Anomalies of the Fast Relaxation Dynamics at Tg In Strong Glass Formers

1996 ◽  
Vol 455 ◽  
Author(s):  
A. Brodin ◽  
L. M. Torell
Keyword(s):  
Mode Coupling ◽  
Integral Intensity ◽  
Relaxation Dynamics ◽  
Quasielastic Scattering ◽  
Temperature Dependent ◽  
Heat Temperature ◽  
System A ◽  
Fast Relaxation ◽  
Temperature Dependences ◽  
Limiting Value

ABSTRACTStructural dynamics of two network forming glasses, B2O3 and GeO2, has been investigated by Raman scattering over a wide temperature range from ∼10 K to above the respective glass transition temperatures (Tg = 526 K for B2O3 and 800 K for GeO2). The spectra are analyzed in terms of two distinct contributions, related to vibrational and fast relaxational dynamics, respectively, and conventionally referred to as the boson peak (BP) and quasielastic scattering (QS). A quantity proportional to the fast relaxation strength may be deduced from the integral intensity of QS relative to BP of the spectra. It turns out, that for T < Tg the so-obtained QS intensity of the two glasses is similar and smoothly temperature dependent, and can qualitatively be described by e.g. the defect model or the soft potential model. As Tg is passed, there is a pronounced change in behavior and dramatic differences between the two systems are observed. Thus, the fast relaxational dynamics is obviously affected by Tg, a finding which is in contrast to the predictions of the mode coupling theory (MCT) of a single crossover temperature Tc > Tg. Moreover, the experimentally obtained value of the MCT exponent a, describing the shape of the fast dynamics, is by far exceeding the limiting value (a ≈ 0.395) of the theory, the deviation increasing with the strength of the system (a ≈ 0.7 for B2O3 and ≈ 0.9 for GeO2). The observed difference between the two glasses is discussed in terms of the fragility of the system manifested in jumps in the specific heat temperature dependences.

Emergence of size induced metallic state in the ferromagnetic insulating Pr0.8Sr0.2MnO3 manganite: Breaking of surface polarons

2015 ◽  
Vol 8 (2) ◽  
pp. 2084-2093 ◽  
Author(s):  
PROLOY TARAN DAS ◽  
Arun Kumar Nigam ◽  
Tapan Kumar Nath
Keyword(s):  
Transport Properties ◽  
Metallic State ◽  
Temperature Dependent ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
System A ◽  
Surface Disorder ◽  
Bulk System ◽  
Magnetic Transport ◽  
Grain Surface

Nano-dimensional effects on electronic-, magneto-transport properties of granular ferromagnetic insulating (FMI) Pr0.8Sr0.2MnO3 (PSMO) manganite (down to 40 nm) have been investigated in details. From the electronic and magnetic transport properties, a metallic state has been observed in grain size modulation by suppressing the ferromagnetic insulating state of PSMO bulk system. A distinct metal-insulator transition (MIT) temperature around 150 K has been observed in all nanometric samples. The observed insulator to metallic transition with size reduction can be explained with surface polaron breaking model, originates due to enhanced grain surface disorder. This proposed phenomenological polaronic model plays a significant role to understand the polaronic destabilization process on the grain surface regime of these phase separated nano-mangnatie systems. Temperature dependent resistivity and magnetoresistance data in presence of external magnetic fields are investigated in details with various compatible models.

"Double-W-shaped" temperature dependence of emission linewidth in an InGaN/GaN multiple quantum well structure with intense phase separation

2020 ◽  
Vol 10 (1) ◽  
pp. 140-144
Author(s):  
Changfu Li ◽  
Mingsheng Xu ◽  
Ziwu Ji ◽  
Kaiju Shi ◽  
Hongbin Li ◽  
...  
Keyword(s):  
Phase Separation ◽  
Temperature Dependence ◽  
Multiple Quantum Well ◽  
Excitation Power ◽  
Multiple Quantum ◽  
Temperature Dependent ◽  
Two Phase ◽  
Phase Structures ◽  
Temperature Dependences ◽  
Lower Excitation

