scholarly journals Fеatures of exchange interactions of the B-sublattice ions in the La0,5Sr0,5Co1–x Nix O3–d system

2021 ◽  
Vol 65 (5) ◽  
pp. 539-545
Author(s):  
R. A. Lanovsky ◽  
A. V. Nikitsin ◽  
M. V. Bushinsky ◽  
N. V. Tereshko ◽  
O. S. Mantytskaya ◽  
...  
Keyword(s):  
Spin State ◽  
Magnetic Transition ◽  
Exchange Interactions ◽  
High Spin State ◽  
Unit Cell ◽  
Ferromagnetic Phase ◽  
National Academy Of Sciences ◽  
Cell Parameters ◽  
Ferromagnetic Interactions ◽  
The Stability

A comprehensive study of the crystal structure, magnetic and magnetotransport properties of the La0.5Sr0.5Co1–x Nix O3–d  cobaltite system (x = 0.1–0.16) was carried out. The X-ray measurement results indicate that the unit cell of all solid solutions of the system is cubic and is described by the space group Pm3m. It is found that with an increase in the 540     Doklady of the National Academy of Sciences of Belarus, 2021, vol. 65, no. 5, рр. 539–545 Ni content, the Curie temperature (TC) decreases from 230 to 180 K, as well as magnetization values. The magnetic transition is blurred across the field. The iodometric studies show that the concentration of Co4+ ions in all samples does not exceed 35 %. The chemical substitution of Co ions by Ni ones does not result in significant modification of the unit cell parameters, which may indicate a spin crossover of Co ions. The temperature dependence of resistivity is metallic in character, which indicates the stability of the main conducting ferromagnetic phase. The nature of exchange interactions of different signs between B-sublattice ions completely determines the behavior of the system. An increase in the content of Ni ions leads both to decrease the component of ferromagnetic exchange interactions between Co3+ ions in the intermediate spin state and to increase the fraction of antiferromagnetic and weaker ferromagnetic interactions. In addition, presumably the Co4+ ion can stabilize the high spin state of the closestCo3+ ion and in the next two coordination spheres it can stabilize the Co3+ ion in the low spin state, i. e. the ferromagnetic complexes Co4+–Co3+ (HS) are shielded by the diamagnetic shell of low spin Co3+ ions, which results in decreasing the magnetization values.

Stability of High-Spin State of Iron in β-NaFeO2

2020 ◽  
Vol 855 ◽  
pp. 177-182
Author(s):  
Mochammad Yan Pandu Akbar ◽  
Rieko Ishii ◽  
Agustinus Agung Nugroho
Keyword(s):  
Single Crystal ◽  
High Spin ◽  
Spin State ◽  
High Spin State ◽  
Polycrystalline Sample ◽  
Single Crystal Sample ◽  
Structural Refinement ◽  
Crystal Sample ◽  
The Stability ◽  
Crystal Volume

We investigated the stability of the high-spin state of the iron β-NaFeO2 based on the structural refinement. The oxidation of the Fe2+ ion in the as-synthesized sample is evidenced by its green color. Due to its sensitivity in air and CO2, this compound will decompose into a reddish Fe3+ state. The smaller crystal volume of the decomposed compound is mainly related to the shorter ionic radius of the high-spin state Fe3+ and this result will be compared to the single crystal sample. In contrast to the polycrystalline sample, the decomposition single crystal sample only taking place on the surface of the as-grown crystal.

scholarly journals Crystallographic and DFT Studies on Pyrrolo[1,2-c]imidazole Scaffolds

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Manikandan Jayaraman ◽  
Rajarathinam Balakrishnan ◽  
Kannan Muthu ◽  
Manivel Panneerselvam ◽  
Vasuki Gnanasambandam ◽  
...  
Keyword(s):  
Density Functional ◽  
Crystal Packing ◽  
Stable State ◽  
Chair Conformation ◽  
Unit Cell ◽  
Basis Set ◽  
Monoclinic Space Group ◽  
Cell Parameters ◽  
B3lyp Method ◽  
The Stability

The crystal structures of the compounds C15H14N4O2 (1) and C16H16N4O4 (2) are reported and analyzed by single crystal X-ray diffraction technique. Compounds (1) and (2) crystallized in monoclinic space group P21/c and Cc with four molecules in the unit cell, respectively. The unit cell parameters for compound (1) are a = 11.4501(15) Å, b = 9.7869(11) Å, c = 12.3653(15) Å, β = 90.997(11)°, and Volume = 1385.5(3) Å3 and for compound (2) are a = 13.865(2) Å, b = 6.9538(8) Å, c = 16.841(2) Å, β = 98.602(11)°, and Volume = 1605.4(4) Å3. In both compounds (1) and (2), the pyrrolidine ring adopts half-chair conformation. Moreover, both inter- and intramolecular N–H⋯O hydrogen bonds stabilize the crystal structure and play a crucial role in crystal packing. This intermolecular interaction alone constructs C11 chain motif in both compounds. It is also supported by weak intermolecular π-π interaction which is essential for the stability of the crystal packing. Further, the Density Functional Theory (B3LYP) method with standard 6-31G basis set was used in the calculation and calculated geometrical parameter is correlated with the corresponding experimental data. The obtained HOMO and LUMO energies are in negative values indicating that the compounds are in stable state.

