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Among orbital-ordered states in manganites with strongly correlated electronic systems, both the C-type orbital-ordered (Ctype-OO) state and the charge- and orbital-ordered (COO) state have been reported in the simple perovskite Ca1−xLaxMnO3 (CLMO) with 0.15 ≦ x ≦ 0.28. To understand their formation from the disordered Pnma (DO) state with orthorhombic symmetry, the crystallographic features of prepared CLMO samples with 0.15 ≦ x ≦ 0.28 were examined mainly by transmission electron microscopy. When the temperature was lowered from the orthorhombic DO state for 0.15 ≦ x ≦ 0.23, referred to as Region I, the Ctype-OO state with monoclinic-P21/m symmetry appeared via a disordered Jahn–Teller polaron (DJTP) state, which exhibited characteristic diffuse scattering around each DO reflection in electron diffraction patterns. For 0.23 ≦ x ≦ 0.28 as Region II, cooling from the DO state resulted in the appearance of the COO state via a similar DJTP state. In patterns obtained from the COO state, satellite reflections characterizing the state were confirmed to be due to both transverse and longitudinal lattice modulations. It was also found that the DJTP states in Regions I and II were present in TN ≧ T ≧ TCtype-OO and T ≧ TCOO, respectively, and were identified as the precursor states, which appear prior to the formation of the Ctype-OO and COO states. [ABSTRACT FROM AUTHOR]

The crystallographic features of Bi1-xCaxFeO3 samples with x = 0.10, 0.15, 0.20, and 0.30 compositions are investigated by transmission electron microscopy. Perovskite-based modulated structures are found in all the samples except for the x = 0.10 sample where a rhombohedral R3c BiFeO3-type structure is observed at room temperature. The in situ heating experiment indicates that the modulated structure appears even in the x = 0.10 sample at 673K or higher. At room temperature, the modulation direction is found to change at approximately x = 0.20. The models of the modulated structures are constructed by introducing periodic antiphase boundaries in terms of the M3-type rotational displacements of the FeO6 octahedra. The electron diffraction patterns simulated from the models are in good agreement with the experimental results. The composition dependence of the modulated structures is also discussed. [ABSTRACT FROM AUTHOR]

The C- and A-type antiferromagnetic orderings have been reported in the highly correlated electronic manganite Sr1-xSmxMnO3 (SSMO) with the simple perovskite structure in the composition range of 0.34 ≤ x ≤ 0.46. Because these antiferromagnetic orderings should be coupled to orbital orderings, the crystallographic features of SSMO samples prepared with 0.15 ≤ x ≤ 0.50 have been investigated, mainly by X-ray powder diffraction and transmission electron microscopy, to understand the detailed features of the corresponding orbital-ordered states. It was found that around 100 K, for instance, the C-type orbital-ordered (COO) state was observed for 0.15 ≤ x ≤ 0.42, the orbital-modulated (OM) state for 0.44 ≤ x < 0.50, and the coexistence state of both ferromagnetic Pnma (I) and paramagnetic Pnma (II) regions for x = 0.50, where the OM state was characterized by a transverse lattice modulation with an incommensurate periodicity. Neither the A-type orbital-ordered state nor the CE-type state involving both orbital and charge modulations was found in the SSMO samples. The reasons for their absence are also discussed on the basis on the experimental data obtained in this study. [ABSTRACT FROM AUTHOR]

The mixed-oxide system (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) has a simple perovskite structure and exhibits relaxor behavior for 0 ≤ x ≤ 0.30 (low Ti contents). To understand the relaxor state in PMN–xPT, the crystallographic features of the ferroelectric states were investigated via transmission electron microscopy, taking advantage of Friedel’s law failure. Polar regions having 〈110〉C and 〈001〉C components were observed separately both below and near Tm, the maximum temperature of the dielectric permittivity for the relaxor. As a result, the relaxor state for 0 < x ≤ 0.30 was identified as an assembly of nanometer-scale polar domains with rhombohedral symmetry. On the other hand, the ferroelectric states for 0.40 ≤ x ≤ 0.70 are characterized by a ferroelectric MC-type monoclinic state, having a polarization vector in the {100}C planes. Thus, the FR/FMC boundary around x = 0.35 was identified as the morphotropic phase boundary (MPB), nearly parallel to the temperature axis. [ABSTRACT FROM AUTHOR]

A mixed-oxide system (1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3, which has a simple perovskite structure, has been reported to exhibit remarkable piezoelectric responses for 0 < x ≤ 0.08. To understand the ferroelectric states for 0 < x < 0.10, the crystallographic features of plate-shaped single crystals with various sample orientations have been examined by transmission electron microscopy. Owing to both the bending of specimens and the complicated nanometer-scale domain structures, it was difficult to obtain a contrast reversal due to the failure of Friedel's law. In some cases, however, it was possible to analyze the ferroelectric domain structures of the sample. Although the typical 109° domain structure of the ferroelectric rhombohedral state was found for x = 0.02, as a major feature in [110]c-oriented single crystals, the ferroelectric states for 0 < x ≤ 0.08 were found to be characterized by an assembly of nanometer-scale polar (NP) domains with rhombohedral symmetry. In [210]c-oriented crystals, on the other hand, the so-called MC state with monoclinic symmetry was present for x ≈ 0.08. Furthermore, on the basis of in-situ observation, the evolution of a mazepattern domain structure in the MC state upon cooling from the paraelectric state occurs via a local flip-flop between two polarization vectors, which are nearly parallel to the 〈210〉c directions. It is likely that this behavior is directly associated with the ultrahigh piezoelectric deformations found for x ≈ 0.08. [ABSTRACT FROM AUTHOR]

In the kinetic process of the fcc → L12 + D022 phase transition of the Pd3Al0.2V0.8 alloy, the suppression of atomic diffusion in the L12 regions during the evolution from the fcc + L12 intermediate state occurred under a certain thermodynamic process. Owing to this suppression, the L12 regions underwent no L12 + D022 evolution and were closed to atomic exchanges with the fcc regions. As for the fcc regions, the L12 + D022 state indeed formed but the L12 chemical composition deviated from that of the L12 regions due to a lack of mutual atomic exchange. Such independent evolutions eventually led to a formation of the metastable state with partially closed regions. From the viewpoint of the stochastic process, the L12 and fcc regions act as independent closed ensembles with different time averages along the respective probabilistic trajectories during the evolutions. Because the starting state (the fcc single phase) of the phase transition can be regarded as one canonical ensemble, the evolution to the present metastable state indicates a translation from one to two statistical ensembles in one solid state during the phase transition, the trigger for which is the suppression of atomic diffusion in the L12 regions. [ABSTRACT FROM AUTHOR]