The temperature dependence of the spectra of photoluminescence (PL) from a blue InGaN/GaN multiplequantum-well (MQW) structure is investigated at lower excitation power. Two emission peaks, related to InGaN and assigned to In-rich quasi-quantum dots (QDs) and InGaN-matrix in the full PL spectrum, were observed. Upon increasing the temperature, both PL peak linewidths exhibited "double-W-shaped" (narrowing–broadening–narrowing–broadening–narrowing–broadening) temperature dependence. Combined with the observed features of the temperature dependences of the PL intensities, the temperature-dependent behaviors in this case can be interpreted as the relaxation and thermalization of carriers inside respective phase structures and the transfer of carriers between two phase structures, because of the strong phase separation and significant component fluctuation in the InGaN well layers.

Dynamic behavior and strategy for the complete 1H and 13C assignments for meso-aryl expanded heptaphyrins

2002 ◽  
Vol 06 (06) ◽  
pp. 410-422 ◽  
Author(s):  
Bhawani S. Joshi ◽  
Venkataramanarao G. Anand ◽  
Simi K. Pushpan ◽  
Alagar Srinivasan ◽  
Tavarekere K. Chandrashekar ◽  
...  
Keyword(s):  
Dynamic Behavior ◽  
Intramolecular Hydrogen Bonding ◽  
Native State ◽  
Temperature Dependent ◽  
System A ◽  
Expanded Porphyrins ◽  
Nmr Techniques ◽  
Intramolecular Hydrogen ◽  
C Nmr

The detailed 1 H and 13 C NMR analysis of 5,10,19,24-tetramesityl-33,35,36,38,39-pentathiaheptaphyrin (1) and 5,10,19,24-tetraphenyl-35,36-dioxa-33,38,39-trithiaheptaphyrin (2) in the native and protonated state were carried out using two-dimensional NMR techniques. The analysis suggests that the earlier reported structure containing inverted terminal thiophene of trithiophene should be corrected as the inverted thiophene and furan of bithiophene and bifuran instead of trithiophene system of 1 and 2, respectively. Temperature dependent and titration studies suggest that 1 is less flexible in the native state then 2 due to presence of the mesityl group despite having disorder due to the presence of the heavier sulphur atom. This was consequently proven by the NMR information obtained in 5,10,19,24-tetramesityl-35,36-dioxa-33,38,39-trithiaheptaphyrin (3). Whereas in its protonated state, 2 was found to be less flexible than 1 due to presence of intramolecular hydrogen bonding involving N - H --- O between the pyrrole NH and oxygen of the furan of bifuran system. A systematic NMR strategy has been generated in order to provide complete a structure determination of expanded porphyrins along with their dynamic behavior.

First-Principles Investigation of Phase Stability, Elastic and Thermodynamic Properties in L12 Co3(Al,Mo,Ta) Phase

2017 ◽  
Vol 898 ◽  
pp. 438-445
Author(s):  
Qiang Yao ◽  
Tong Lu ◽  
Qiong Wang ◽  
Yan Wang ◽  
Yu Hong Zhu
Keyword(s):  
Thermodynamic Properties ◽  
Phase Stability ◽  
First Principles ◽  
Linear Thermal Expansion ◽  
Temperature Dependent ◽  
Shear Moduli ◽  
Young’S Moduli ◽  
High Temperature Alloys ◽  
Temperature Dependences ◽  
Significant Temperature

First-principles calculations have been performed to investigate the phase stability, elastic, and thermodynamic properties of Co3(Al,Mo,Ta) with the L12 structure. Calculated elastic constants showed that Co3(Al,Mo,Ta) is mechanically stable and possesses intrinsic ductility. Young’s and shear moduli of polycrystalline Co3(Al,Mo,Ta) were calculated using the Voigt-Reuss-Hill approach. It was found that the shear and Young’s moduli of Co3(Al,Mo,Ta) were smaller than those of Co3(Al,W). States density indicated the existence of covalent-like bonding in Co3(Al,Mo,Ta). Temperature-dependent thermodynamic properties of Co3(Al,Mo,Ta) could be described satisfactorily using the Debye-Grüneisen approach, including entropy, enthalpy, heat capacity and linear thermal expansion coefficient, showing their significant temperature dependences. Furthermore the obtained data could be employed in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys.

