Drastic changes of electronic structure and crystal chemistry upon   oxidation of SnII2TiO4E2 into SnIV2TiO6: an ab initio study
  From DFT based calculations establishing energy-volume equations of state and electron localization mapping, the electronic structure and crystal chemistry changes from Sn2TiO4 to Sn2TiO6 by oxidation are rationalized; the key effect being the destabilization of divalent tin SnII towards tetravalent state SnIV leading to rutile Sn2TiO6 as experimentally observed. The subsequent electronic structure change is highlighted in the relative change of the electronic band gap which increases from ~1eV up to 2.2 eV and the 1.5 times increase of the bulk modulus assigned to the change from covalently SnII based compound to the more ionic SnIV one. Such trends are also confronted with the relevant properties of black SnIIO characterized by very small band gap. 
Samir F. Matar, Mario Maglione, Michel Nakhl, Charbel Kfoury, Jean   Etourneau
cond-mat.mtrl-sci