Effect of oxygen deficiency on Charge Ordering in La0.5Ca0.5MnO3-δ

2001 ◽  
Vol 7 (S2) ◽  
pp. 376-377
Author(s):  
J. Tao ◽  
N. Jiang ◽  
J.C.H. Spence
Keyword(s):  
Oxygen Deficiency ◽  
Charge Ordering ◽  
Orbital Ordering ◽  
Lattice Constants ◽  
Transmission Electron ◽  
Proposed Model ◽  
Jahn Teller ◽  
Diffraction Patterns ◽  
Effect Of Oxygen ◽  
Modulation Wave Vector

Elastically-filtered transmission electron diffraction patterns of La0.5Ca0.5MnO3-δ have been obtained between 105K to 288K using the Leo 912 Omega. On heating La0.5Ca0.5MnO3 undergoes a transition from antiferromagnetic insulator to ferromagnetic metal (TN ∼ 150K) and then to paramagnetic insulator (Tc ∼ 230K) . The q modulation wave vector along the b-axis direction arises from charge ordering of Mn3+ and Mn4+, and orbital ordering of dz22 orbitals associated with Jahn-Teller distortions in the Mn3+O6 octahedra at low temperature. Both the intensity and the position of superlattice peaks change as a function of temperature during heating. The large incommensurability we see between 105K to 260K differs from that seen previously and proposed model. Figure 1 a) shows the lattice constants a, b, c related to the simple perovskite lattice parameters ap (ap ∼ 3.9Å) by a≈b≈ap and c≈2ap, and indicates the octahedral coordination.

Possible Orbital-Ordered State in the Highly-Correlated Electronic Material Sr1-xCexMnO3

2014 ◽  
Vol 922 ◽  
pp. 230-236
Author(s):  
Takehiro Hanaoka ◽  
Yasuhide Inoue ◽  
Yasumasa Koyama
Keyword(s):  
Room Temperature ◽  
Three Dimensional ◽  
Electronic System ◽  
Careful Analysis ◽  
Perovskite Manganite ◽  
Orbital Ordering ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Diffraction Patterns ◽  
Highly Correlated

The simple perovskite manganite Sr1-xCexMnO3 (SCMO) has a highly-correlated electronic system with a three-dimensional character. Because the presence of orbital-ordered states of eg electrons can be expected in SCMO, the crystallographic features of SCMO samples with 0.09 ≤ x ≤ 0.20 have been investigated mainly by transmission electron microscopy. In addition to fundamental reflections due to the simple perovskite structure, their electron diffraction patterns at room temperature exhibited both the presence of superlattice reflections at k = ()c in the cubic notation and the splitting of fundamental and superlattice reflections. The careful analysis of these reflections indicated that the superlattice reflections originated from the R25-type rotational displacement of oxygen octahedra about one of the <100>c directions. On the other hand, the splitting of the reflections was found to be due to a {110}c banded structure consisting of two tetragonal bands with different c/a values.　Because one of two tetragonal bands had the c/a value of about 1.028, the splitting reflects the introduction of the Jahn-Teller distortion as a response of a lattice system to orbital ordering. It is thus understood that the C-type orbital ordering of eg electrons should be involved in the state at room temperature for 0.09 ≤ x ≤ 0.20 in SCMO.

Computer-Aided Indexing and Simulation of Transmission Electron Diffraction Patterns

1975 ◽  
Vol 33 ◽  
pp. 222-223
Author(s):  
Prakash Rao ◽  
R. P. Goehner
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Computer Programs ◽  
Transmission Electron Diffraction ◽  
Lattice Constants ◽  
Transmission Electron ◽  
Computer Aided ◽  
Flow Diagrams ◽  
Diffraction Patterns ◽  
Orientation Determination

The process of indexing electron diffraction patterns is well established and reasonably straightforward. However, in the more complicated crystal systems (e.g. hexagonal, rhombohedral, orthorhombic and monoclinic), indexing and orientation determination is not always simple. In order to considerably ease the tedium of routinely indexing such electron diffraction patterns, automation of the procedure has been carried out in our laboratory by the use of two computer programs written in conversational Fortran.Simplified flow diagrams of the two programs are shown in Figure 1. The first program (Figure 1a) indexes diffraction spots whose x and y coordinates are obtained from an experimental pattern and supplied, along with crystal structure, lattice constants, space group restrictions, camera constant, and the position and angle errors allowable.

