Structure analysis of new homologous compounds Ga2O3(ZnO)m (m = integer) by high-resolution analytical transmission electron microscopy

The crystal structure of a new homologous compound series, Ga2O3(ZnO)(m) (m = integer), is determined by high-resolution lattice imaging and high spatial resolution energy-dispersive X-ray spectroscopy (EDS) analysis in a field-emission analytical transmission electron microscope. This work was carried out mainly on the compound with m = 9 (digallium nonazinc dodecaoxide), which belongs to the orthorhombic system and has lattice constants a(o) = 0.33, b(o) = 2.0 and c(o) = 3.4 nm. From the extinction rules three possible space groups are selected and from them a unique space group is assigned as noncentrosymmetric Cmc2(1) (No. 36) on the basis of structural requirements. Ga2O3(ZnO)(m) is a layered structure consisting of Ga-O and m + 1 Ga/Zn-O layers stacked alternately along the c axis. It is shown that the structure of Ga2O3(ZnO)(m) differs from that of M2O3(ZnO)(m) (M = In, Fe; m = integer) reported previously In Ga2O3(ZnO)(m) the Ga atoms occupy the tetrahedral sites in the Ga-O layers, whereas the M atoms in the M-O layers occupy the octahedral sites in M2O3(ZnO)(m) (M = In, Fe).