Phase identification and superconductivity transitions in Sr-doped Pr1.85Ce0.15CuO4+δ

1997 ◽  
Vol 12 (10) ◽  
pp. 2526-2532 ◽  
Author(s):  
A. Varela ◽  
M. Vallet-Regí ◽  
J. M. González-Calbet
Keyword(s):  
Electron Diffraction ◽  
Diffraction Study ◽  
Oxygen Content ◽  
Electron Diffraction Study ◽  
Unit Cell ◽  
Hole Doping ◽  
Phase Identification ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
The Stability

Sr-doped Pr1.85Ce0.15CuO4+δ samples have been prepared with accurate control of the oxygen content. The stability of both T′ and T* phases is strongly dependent on Sr and oxygen content. An electron diffraction study indicates that, in some cases, anionic vacancies are ordered leading to a pseudo-tetragonal superlattice with unit cell parameters . Structural transitions and superconducting phases created by hole doping in such a system are also reported.

X-ray powder diffraction study of the stability of solid solutions in (La1−xGdx)OCl

1996 ◽  
Vol 11 (2) ◽  
pp. 129-133 ◽  
Author(s):  
Jorma Hölsä ◽  
Eija Säilynoja ◽  
Kari Koski ◽  
Hanna Rahiala ◽  
Jussi Valkonen
Keyword(s):  
Powder Diffraction ◽  
Solid Solutions ◽  
Valence Bond ◽  
Unit Cell ◽  
X Ray ◽  
Cell Parameters ◽  
Local Distortion ◽  
Gaussian Profile ◽  
Bond Model ◽  
The Stability

The formation of the solid solutions in the (La1−xGdx)OCl series was studied by X-ray powder diffraction (XPD) at room temperature in the 2θ region between 6.5 and 120°. The Rietveld profile refinement analyses of the XPD patterns were carried out with the background, unit cell, atomic position, isotropic temperature, and Gaussian profile form parameters refined freely. All (La1−xGdx)OCl samples possessed the tetragonal PbFCl-type structure with P4/nmm as the space group (Z=2). The unit cell parameters a and c evolve smoothly through the series and no clustering of the Gd3+ ions was observed according to Vegard's law. The solid solubility exists throughout the whole series. The valence bond model was used to estimate the relative stabilities of the different (La1−xGdx)OCl solid solutions. The global instability index (GII) which equals to the deviation between the formal valence and the sum of the calculated valence bonds of each atom in the asymmetric unit was used as a tool in the assessment. In the (La1−xGdx)OCl series, GII increases both from the end and the beginning of the series toward the middle indicating diminishing stability. No breakdown of the La–Gd solid solution could be verified experimentally although the GII value for the (La0.4Gd0.6)OCl composition exceeds the limit of 0.2 which should mean the collapse of the structure. However, the diffraction reflections were found somewhat broader in the middle of the series indicating possible local distortion or disorder.

scholarly journals Zeroth-Order Nucleation Transition under Nanoscale Phase Separation

Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2379
Author(s):  
Vyacheslav I. Yukalov ◽  
Elizaveta P. Yukalova
Keyword(s):  
Phase Separation ◽  
Stable State ◽  
Exchange Interactions ◽  
Ferromagnetic State ◽  
Ferromagnetic Phase ◽  
Zeroth Order ◽  
Nanoscale Phase Separation ◽  
Finite Concentration ◽  
Coexisting Phases ◽  
The Stability

Materials with nanoscale phase separation are considered. A system representing a heterophase mixture of ferromagnetic and paramagnetic phases is studied. After averaging over phase configurations, a renormalized Hamiltonian is derived describing the coexisting phases. The system is characterized by direct and exchange interactions and an external magnetic field. The properties of the system are studied numerically. The stability conditions define the stable state of the system. At a temperature of zero, the system is in a pure ferromagnetic state. However, at finite temperature, for some interaction parameters, the system can exhibit a zeroth-order nucleation transition between the pure ferromagnetic phase and the mixed state with coexisting ferromagnetic and paramagnetic phases. At the nucleation transition, the finite concentration of the paramagnetic phase appears via a jump.