Kinetic paths of B2 and DO3 order parameters: Experiment

1989 ◽  
Vol 4 (5) ◽  
pp. 1140-1142 ◽  
Author(s):  
L. Anthony ◽  
B. Fultz
Keyword(s):  
Thermal Equilibrium ◽  
Nearest Neighbor ◽  
Order Parameters ◽  
Temperature Dependent ◽  
Critical Temperatures ◽  
Subsequent Evolution ◽  
X Ray ◽  
Rates Of Change ◽  
Temperature Dependences ◽  
Different Temperatures

Rapidly quenched powders of Fe3Al were subjected to thermal annealings at temperatures well below the critical temperatures for B2 and DO3 ordering. X-ray diffractometry was used to measure the subsequent evolution of B2 and DO3 long-range order. It was found that the relative rates of change of B2 and DO3 order parameters were temperature dependent; hence at different temperatures the alloy passed through different states of order en route to thermal equilibrium. These temperature dependences of “kinetic paths” can be understood in terms of a theory of kinetic paths based on the kinetic master equation. The theory indicates that the temperature dependence of the observed kinetic paths originates from having first-nearest-neighbor interactions that are stronger than second-nearest-neighbor interactions. This seems consistent with previous thermodynamic analyses of critical temperatures of Fe3Al.

Bright two-photon emission and ultra-fast relaxation dynamics in a DNA-templated nanocluster investigated by ultra-fast spectroscopy

Nanoscale ◽  
2012 ◽  
Vol 4 (14) ◽  
pp. 4247 ◽  
Author(s):  
Sung Hei Yau ◽  
Neranga Abeyasinghe ◽  
Meghan Orr ◽  
Leslie Upton ◽  
Oleg Varnavski ◽  
...  
Keyword(s):  
Photon Emission ◽  
Relaxation Dynamics ◽  
Two Photon ◽  
Fast Relaxation

Fast Relaxation Dynamics of the Cardiotonic Drug Milrinone in Water Solutions

2006 ◽  
Vol 49 (11) ◽  
pp. 3086-3091 ◽  
Author(s):  
Maged El-Kemary ◽  
Juan Angel Organero ◽  
Abderrazzak Douhal
Keyword(s):  
Relaxation Dynamics ◽  
Water Solutions ◽  
Fast Relaxation ◽  
Cardiotonic Drug

Dielectric properties of (NH4)2SO4 crystals in the range of electronic excitations

2009 ◽  
Vol 16 (2) ◽  
pp. 260-263 ◽  
Author(s):  
B. Andriyevsky ◽  
C. Cobet ◽  
A. Patryn ◽  
N. Esser
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Dielectric Properties ◽  
Large Temperature ◽  
Electronic Excitations ◽  
Temperature Dependent ◽  
Temperature Changes ◽  
The Real ◽  
Temperature Dependences ◽  
Simultaneous Decrease

Spectra of the real and imaginary parts of the pseudo-dielectric permittivity, 〈∊1〉(E) and 〈∊2〉(E), of ferroelectric ammonium sulfate crystals, (NH4)2SO4, have been measured in the range of electronic excitations 4.0 to 9.5 eV by ellipsometry using synchrotron radiation. Temperature dependences of the corresponding susceptibilities, 〈χ1〉(T) and 〈χ2〉(T), obtained for the photon energy E = 8.5 eV, related to excitations of oxygen p-electrons, reveal sharp peak-like temperature changes near the Curie point T C = 223 K. The large temperature-dependent increase of the imaginary part of the susceptibility χ2(T), together with a simultaneous decrease of the real part of the susceptibility χ1(T), take place at the phase transition. These anomalies have been ascribed mainly to the SO4 group of the crystal structure.

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