Mechanical properties, thermal conductivity and defect formation energies of samarium immobilization in Gd₂Zr₂O₇: First-principles study and irradiation experiment

A density functional theory (DFT) study was employed to investigate the mechanical property, thermal conductivity, Debye temperature, electronic structure and defect chemistry of (Gd_1–xSm_x)₂Zr₂O₇. All the (Gd_1–xSm_x)₂Zr₂O₇ compounds exhibit an excellent structural and mechanical stability (Gd_0.25Sm_0.75)₂Zr₂O₇ has the lowest Young's modulus of 213.7 GPa, the largest Possion's ratio of 0.292, the lowest Debye temperature of 491.8 K and the lowest thermal conductivity. The calculated thermal conductivities of (Gd_1–xSm_x)₂Zr₂O₇ are 1.17–1.21 W/(m·K) by the Clark's model and 1.32–1.36 W/(m·K) by the Cahall's model, respectively. The formation energies of O vacancies at 48f site are negative, which increase with the Sm content, however, the formation energies of O vacancies at 8b site are almost invariable. In addition, Sm partly occupying the Gd-site reduces distinctly the formation energies of defects such as A-site vacancies, cation antisite defects, anion Frenkel pairs of oxygen at 8b site and cation interstitials, which suggests that Sm-doped Gd₂Zr₂O₇, especially equimolar GdSmZr₂O₇, has a better irradiation tolerance. After the 16 MeV Ta-ion irradiation at a fluence of 1 × 10¹⁴ or 2 × 10¹⁴ ions/cm², the crystal structure of GdSmZr₂O₇ transforms from pyrochlore to a defect fluorite without obvious amorphous phase.