Gui Jia-nian

Orientational domains at room temperature in La0.33Ca0.67MnO3 perovskite

Orientational domains at room temperature in orthorhombic perovskite La0.33Ca0.67MnO3 were studied by group-theory and observed systematically using transmission electron microscopy. There are six orientational variants (A, A′, B, B′, C andC′) in orthorhombic perovskite La0.33Ca0.67MnO3. Their orthorhombicbo directions are parallel to theap,bp andcp directions of the cubic prototypic perovskite, respectively. In each case there are two orientational variants (e.g.,A andA′) with theirao andco axes interchanged. Among the possible 15 boundaries between these 6 variants there are only two types of domain boundaries: (1) m<100>boundariesC′/C, A′/A, andB′/B. (2) m<110>boundaryiesC′/A, C′/A′, C′/B, C′/B′, C/A, C/A′, C/B, C/B′, B′/A, B′/A′, B/A, andB/A′.

Experimental Observation on Orientation Relationship between Binary Cd5.7Yb Quasicrystal and its Crystalline Approximant Cd6Yb

Similarity in the electron diffraction patterns of the Cd5.7Yb icosahedral quasicrystal and its cubic approximant Cd6Yb crystal is studied in detail by using transmission electron microscopy. The icosahedral twofold axes are parallel to the cubic 1ττ2 (τ = 1.618...) or 0 0 1 directions, the icosahedral pseudo-twofold axes are parallel to the cubic 15 21 25 directions, the icosahedral threefold axes are parallel to the cubic 1 1 1 and the icosahedral fivefold are parallel to the cubic 0 1 τ directions. Based on those observations a general stereographic projection is given to illustrate the exact orientation relationship.

Synthesis of and incommensurate charge and orbital ordering in La1/2Sr3/2MnO4 layered perovskite

Polycrystalline bulky samples of La1/2Sr3/2MnO4 were systhesized by conventional solid-state reaction in air. Composition analysis by energy dispersive X-ray spectrometer indicated that the average composition of the sample is La0.45 Sr1.49 MnO4 with a minor fluctuation. The [001] zone-axis electron diffraction patterns taken at about 100 K revealed the presence of superlattice peaks, due to the incommensurate charge and orbital ordering. The incommensurate modulation wave vector is k = δ[110]T*, with δ = 0. 19. Such an incommensurate modulation may be described as a random distribution of two commensurate modulations with δ= 1/4 and 1/6.