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 Cmc2₁ (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).