Structural and bonding properties of stannate pyrochlores: A density functional theory investigation

Low-temperature heat capacity of samarium zirconate (Sm2Zr2O7)

“…Since REM zirconates and stannates have similar cubic structures and close lattice parameters, it is assumed that, as a first approximation, interaction between Ln 3+ and oxygen anions in these compounds will be similar as well. Figure 3 shows the standard heat capacities of REM zirconates and ionic charges of lanthanides and oxygen (O 48f , O 8b ) and occupation densities for Ln-O 48f and Ln-O 8b bonding in REM stannates calculated in [22]. As is obvious, the highest absolute charges are shown by Sm 3+ and O 2-48f in Sm 2 Sn 2 O 7 , which is indicative of stronger interaction between these ions.…”

“…The difference in the phonon spectra of isostructural solids may be due to distinct masses of their particles and bonding energy between them. We believe that the mass of oscillating atoms insignificantly increasing (by no more than 10%) from La to Gd in the series La 2 [22] of REM zirconates. Nevertheless, electrostatic charges and occupation density are calculated in [22] with the Hirshfeld method to understand the chemical bonding and its effect on the stability of pyrochlore-like compounds such as Ln 2 Sn 2 O 7 (Ln⎯La, Pr, Nd, Sm, Gd).…”

“…We believe that the mass of oscillating atoms insignificantly increasing (by no more than 10%) from La to Gd in the series La 2 [22] of REM zirconates. Nevertheless, electrostatic charges and occupation density are calculated in [22] with the Hirshfeld method to understand the chemical bonding and its effect on the stability of pyrochlore-like compounds such as Ln 2 Sn 2 O 7 (Ln⎯La, Pr, Nd, Sm, Gd). Since REM zirconates and stannates have similar cubic structures and close lattice parameters, it is assumed that, as a first approximation, interaction between Ln 3+ and oxygen anions in these compounds will be similar as well.…”

“…As is obvious, the highest absolute charges are shown by Sm 3+ and O 2-48f in Sm 2 Sn 2 O 7 , which is indicative of stronger interaction between these ions. In addition, analysis of the orbital population densities [22] demonstrates that samarium stannate has the strongest Ln⎯O 48f bonding, which is evidence of a high degree of covalence. That is, the energy of cohesion between Sm 2 Zr 2 O 7 atoms will probably be maximum as compared with other isostructural REM zirconates, the lattice will become more rigid, and the atomic oscillation frequency will increase.…”

In situ studies of ion irradiated inverse spinel compound magnesium stannate (Mg2SnO4)

“…The difference of electronegativity between Sn and O is smaller than Al and O and also smaller than Mg and O, suggesting that the covalency of hSn-Oi bond is higher than hAl-Oi and hMgOi, and Mg 2 SnO 4 is more covalently bonded than MgAl 2 O 4 . Similarly in pyrochlore stannate compounds, high covalency of hSn-Oi bond has also been found both experimentally using neutron and X-ray diffraction and theoretically using density functional theory (DFT) computer simulation [41][42][43][44]. Therefore, the high covalency of hSn-Oi bond in Mg 2 SnO 4 may cause the structure more susceptible to irradiation damage than MgAl 2 O 4 .…”