CHARGE AND ORBITAL ORDER IN THE ELECTRON DOPED MAGNANITE (Bi,Ca)MnO3

2002 ◽  
Vol 16 (11n12) ◽  
pp. 1661-1666 ◽  
Author(s):  
P. D. HATTON ◽  
S. B. WILKINS ◽  
P. D. SPENCER ◽  
D. MANNIX ◽  
S. D. BROWN ◽  
...  
Keyword(s):  
Transition Metal Oxides ◽  
High Energy ◽  
Charge Ordering ◽  
Orbital Ordering ◽  
Orbital Order ◽  
X Ray ◽  
X Ray Scattering ◽  
Jahn Teller ◽  
Structural Modulation ◽  
Ray Scattering

The interplay between charge, spin and orbital degrees of freedom in transition metal oxides has been a matter of much interest in recent years. In this paper we present X-ray scattering results of charge and orbital ordering in the electron doped manganite Bi 0.24 Ca 0.76 MnO 3. Using High Energy X-ray Scattering (HEXS) the charge ordering, structural modulation due to the Jahn–Teller ordering and the harmonic of the structural modulation have been measured. The superlattice reflections due to the Jahn–Teller ordering are found to maximise in intensity at the Neél point. We have confirmed using resonant X-ray scattering at the K-edge of manganese and the Anisotropic Tensor of Susceptibility technique (ATS) that superlattice reflections occurring at a modulation wavevector of (0.5, 0, 0) are due to charge ordering in a Mn 3+/ Mn 4+ ordering pattern. In addition superlattice reflections corresponding to the orbital order were measured at a modulation wavevector of (0.25, 0, 0). The temperature dependence of both the Jahn–Teller structural distortion peak (1.75, 2, 0) and the charge ordering peak (3 0 0) were observed to behave identically, gradually increasing with decreasing temperature.

Transmission Electron Microscopic Study on Thermal Decomposition Process of Calcium-Deficient Hydroxyapatite

2006 ◽  
Vol 317-318 ◽  
pp. 785-788
Author(s):  
Masato Tamai ◽  
Koji Nishio ◽  
Toshiyuki Isshiki ◽  
Atsushi Nakahira
Keyword(s):  
Metastable Phase ◽  
Molar Ratio ◽  
Electron Microscopic ◽  
Thermal Decomposition Process ◽  
Transmission Electron Microscopic Study ◽  
Lattice Constants ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Transmission Electron Microscopic ◽  
Diffraction Patterns

In our previous study, we reported that a metastable phase with high Ca/P molar ratio appeared in the temperature range from 700 οC to 800οC The purpose of this study is to investigate the crystallographic relationship between the metastable phase and HAp matrix. Ca-def HAp was annealed at 500-1000' ο C in air. High-resolution transmission electron microscopic (HRTEM) observations were performed along the [010], [110] and [001] zone axes in order to investigate the structure of the metastable phase. From HRTEM images and results of the analysis of selected area electron diffraction patterns along [010], [110] and [001] zone axes, the lattice constants of the metastable phase were analyzed into a=2.86nm, b=0.94nm, and c=0.69nm of an orthorhombic crystals system.

