Ab initio investigation of properties and mobility of helium defects in La2Sn2O7 pyrochlore

•The effects of helium on the structural, electronic, and mechanical properties of La2Sn2O7 pyrochlore have been systematically investigated using first principles methods.•He atoms cause small volume swelling but no significant influence on mechanical properties of La2Sn2O7 pyrochlore.•He atom preferentially occupy octahedral interstitial site in La2Sn2O7.•He interstitial may drive phase change from pyrochlore to the fluorite structure.•The minimum energy pathway for helium to migration is identified as via O-O interstitial sites with a barrier of 1.39 eV.