The chemical bonds in MeSb 2O 4 ( Me = Mn, Ni, Fe, Zn) isomorphous compounds: Thermal expansion, force constants, energies

Abstract

The various chemical bonds ( MeO, SbO) in the MeSb 2O 4 isomorphous compounds ( Me = Mn, Ni, Fe, Zn) are characterized by four quantities: the interatomic distance ( r ij ), the force constant ( f ij ), the thermal expansion ( α ij = 1 r dr dT ), the bond energy. Using structural evolution data (neutron diffraction) and Raman infrared spectroscopic studies at low temperature (5–300 K), it has been possible to connect the various r ij , f ij , and α ij quantities with bond energies; such energies have been calculated using a simplified pair potential model U( r) = Ar − m  Br − n ; calculated force constants and thermal expansions have been derived from the derivatives d 2U dr 2 and d 3U dr 3 . For each MeSb 2O 4 compound lattice energies ( E r ) are then proposed. Using a new empirical bond-length-bond-energy method [J. Ziółkowski, J. Solid State Chem. 57, 269 and 291 (1985)] dissociation energies of MeO and SbO bonds have been evaluated for each MeSb 2O 4 compound. The total calculated dissociation energy D( MeSb 2O 4 → Me° + 2 Sb° + 40°) is then compared to the lattice energies E r obtained from the first method. The | E r | and D values are respectively about 1080 and 790 kcal · mole −1; the difference is directly linked with the ionic character of MeO bonds.