High-resolution electron microscopy of a modulated structure in InMO₃(ZnO)_m (M = In, Fe, Ga, and Al; m = integer): effect of solid solution formation

Abstract

The structure of InMO₃(ZnO)_m (M = In, Fe, Ga, and Al; m = integer) is built from InO₂¹⁻ (In–O) and MZn_m,O_m+1^1m (M/Zn–O) layers stacked alternately. A modulated structure of these compounds results from the ordering of M ions in the M/Zn–O layers. The modulated structures of InMO₃(ZnO)₁₃ (M = In_0.5A_0.5; A = Fe, Ga, and Al), a solid solution of InInO₃(ZnO)₁₃ and InMO₃(ZnO)₁₃ (M =Fe, Ga, and Al), have been studied by high-resolution electron microscopy. The main and satellite spots of the electron diffraction patterns are indexed as ha* + kb* + lc* + mq by using the four dimensional superspace group approach. Based on the crystal system of the basic structure and the modulation wave vector q, the electron diffraction patterns are classified according to three categories with typical parameters: (1) monoclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, β = 93° and q = b*/18.1; (2) monoclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, β = 93°, and q = b*/22.5 + c*/2; (3) triclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, α = 95°, β = 95°, γ = 30°, and q = a*/12.1 + b*/18.1 + c*/32.3. Among these, the first is the same as that of their constituent compounds In₂O₃(ZnO)₁₃ and InMO₃(ZnO)₁₃ (M = Fe, and Ga), while the second and the third are different. In high-resolution image, the modulated structure appears as zig-zag contrast within the M/Zn–O layers. The periodicity of this zig-zag contrast along the M/Zn–O layer in InMO₃(ZnO)₁₃ (M = In_0.5A_0.5; A = Fe, Ga, and Al) is between those of InInO₃(ZnO)₁₃ and InMO₃(ZnO)₁₃ (M = Fe, Ga, and Al).