Stability of the Orbital-Modulated State in the Layered Perovskite Manganite Sr2-xRxMnO4 (R = Pr, Nd)

2010 ◽  
Vol 638-642 ◽  
pp. 1760-1765 ◽  
Author(s):  
Yasuhide Inoue ◽  
Masazumi Arao ◽  
Go Shindo ◽  
Yasumasa Koyama
Keyword(s):  
Electron Concentration ◽  
Charge Ordering ◽  
Layered Perovskite ◽  
Perovskite Manganite ◽  
Orbital Ordering ◽  
Transmission Electron ◽  
Neighboring State ◽  
Coprecipitation Technique ◽  
The Stability ◽  
Average Size

To understand a stability of the orbital-modulated (OM) state in Sr2-xRxMnO4 (R = Pr, Nd), the crystallographic features of oxide samples with 0.20 < x ≤ 0.50, prepared by the coprecipitation technique, have been investigated by transmission electron microscopy. When the Pr content x corresponding to the eg-electron concentration increased from x = 0, the OM state appeared in 0.20 < x ≤ 0.40 as a neighboring state of an orbital ordered (OO) state around x = 0.20. The interesting features are that around x =　0.44 there is a nanometer-sized coexisting state consisting of the OM and disordered tetragonal (DT) states, and that an average size of OM-state regions in the coexisting state decreases with increasing the eg-electron concentration. In addition, the so-called CE-type antiferromagnetic state found in Sr1.5La0.5MnO4 is absent in the Nd and Pr cases. This suggests that the stability of the OM state is not directly associated with charge ordering of eg electrons, but basically due to only their orbital ordering.

Microstructure and Ferroelectric Domains of SrBi2Ta1.6Nb0.4O9

2007 ◽  
Vol 353-358 ◽  
pp. 3136-3139
Author(s):  
Hua Ke ◽  
Xiao Jing Kou ◽  
Zhe Lu ◽  
He Jun Li ◽  
Wen Wang ◽  
...  
Keyword(s):  
Domain Walls ◽  
Large Strain ◽  
Large Strains ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lattice Constants ◽  
Transmission Electron ◽  
Ferroelectric Domains ◽  
Diffraction Patterns ◽  
Relationship Of

The microstructure and ferroelectric domains of SrBi2Ta1.6Nb0.4O9 ceramics were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS). The X-ray diffraction patterns show that the lattice constants a and b decrease, and c increases by doping with Nb into SBT sample. Accordingly, it has large strain and lattice distortion in the lattice This suggests that the Nb atoms partially occupy the location of the Ta atoms in the lattice. From TEM observations, the grains show (008) preferred orientations in the sample, which agrees well with the XRD results. The 90° domain walls are identified by the 90° rotation relationship of the electron diffraction pattern about the [001] zone axis. The 180° domain walls and anti-phase boundaries (APBs) in Nb-doped SBT ceramics are also observed, which are irregularly shaped and highly curved. The traditional α-fringes can be found in the Nb-doped SBT ceramics, which are the evidence of large strains in the lattice.

Electronic Cone Illumination with the Conventional Transmission Electron Microscope

1977 ◽  
Vol 35 ◽  
pp. 72-73
Author(s):  
William Krakow
Keyword(s):  
Electronic Device ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Hollow Cone ◽  
Transmission Electron ◽  
Lissajous Figures ◽  
High Resolution Images ◽  
Imaging Mode ◽  
Diffraction Patterns ◽  
Transmission Microscope

An electronic device has been constructed which manipulates the primary beam in the conventional transmission microscope to illuminate a specimen under a variety of virtual condenser aperture conditions. The device uses the existing tilt coils of the microscope, and modulates the D.C. signals to both x and y tilt directions simultaneously with various waveforms to produce Lissajous figures in the back-focal plane of the objective lens. Electron diffraction patterns can be recorded which reflect the manner in which the direct beam is tilted during exposure of a micrograph. The device has been utilized mainly for the hollow cone imaging mode where the device provides a microscope transfer function without zeros in all spatial directions and has produced high resolution images which are also free from the effect of chromatic aberration. A standard second condenser aperture is employed and the width of the cone annulus is readily controlled by defocusing the second condenser lens.

