Deformations of the α-Fe2O3 rhombohedral lattice across the Néel temperature

High-resolution synchrotron radiation powder diffraction patterns of α-Fe2O3 measured between room temperature and 1100 K, i.e. above the Néel temperature T N = 950 K, have been analyzed. The integral breadths of the Bragg peaks show a hkl-dependent anisotropy, both below and above T N. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). J. Appl. Cryst. 32, 281]. Model calculations show that the rhombohedral α-Fe2O3 lattice is deformed and the deformation leads to a monoclinic lattice with the unique monoclinic axis along the hexagonal [110] direction both below and above T N. The monoclinic symmetry of bulk α-Fe2O3 is compatible with α-Fe2O3 nanowire growth along the [110] direction reported in Fu et al. [Chem. Phys. Lett. (2001), 350, 491].

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Conduction Characteristics of Charge Ordering Type Ferroelectrics,YFe2O4

MRS Proceedings ◽

10.1557/proc-0966-t07-27 ◽

2006 ◽

Vol 966 ◽

Author(s):

Ken Imamura ◽

Yoichi Horibe ◽

Takeshi Yoshimura ◽

Norifumi Fujimura ◽

Shigeo Mori ◽

...

Keyword(s):

Room Temperature ◽

Inflection Point ◽

Oxygen Deficiency ◽

Complex Impedance ◽

Charge Ordering ◽

Neel Temperature ◽

Ohmic Conduction ◽

Néel Temperature ◽

Impedance Measurements ◽

Conduction Properties

ABSTRACTElectrical conduction properties of charge ordering type ferroelectrics YFe2O4 were investigated. YFe2O4 was synthesized in reduced atmosphere at 1200 °C. Oxygen partial pressure of the reduced atmosphere was controlled by the equilibrium state of CO and CO2. YFe2O4 is paramagnetic at room temperature and has Néel temperature around 250K. The Néel temperature was decreased with increasing the amount of oxygen deficiency. Moreover, YFe2O4 showed ohmic conduction from 260 to 100 K. The temperature dependence of the DC conductivity showed an inflection point at the Néel temperature, which indicated the development of charge ordering of Fe2+ and Fe3+ ions. From the complex impedance measurements, the equivalent circuits of YFe2O4 with different oxygen deficiency were determined at various temperatures.

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Two-dimensional C12Mn2/C12Cr2 as a room-temperature half metal/antiferromagnetic semiconductor: a systematic study

Physical Chemistry Chemical Physics ◽

10.1039/c6cp07374c ◽

2017 ◽

Vol 19 (4) ◽

pp. 3394-3404 ◽

Cited By ~ 2

Author(s):

Zheng-Zhe Lin

Keyword(s):

Systematic Study ◽

Room Temperature ◽

Neel Temperature ◽

Two Dimensional ◽

Néel Temperature ◽

Half Metal

Two-dimensional C12Mn2/C12Cr2 as a half metal/antiferromagnetic semiconductor with high Curie/Néel temperature.

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Magneto-dielectric anomaly in (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3 electroceramic

MRS Proceedings ◽

10.1557/opl.2014.146 ◽

2014 ◽

Vol 1636 ◽

Cited By ~ 2

Author(s):

Shalini Kumari ◽

Nora Ortega ◽

Ashok Kumar ◽

Ram S. Katiyar

Keyword(s):

Dielectric Response ◽

Analytical Data ◽

Rhombohedral Phase ◽

Dielectric Anomaly ◽

Neel Temperature ◽

X Ray Diffraction ◽

Néel Temperature ◽

Conventional Solid State Reaction ◽

Diffraction Patterns ◽

Small Chemical

ABSTRACTWe report magneto-dielectric anomaly of the multiferroic (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3 (BNFM) ceramic near Néel temperature. The ceramic pellets were synthesized by conventional solid state reaction route. X-ray diffraction patterns revealed that most of the peaks shifted slightly towards higher Bragg’s angle compared to those of pure BiFeO3 and also confirmed the formation of rhombohedral phase. It also suggests that the small chemical substitution of Nd and Mn atoms at Bi and Fe sites of BiFeO3 (BFO) perovskite respectively does not alter the crystal structure. Temperature and frequency dependent dielectric response indicate large dielectric anomaly at 620 K, slightly below the known Néel temperature of BFO. The enhancement in dielectric properties of BNFM ceramic was observed as compared to BFO due to suppression of oxygen vacancies by the doping. Temperature dependent dielectric response in conjunction with Raman and thermo-analytical data show that the BNFM sample presents significant magneto-dielectric response around Néel temperture TN ∼ 620 K.

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X-ray powder diffraction data and thermal expansion of N(CH3)4Br and N(CH3)4I

Powder Diffraction ◽

10.1017/s0885715600009192 ◽

1996 ◽

Vol 11 (3) ◽

pp. 246-249 ◽

Cited By ~ 2

Author(s):

Alex Xenopoulos ◽

Martina Ralle ◽

Anton Habenschuss ◽

Bernhard Wunderlich

Keyword(s):

Thermal Expansion ◽

Powder Diffraction ◽

Room Temperature ◽

Chem Phys ◽

Powder Diffraction Data ◽

Unit Cell Parameters ◽

X Ray ◽

Cell Parameters ◽

Tetramethylammonium Bromide ◽

Diffraction Patterns

The X-ray powder diffraction patterns for tetramethylammonium bromide and iodide have been measured from near room temperature up to decomposition/sublimation. The unit cell parameters were refined and the coefficients of thermal expansion calculated. Unlike N(CH3)4Cl [M. Stammler, J. Inorg. Nucl. Chem. 29, 2203–2221 (1967)], N(CH3)4Br (1Br) and N(CH3)4I (1I) undergo no solid–solid transitions before decomposition/sublimation as was observed earlier by thermal analysis [S. S. Chang and E. F. Westrum, J. Chem. Phys. 36(9), 2420–2423 (1962); Coulter etal., J. Am. Chem. Soc. 62, 2845–2851 (1940); Xenopoulos etal., Mol. Cryst. Liq. Cryst. 214, 63–79 (1992)].

