The structural parameters, structural stability and bulk modulus in RE2Sn2O7 by first-principles calculations

A systematic density functional theory study is performed to investigate the lattice parameters, the internal positional parameter xO48f and bond length of RE2Sn2O7(RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) pyrochlores. To analyze the structural stability in extreme conditions and verify whether bond strength varies inversely to bond length in rare-earth stannate pyrochlores, the structural parameter and bonding strength under hydrostatic pressure are studied. The tight connection between the different bond length contraction and the variation of 48f oxygen positional parameter x is also discovered. We calculated the bond length and the bulk modulus of RE2Sn2O7 and found that the 〈RE–O48f〉 bond plays a predominant role in determining the bulk modulus. Meanwhile, the present calculations suggest that the “bimodal effect” also exists in rare-earth stannate pyrochlores.