scholarly journals Proof of the elusive high-temperature incommensurate phase in CuO by spherical neutron polarimetry

2020 ◽  
Vol 6 (7) ◽  
pp. eaay7661 ◽  
Author(s):  
Navid Qureshi ◽  
Eric Ressouche ◽  
Alexander Mukhin ◽  
Marin Gospodinov ◽  
Vassil Skumryev
Keyword(s):  
High Temperature ◽  
Paraelectric Phase ◽  
Spin Hamiltonian ◽  
Spin Density Waves ◽  
Neutron Polarimetry ◽  
Peak Intensity ◽  
Structure Changes ◽  
Accidental Degeneracy ◽  
Spin Arrangement ◽  
High Transition

CuO is the only known binary multiferroic compound, and due to its high transition temperature into the multiferroic state, it has been extensively studied. In comparison to other prototype multiferroics, the nature and even the existence of the high-temperature incommensurate paraelectric phase (AF3) were strongly debated—both experimentally and theoretically—since it is stable for only a few tenths of a kelvin just below the Néel temperature. Until now, there is no proof by neutron diffraction techniques owing to its very small ordered Cu magnetic moment. Here, we demonstrate the potential of spherical neutron polarimetry, first, in detecting magnetic structure changes, which are not or weakly manifest in the peak intensity and, second, in deducing the spin arrangement of the so far hypothetic AF3 phase. Our findings suggest two coexisting spin density waves emerging from an accidental degeneracy of the respective states implying a delicate energy balance in the spin Hamiltonian.

Influence of Processing Parameters and Different Content of Tib2 Ceramics on the Properties of Composites Sintered by High Pressure -High Temperature (HP-HT) Method

2014 ◽  
Vol 59 (1) ◽  
pp. 205-209 ◽  
Author(s):  
I. Sulima ◽  
L. Jaworska ◽  
P. Figiel
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Processing Parameters ◽  
Structure Changes ◽  
High Pressure High Temperature ◽  
Mechanical And Physical Properties ◽  
Temperature And Pressure ◽  
Different Content ◽  
Scanning Electron ◽  
Properties Of Composites

Abstract In this paper the properties of the austenitic stainless steel reinforced with various volume fractions of TiB2 ceramics have been studied. The high pressure- high temperature (HP-HT) method of sintering was applied to the formation of composites. Samples were sintered at pressure of 5 and 7 ±0.2 GPa and temperatures of 1273 K and 1573 K. For the tested materials, the relative density, Young’s modulus and hardness were measured. In order to investigate the structure changes, the scanning electron microscope was used. The obtained results show that the temperature and pressure influence on the mechanical and physical properties of the investigated composites.

In situ Raman spectroscopy study on the effect of antioxidants on high temperature oxidation properties of TMPTO

2019 ◽  
Vol 71 (5) ◽  
pp. 706-711 ◽  
Author(s):  
Bingxue Cheng ◽  
Haitao Duan ◽  
Yongliang Jin ◽  
Lei Wei ◽  
Jia Dan ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
High Temperature ◽  
Thermal Oxidation ◽  
High Temperature Oxidation ◽  
Isothermal Oxidation ◽  
In Situ Raman Spectroscopy ◽  
Temperature Oxidation ◽  
Content Type ◽  
Structure Changes ◽  
Oxidation Properties

Purpose This paper aims to investigate the thermal oxidation characteristics of the unsaturated bonds (C=C) of trimethylolpropane trioleate (TMPTO) and to reveal the high temperature oxidation decay mechanism of unsaturated esters and the nature of the anti-oxidation properties of the additives. Design/methodology/approach Using a DXR laser microscopic Raman spectrometer and Linkam FTIR600 temperature control platform, the isothermal oxidation experiments of TMPTO with or without 1.0 wt. % of different antioxidants were performed. Findings The results indicated that the Raman peaks of =C-H, C=C and -CH2- weaken gradually with prolonged oxidation time, and the corresponding Raman intensities drop rapidly at higher temperatures. The aromatic amine antioxidant can decrease the attenuation of peak intensity, as it significantly reduces the rate constant of C=C thermal oxidation. The hindered phenolic antioxidant has a protective effect during the early stages of oxidation (induction period), but it may accelerate the oxidation of C=C afterwards. Originality/value Research on the structure changes of synthetic esters during oxidation by Raman spectroscopy will be of great importance in promoting the use of Raman spectroscopy to analyze the oxidation of lubricants.

Spin Arrangement of the High‐Temperature Magnetic Phase in Chromium

1965 ◽  
Vol 36 (3) ◽  
pp. 1098-1098 ◽  
Author(s):  
P. Jane Brown ◽  
C. Wilkinson ◽  
J. B. Forsyth ◽  
R. Nathans
Keyword(s):  
High Temperature ◽  
Magnetic Phase ◽  
Spin Arrangement

Powder Spectra of 51V NMR in CuV2S4: Possible Coexistence of Charge and Spin Density Waves

1996 ◽  
Vol 51 (5-6) ◽  
pp. 662-664 ◽  
Author(s):  
H. Nishihara ◽  
N. Todo ◽  
T. Hagino ◽  
S. Nagata
Keyword(s):  
High Temperature ◽  
Spin Density ◽  
Low Temperatures ◽  
Spin Echo ◽  
Density Waves ◽  
Spin Density Waves ◽  
Cubic Symmetry ◽  
Chalcogenide Spinel ◽  
Copper Chalcogenide ◽  
Lattice Distortions

Abstract NMR experiments are reported for the copper chalcogenide spinel CuV2S4 , which has incommensurate lattice distortions at low temperatures in spite of the cubic symmetry at high temperature. A broad spin-echo spectrum of 51V has been observed below 90 K at 17 MHz. but it shows a remarkable frequency dependence where it becomes sharper with decreasing frequency. Possible coexistence of charge and spin density waves is suggested at low temperatures in this material.