Kinematical and Dynamical CBED Pattern Models: Increasing the Accuracy of the Unit-Cell Parameter Measurements Based on CBED Patterns

1990 ◽  
Vol 48 (2) ◽  
pp. 540-541
Author(s):  
I.N. Yadhikov ◽  
S.K. Maksimov
Keyword(s):  
Reciprocal Lattice ◽  
Unit Cell ◽  
Reciprocal Lattice Vector ◽  
Unit Cell Parameters ◽  
Lattice Vector ◽  
Cell Parameters ◽  
Accuracy Of Measurements ◽  
The Difference ◽  
Image Position ◽  
Convergent Beam

Convergent beam electron diffraction (CBED) is widely used as a microanalysis tool. By the relative position of HOLZ-lines (Higher Order Laue Zone) in CBED-patterns one can determine the unit cell parameters with a high accuracy up to 0.1%. For this purpose, maps of HOLZ-lines are simulated with the help of a computer so that the best matching of maps with experimental CBED-pattern should be reached. In maps, HOLZ-lines are approximated, as a rule, by straight lines. The actual HOLZ-lines, however, are different from the straights. If we decrease accelerating voltage, the difference is increased and, thus, the accuracy of the unit cell parameters determination by the method becomes lower.To improve the accuracy of measurements it is necessary to give up the HOLZ-lines substitution by the straights. According to the kinematical theory a HOLZ-line is merely a fragment of ellipse arc described by the parametric equationwith arc corresponding to change of β parameter from -90° to +90°, wherevector, h - the distance between Laue zones, g - the value of the reciprocal lattice vector, g‖ - the value of the reciprocal lattice vector projection on zero Laue zone.

Sectioned rubisco crystals in TEM

1990 ◽  
Vol 48 (3) ◽  
pp. 664-665
Author(s):  
Gunnel Karlsson ◽  
Jan-Olov Bovin ◽  
Michael Bosma
Keyword(s):  
Plant Cell ◽  
Carbon Fixation ◽  
Unit Cell ◽  
Protein Crystals ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Photosynthetic Carbon Fixation ◽  
Photosynthetic Carbon

RuBisCO (D-ribulose-l,5-biphosphate carboxylase/oxygenase) is the most aboundant enzyme in the plant cell and it catalyses the key carboxylation reaction of photosynthetic carbon fixation, but also the competing oxygenase reaction of photorespiation. In vitro crystallized RuBisCO has been studied earlier but this investigation concerns in vivo existance of RuBisCO crystals in anthers and leaves ofsugarbeets. For the identification of in vivo protein crystals it is important to be able to determinethe unit cell of cytochemically identified crystals in the same image. In order to obtain the best combination of optimal contrast and resolution we have studied different staining and electron accelerating voltages. It is known that embedding and sectioning can cause deformation and obscure the unit cell parameters.

On the accuracy of determining the unit cell parameters of single crystals on modern laboratory diffractometers

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
П.C. Серебренникова ◽  
В.Ю. Комаров ◽  
А.С. Сухих ◽  
С.А. Громилов
Keyword(s):  
Single Crystals ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Cell Parameters

scholarly journals Allanite at high temperature: effect of REE on the thermal behaviour of epidote-group minerals

2021 ◽  
Vol 48 (9) ◽  
Author(s):  
G. Diego Gatta ◽  
Francesco Pagliaro ◽  
Paolo Lotti ◽  
Alessandro Guastoni ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Cell Volume ◽  
Thermal Behaviour ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Atomic Scale ◽  
Elastic Behaviour ◽  
Positive Trend ◽  
Cell Parameters ◽  
Thermal Anisotropy ◽  
Different Temperatures

AbstractThe thermal behaviour of a natural allanite-(Ce) has been investigated up to 1073 K (at room pressure) by means of in situ synchrotron powder X-ray diffraction and single-crystal neutron diffraction. Allanite preserves its crystallinity up to 1073 K. However, up to 700 K, the thermal behaviour along the three principal crystallographic axes, of the monoclinic β angle and of the unit-cell volume follow monotonically increasing trends, which are almost linear. At T > 700–800 K, a drastic change takes place: an inversion of the trend is observed along the a and b axes (more pronounced along b) and for the monoclinic β angle; in contrast, an anomalous increase of the expansion is observed along the c axis, which controls the positive trend experienced by the unit-cell volume at T > 700–800 K. Data collected back to room T, after the HT experiments, show unit-cell parameters significantly different with respect to those previously measured at 293 K: allanite responds with an ideal elastic behaviour up to 700 K, and at T > 700–800 K its behaviour deviates from the elasticity field. The thermo-elastic behaviour up to 700 K was modelled with a modified Holland–Powell EoS; for the unit-cell volume, we obtained the following parameters: VT0 = 467.33(6) Å3 and αT0(V) = 2.8(3) × 10–5 K−1. The thermal anisotropy, derived on the basis of the axial expansion along the three main crystallographic directions, is the following: αT0(a):αT0(b):αT0(c) = 1.08:1:1.36. The T-induced mechanisms, at the atomic scale, are described on the basis of the neutron structure refinements at different temperatures. Evidence of dehydroxylation effect at T ≥ 848 K are reported. A comparison between the thermal behaviour of allanite, epidote and clinozoisite is carried out.

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