Small tin oxide grains: Structural and electronic properties evaluated using the density functional theory

This study is motivated by the existence of many phases of tin oxide with a bulk crystalline structure and its purpose is the assessment if this property also applies to the clustered state of this material. Therefore small grains of a columnar and a spherical shape with a rutile lattice and a size up to 120 atoms have been considered and their structural and electronic properties are evaluated applying the Density Functional Theory. The central result of the calculations is that the rutile skeleton is retained starting from the size 20-40 atoms. The main factors contributing to this behaviour are the large interatomic distances in the rutile lattice and the irregular nature of the interatomic forces. Due to these effects, most of the structural and electronic parameters have a bulk-like behaviour with a nearly constant value. These values, however, have a clear dependence on the grain size and shape and significantly diverge from the bulk ones so that the grains have to be regarded as a new phase of the tin oxide materials.