Superconductivity in SmFeAsO0.8F 0.2 Synthesized by High Pressure High Temperature Treatment

2011 ◽  
Vol 197-198 ◽  
pp. 499-502
Author(s):  
Zheng He Hua ◽  
Heng Zhang ◽  
Ju Peng
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Electrical Transport ◽  
Upper Critical Field ◽  
Magnetic Field Effect ◽  
Temperature Treatment ◽  
High Temperature Treatment ◽  
X Ray Diffraction ◽  
High Pressure High Temperature ◽  
High Transition

Superconducting SmFeAsO0.8F0.2 compound was successfully synthesized by high pressure high temperature treatment with pressure of 6 G Pa at 1400 °C for 2 hours. The X-ray diffraction pattern of the sample indicates the formation of the tetragonal ZrCuSiAs-type SmFeAsO0.8F0.2 with lattice parameters a=3.932 Å and c=8.490 Å. The electrical transport study shows that the sample has a rather high transition temperature Tc of about 52 K, and magnetic field effect on the resistance reveals a rather high upper critical field HC2 of about 65 T.

The Role of the Coulomb Interaction in Superconductivity

1998 ◽  
Vol 12 (29n31) ◽  
pp. 2906-2913
Author(s):  
J. D. Fan ◽  
Y. M. Malozovsky
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Scattering Amplitude ◽  
Structural Parameters ◽  
Random Phase ◽  
Particle Interaction ◽  
High Transition Temperature ◽  
Perturbation Approach ◽  
Dimensional System ◽  
High Transition

It is found that particle pairing is nothing else but grouping in the statistical sense and that only in the particle–hole channel does the BCS Hamiltonian have the BCS solution for an attractive interaction, whereas the interaction in the particle–particle channel is still repulsive. A generalized perturbation approach beyond the random phase approximation (RPA), based on Ward's identity, was developed by the authors to deal with both weakly and strongly coupled electronic systems. The full summation of all of the possible Feynman diagrams of two-particle interaction guarantees its validity. A phase transition in this method is determined by instability of the normal state, often referred to as the pairing instability, but better to resonance of interaction, equivalent to the pole condition in the two-particle scattering amplitude. Of more importance and interest is that superconductivity, regardless of low or high temperature, is found to originate from the Coulomb correlations. It was shown that only if interaction in the particle–particle channel is repulsive may the instability occur and the irreducible response function, hence conductivity, tends to infinity as temperature approaches T c . The transition temperature T c is found to be related to the physical, chemical and structural parameters, such as the dielectric constant, concentration of carriers and interlayer spacing. Therefore, low- and high-temperature superconductivity do not have an intrinsic distinction but their observed different properties. An application of the approach to a layered two-dimensional system immediately leads to the metal–superconductor (MS) transition with a possible high transition temperature, while the MS transition in an isotropic three-dimensional system can never exhibit a high transition temperature.

scholarly journals On the high temperature phase transition in Ba(Zr0.20Ti0.80)O3 ceramic

2017 ◽  
Vol 07 (04) ◽  
pp. 1750025 ◽  
Author(s):  
K. P. Chandra ◽  
A. R. Kulkarni ◽  
K. Prasad
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Lattice Structure ◽  
High Temperature Phase ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Potential Candidate ◽  
Space Group ◽  
Structure Changes ◽  
Temperature Phase Transition

Temperature dependent X-ray diffraction (XRD) and dielectric properties of perovskite Ba(Zr[Formula: see text]Ti[Formula: see text]O3 ceramic prepared using a standard solid-state reaction process is presented. Along with phase transitions at low temperature, a new phase transition at high temperature (873[Formula: see text]C at 20[Formula: see text]Hz), diffusive in character has been found where the lattice structure changes from monoclinic (space group: [Formula: see text] to hexagonal (space group: [Formula: see text]). This result places present ceramic in the list of potential candidate for intended high temperature applications. The AC conductivity data followed hopping type charge conduction and supports jump relaxation model. The experimental value of [Formula: see text][Formula: see text]pC/N was found. The dependence of polarization and strain on electric field at room temperature suggested that lead-free Ba(Zr[Formula: see text]Ti[Formula: see text]O3 is a promising material for electrostrictive applications.

The Influence of Dy3+ in the Novel Electron Trapping Materials (ETM) (ETM) SrS: Eu2+, Dy3+

2010 ◽  
Vol 663-665 ◽  
pp. 429-433
Author(s):  
Jia Yue Sun ◽  
Zhen Xing Liu ◽  
Hai Yan Du
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Visible Light ◽  
Solid State Reaction ◽  
Emission Peak ◽  
Electron Trapping ◽  
The Novel ◽  
Peak Intensity ◽  
Broadband Spectrum ◽  
Exciting Source

A new electron trapping materials (ETM) SrS: Eu2+, Dy3+, which was prepared by the method of high temperature solid-state reaction. The results indicate that both ultraviolet light and visible light can be used as exciting source to store energy. After exposed under ultraviolet, the sample was stimulated by 980nm laser. As a result, an obvious luminescence at 615 nm was detected. The up-conversion emission spectrum was found to be a continuous broadband spectrum resulted from the multi-transitions of Eu2+ 4f6→4f7 (8S7/2). The emission peak intensity of SrS: Eu2+, Dy3+ was stronger than SrS: Eu2+.

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