the experimental data may be related to the fact that the positions of Zr in δUZr2 in the theoretical calculations are not well consistent with the specific structural parameters of the the experimental samples.