Deviations from Ideal Decagonal Symmetry in Electron Diffraction Patterns of the “Decagonal” Phase in the Al-Co-Cu Alloy System

1991 ◽  
Vol 49 ◽  
pp. 914-915
Author(s):  
Atul S. Ramani ◽  
Earle R. Ryba ◽  
Paul R. Howell
Keyword(s):  
Electron Microscope ◽  
Alloy System ◽  
Nominal Composition ◽  
Dimensional Lattice ◽  
3 Dimensional ◽  
Decagonal Phase ◽  
Cu Alloy ◽  
Transmission Electron ◽  
Lattice Periodicity ◽  
Diffraction Patterns

The “decagonal” phase in the Al-Co-Cu system of nominal composition Al65CO15Cu20 first discovered by He et al. is especially suitable as a topic of investigation since it has been claimed that it is thermodynamically stable and is reported to be periodic in the dimension perpendicular to the plane of quasiperiodic 10-fold symmetry. It can thus be expected that it is an important link between fully periodic and fully quasiperiodic phases. In the present paper, we report important findings of our transmission electron microscope (TEM) study that concern deviations from ideal decagonal symmetry of selected area diffraction patterns (SADPs) obtained from several “decagonal” phase crystals and also observation of a lattice of main reflections on the 10-fold and 2-fold SADPs that implies complete 3-dimensional lattice periodicity and the fundamentally incommensurate nature of the “decagonal” phase. We also present diffraction evidence for a new transition phase that can be classified as being one-dimensionally quasiperiodic if the lattice of main reflections is ignored.

An Interactive Minicomputer Program for the Indexing and Simulation of Electron Diffraction Patterns

1976 ◽  
Vol 34 ◽  
pp. 542-543
Author(s):  
R.P. Goehner ◽  
W.T. Hatfield ◽  
Prakash Rao
Keyword(s):  
Electron Diffraction ◽  
Real Time ◽  
Pattern Analysis ◽  
Flow Diagram ◽  
Hard Copy ◽  
Time Analysis ◽  
Real Time Analysis ◽  
Transmission Electron ◽  
One Step ◽  
Diffraction Patterns

Computer programs are now available in various laboratories for the indexing and simulation of transmission electron diffraction patterns. Although these programs address themselves to the solution of various aspects of the indexing and simulation process, the ultimate goal is to perform real time diffraction pattern analysis directly off of the imaging screen of the transmission electron microscope. The program to be described in this paper represents one step prior to real time analysis. It involves the combination of two programs, described in an earlier paper(l), into a single program for use on an interactive basis with a minicomputer. In our case, the minicomputer is an INTERDATA 70 equipped with a Tektronix 4010-1 graphical display terminal and hard copy unit.A simplified flow diagram of the combined program, written in Fortran IV, is shown in Figure 1. It consists of two programs INDEX and TEDP which index and simulate electron diffraction patterns respectively. The user has the option of choosing either the indexing or simulating aspects of the combined program.

Effects of High-Energy Ions on Synthetic Quartz

1972 ◽  
Vol 30 ◽  
pp. 544-545
Author(s):  
Joseph J. Comer ◽  
Charles Bergeron ◽  
Lester F. Lowe
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Beam ◽  
High Energy ◽  
Transmission Electron ◽  
Kikuchi Lines ◽  
High Energy Ions ◽  
Diffraction Patterns ◽  
Dauphiné Twinning ◽  
Beam Damage

Using a Van De Graaff Accelerator thinned specimens were subjected to bombardment by 3 MeV N+ ions to fluences ranging from 4x1013 to 2x1016 ions/cm2. They were then examined by transmission electron microscopy and reflection electron diffraction using a 100 KV electron beam.At the lowest fluence of 4x1013 ions/cm2 diffraction patterns of the specimens contained Kikuchi lines which appeared somewhat broader and more diffuse than those obtained on unirradiated material. No damage could be detected by transmission electron microscopy in unannealed specimens. However, Dauphiné twinning was particularly pronounced after heating to 665°C for one hour and cooling to room temperature. The twins, seen in Fig. 1, were often less than .25 μm in size, smaller than those formed in unirradiated material and present in greater number. The results are in agreement with earlier observations on the effect of electron beam damage on Dauphiné twinning.

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