Synthesis and crystal structure characterization of InGaZnO4 with a new defect structure

Single crystals of InGaZnO4 were synthesized in a sealed Pt-tube at elevated temperatures under normal pressure without flux. InGaZnO4 has a trigonal crystal system (R3¯m; No. 166) deduced from convergent beam electron diffraction (CBED). Single crystal structure refinement from XRD data at −150 °C (a=3.275(1) Å; c=25.99(1) Å; Z=3) revealed an alternate stacking of InO6/3− and (Ga,Zn)O4/4+ layers, iso-structural to YbFe2O4. The cell parameters at room temperature were refined from powder X-ray diffraction data (a=3.284(3) Å and c=26.037(3) Å). The transparent crystals have a gray-bluish color and exhibit an excess of Ga expressed by the cation ratio of In:Ga:Zn=30.2(9):39(1):31(1) determined by energy dispersive X-ray spectroscopy (EDXS). While the isovalent substitution of In3+ by Ga3+ is known, an additional aliovalent substitution of Zn2+ by Ga3+ is observed. This results in the formula (In0.9Ga0.1)Ga1.06Zn0.91□0.03O4 where 3% of the cations in 4+1 coordination are vacant due to aliovalent substitution. Further evidence of that defect structure is found in the lattice parameter a which is substantially smaller than in stoichiometric InGaZnO4, as well as in the strong absorption in the near-IR from transitions correlated with the defect structure. The bluish color of the crystals is due to an enhanced absorption in the red of the visible spectrum. For the first time, we achieved to image InGaZnO4 at atomic resolution in the electron microscope proving a perfect periodic stacking of atomic layers. - Graphical abstract: Single crystals of InGaZnO4 have been synthesized at ambient pressure and analyzed with X-ray diffraction, electron microscopy, and optical absorption. Optical band gap and optical transmission have been determined. - Highlights: • Preparation of single crystals of InGaO3(ZnO)1 at ambient pressure for the first time. • Non-stoichiometric compound (In0.9Ga0.1)Ga1.06Zn0.91□0.03O4 with defect structure, excess of Ga, depletion of Zn. • Real structure of InGaO3(ZnO)1 imaged by high resolution TEM for the first time. • Optical band gap and transmission of InGaO3(ZnO)1 single crystal