In this study, a density functional theory method is employed to investigate the effects of isovalent and aliovalent substitution of Sm 3+ on the phase stability, thermo-physical properties and electronic structure of Gd 2 Zr 2 O 7 . It is shown that the isovalent substitution of Sm 3+ for Gd 3+ results in the formation of Gd 2 Zr 2 O 7 -Sm 2 Zr 2 O 7 solid solution, which retains the pyrochlore structure and has slight effects on the elastic moduli, ductility, Debye temperature and band gap of Gd 2 Zr 2 O 7 . As for the aliovalent substitution of Sm 3+ for Zr 4+ site, a pyrochlore-to-defect fluorite structural transition is induced, and the mechanical, thermal properties and electronic structures are influenced significantly. As compared with the Gd 2 Zr 2 O 7 , the resulted Gd 2 Sm y Zr 2-y O 7 compositions have much smaller elastic moduli, better ductility and smaller Debye temperature. Especially, an amount of electrons distribute on the fermi level and they are expected to have larger thermal conductivity than Gd 2 Zr 2 O 7 . This study suggests an alternative way to engineer the thermo-physical properties of Gd 2 Zr 2 O 7 and will be beneficial for its applications under stress and high temperature.The rare-earth zirconates, with chemical formula A 2 Zr 2 O 7 (A = Y or another rare earth elements) 1, 2 , exhibit ordered pyrochlore-type structure or defect fluorite-type structure, which is mainly governed by the ionic radii of A 3+ and Zr
4+3. They have attracted the attention of many researchers, due to their good chemical and mechanical stability, excellent catalytic activity, high ionic conductivity, ferromagnetism, luminescence as well as strong resistance to amorphization under irradiation [4][5][6][7][8] . Owing to these outstanding properties, the rare-earth zirconates have a wide range of technical applications, e.g., ceramic thermal barrier coating 9, 10 , oxidation catalyst 5, 11 , solid electrolyte 12