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Sintering Temperature Dependent Permeability of Nanocrystalline Ni0.20Cu0.30Zn0.50Fe2O4 Ferrite

Journal of Bangladesh Academy of Sciences ◽

10.3329/jbas.v35i1.7972 ◽

2011 ◽

Vol 35 (1) ◽

pp. 67-75 ◽

Cited By ~ 1

Author(s):

ML Rahman ◽

MHR Khan ◽

ST Mahmud ◽

AKM Akther Hossain

Keyword(s):

Room Temperature ◽

Sintering Temperature ◽

Spinel Ferrite ◽

Magnetization Measurement ◽

Initial Permeability ◽

Neel Temperature ◽

Néel Temperature ◽

Dc Magnetization ◽

Average Grain Size ◽

Auto Combustion

The spinel ferrite of Ni0.20Cu0.30Zn0.50Fe2O4 was studied at room temperature using X-ray diffraction pattern prepared by auto combustion technique. The analysis of the XRD patterns showed that the sample has a single phase cubic spinel structure. The bulk density, average grain size and initial permeability increase with increasing sintering temperature up to a optimum temperature. Beyond that temperature all those properties decreases. The value of relative quality factor decreases with increasing sintering temperature. The DC magnetization measurement showed that at room temperature the sample is in ferrimagnetic state. The number of Bohr magneton, n(?B), Néel temperature, TN, and the field at which saturation occurs were also calculated and possible explanation for the observed characteristics of microstructure, initial permeability, DC magnetization, and Néel temperature of the studied sample are presented.DOI: http://dx.doi.org/10.3329/jbas.v35i1.7972Journal of Bangladesh Academy of Sciences, Vol.35, No.1, 67-75, 2011

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Otoconia perfect/imperfect crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167949 ◽

1994 ◽

Vol 52 ◽

pp. 42-43

Author(s):

César D. Fermin ◽

Dale Martin

Keyword(s):

Image Processing ◽

Room Temperature ◽

Phosphotungstic Acid ◽

Gallus Domesticus ◽

Crystal Matrix ◽

Organic Templates ◽

Image Processing Algorithms ◽

Processing Algorithms ◽

Diffraction Patterns

Otoconia of higher vertebrates are interesting biological crystals that display the diffraction patterns of perfect crystals (e.g., calcite for birds and mammal) when intact, but fail to produce a regular crystallographic pattern when fixed. Image processing of the fixed crystal matrix, which resembles the organic templates of teeth and bone, failed to clarify a paradox of biomineralization described by Mann. Recently, we suggested that inner ear otoconia crystals contain growth plates that run in different directions, and that the arrangement of the plates may contribute to the turning angles seen at the hexagonal faces of the crystals.Using image processing algorithms described earlier, and Fourier Transform function (2FFT) of BioScan Optimas®, we evaluated the patterns in the packing of the otoconia fibrils of newly hatched chicks (Gallus domesticus) inner ears. Animals were fixed in situ by perfusion of 1% phosphotungstic acid (PTA) at room temperature through the left ventricle, after intraperitoneal Nembutal (35mg/Kg) deep anesthesia. Negatives were made with a Hitachi H-7100 TEM at 50K-400K magnifications. The negatives were then placed on a light box, where images were filtered and transferred to a 35 mm camera as described.

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STEM and ELS Observation of Early Oxide Formation on the Surface of Cr Thin Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600001768 ◽

1980 ◽

Vol 38 ◽

pp. 412-413

Author(s):

Fumio Watari ◽

J. M. Cowley

Keyword(s):

Thin Films ◽

Optical System ◽

Room Temperature ◽

Oxide Formation ◽

Initial Nucleation ◽

Diffraction Patterns ◽

Relationship Of ◽

Multiple Twinning ◽

Moderately High Temperature

STEM coupled with the optical system was used for the investigation of the early oxidation on the surface of Cr. Cr thin films (30 – 1000Å) were prepared by evaporation onto the polished or air-cleaved NaCl substrates at room temperature and 45°C in a vacuum of 10−6 Torr with an evaporation speed 0.3Å/sec. Rather thick specimens (200 – 1000Å) with various preferred orientations were used for the investigation of the oxidation at moderately high temperature (600 − 1100°C). Selected area diffraction patterns in these specimens are usually very much complicated by the existence of the different kinds of oxides and their multiple twinning. The determination of the epitaxial orientation relationship of the oxides formed on the Cr surface was made possible by intensive use of the optical system and microdiffraction techniques. Prior to the formation of the known rhombohedral Cr2O3, a thin spinel oxide, probably analogous to γ -Al203 or γ -Fe203, was formed. Fig. 1a shows the distinct epitaxial growth of the spinel (001) as well as the rhombohedral (125) on the well-oriented Cr(001) surface. In the case of the Cr specimen with the (001) preferred orientation (Fig. 1b), the rings explainable by spinel structure appeared as well as the well defined epitaxial spots of the spinel (001). The microdif fraction from 20A areas (Fig. 2a) clearly shows the same pattern as Fig. Ia with the weaker oxide spots among the more intense Cr spots, indicating that the thickness of the oxide is much less than that of Cr. The rhombohedral Cr2O3 was nucleated preferably at the Cr(011) sites provided by the polycrystalline nature of the present specimens with the relation Cr2O3 (001)//Cr(011), and by further oxidation it grew into full coverage of the rest of the Cr surface with the orientation determined by the initial nucleation.

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