scholarly journals Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Wei Wang ◽  
Lijun Wu ◽  
Junjie Li ◽  
Niraj Aryal ◽  
Xilian Jin ◽  
...  
Keyword(s):  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Transient State ◽  
Single Crystal Sample ◽  
Domain Formation ◽  
Thermoelectric Devices ◽  
Crystal Sample ◽  
Anisotropic Thermal Conductivity ◽  
Anharmonic Lattice ◽  
Lattice Distortions

AbstractIdentifying and understanding the mechanisms behind strong phonon–phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c-axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices.

scholarly journals Matryoshka phonon twinning in α-GaN

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Bin Wei ◽  
Qingan Cai ◽  
Qiyang Sun ◽  
Yaokun Su ◽  
Ayman H. Said ◽  
...  
Keyword(s):  
Thermal Transport ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Electronic Devices ◽  
First Principles Calculations ◽  
Power Semiconductors ◽  
Anisotropic Thermal Conductivity ◽  
Phonon Dynamics ◽  
Generation Power

AbstractUnderstanding lattice dynamics is crucial for effective thermal management in electronic devices because phonons dominate thermal transport in most semiconductors. α-GaN has become a focus of interest as one of the most important third-generation power semiconductors, however, the knowledge on its phonon dynamics remains limited. Here we show a Matryoshka phonon dispersion of α-GaN with the complementary inelastic X-ray and neutron scattering techniques and the first-principles calculations. Such Matryoshka twinning throughout the basal plane of the reciprocal space is demonstrated to amplify the anharmonicity of the related phonons through creating abundant three-phonon scattering channels and cutting the lifetime of affected modes by more than 50%. Such phonon topology contributes to reducing the in-plane thermal transport, thus the anisotropic thermal conductivity of α-GaN. The results not only have implications for engineering the thermal performance of α-GaN, but also offer valuable insights on the role of anomalous phonon topology in thermal transport of other technically semiconductors.

GROWTH OF UNCRACKED BARIUM-SODIUM NIOBATE CRYSTALS

1990 ◽  
Vol 04 (16) ◽  
pp. 1017-1021 ◽  
Author(s):  
MASAYUKI TSUKIOKA ◽  
SHINICHIRO KUROIWA ◽  
YASUO TANOKURA ◽  
MICHIKO KOBAYASHI ◽  
MASAZI SHIMAZU ◽  
...  
Keyword(s):  
Single Crystal ◽  
Ferroelectric Phase Transition ◽  
Grown Crystal ◽  
Ferroelectric Phase ◽  
Experimental Result ◽  
Single Crystal Sample ◽  
Sodium Niobate ◽  
Crystal Sample ◽  
Lattice Distortions ◽  
Crystal Growth Condition

It is known that cracking occurs in Barium-Sodium Niobate, Ba 4 Na 2 Nb 10O30 (BNN), during Czochralski (cz) growth. This is due mainly to lattice distortions associated with the ferroelectric phase transition. We have studied the cz crystal growth condition for BNN without cracking, and found that high quality single crystals of BNN without cracking can be grown by using Gd-doped starting melt, i.e., Ba 4 Na 2 Nb 10O30-Ba3NaGdNb10O30 solid solution. In order to confirm the effect of Gd doping on the crystalline quality, Gd concentrations were measured by ICP for both the cz single crystal sample and the starting powder material. Gadlinium concentration in the as-grown crystal was about 0.195 mol %, nearly the same as that (2.0 mol %) in the starting material. Dielectric constant along c-axis, ε33, was measured at temperatures from 300 K to 870 K. The experimental result revealed that ε33 of the single crystal is about two times larger than that of BNN single crystal without Gd impurity in the temperature range from 300 K to 650 K.

scholarly journals Stability and equation of state of face-centered cubic and hexagonal close packed phases of argon under pressure

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Agnès Dewaele ◽  
Angelika D. Rosa ◽  
Nicolas Guignot ◽  
Denis Andrault ◽  
João Elias F. S. Rodrigues ◽  
...  
Keyword(s):  
Equation Of State ◽  
Single Crystal ◽  
Single Crystal Sample ◽  
Moderate Pressure ◽  
Face Centered Cubic ◽  
Experimental Conditions ◽  
Crystal Sample ◽  
Hexagonal Close Packed ◽  
Face Centered ◽  
Fcc Phase

AbstractThe compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: $$V_0$$ V 0 = 38.0 Å$$^3$$ 3 /at, $$K_0$$ K 0 = 2.65 GPa, $$K'_0$$ K 0 ′ = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure ($$\le$$ ≤ 20 GPa).

Extending the temperature sensing range using Eu3+ luminescence up to 865 K in a single crystal of EuPO4

2019 ◽  
Vol 21 (29) ◽  
pp. 16329-16336 ◽  
Author(s):  
Suchinder K. Sharma ◽  
Thomas Köhler ◽  
Jan Beyer ◽  
Margret Fuchs ◽  
Richard Gloaguen ◽  
...  
Keyword(s):  
Single Crystal ◽  
Temperature Sensing ◽  
Single Crystal Sample ◽  
Coupling Scheme ◽  
Excitation Wavelength ◽  
Crystal Sample ◽  
Sensing Range

Extending the temperature sensing range up to 865 K using an appropriate choice of excitation wavelength and coupling scheme in a single crystal sample of EuPO4.

scholarly journals Highly Anisotropic Thermal Transport in LiCoO2

2019 ◽  
Author(s):  
Hui Yang ◽  
Jia-Yue Yang ◽  
Christopher Savory ◽  
Jonathan Skelton ◽  
Benjamin Morgan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Lithium Ion Batteries ◽  
Phonon Dispersion ◽  
Lithium Ion ◽  
Boltzmann Transport ◽  
Heat Management ◽  
Positive Electrodes ◽  
Anharmonic Lattice ◽  
Anharmonic Interactions ◽  
The Impact

<div>LiCoO<sub>2</sub> is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li<sup>+</sup> and CoO<sub>2</sub><sup>-</sup> layers along the hexagonal <0001> axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO<sub>2</sub> using anharmonic lattice dynamics based on quantum chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ≈ 6 times higher than that along the c axis based on the phonon Boltzmann transport. The low thermal conductivity (< 10Wm<sup>-1</sup>K<sup>-1</sup>) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO<sub>2</sub><sup>-</sup> networks, as well as grain boundary scattering. The impact on heat management and thermal processes in lithium ion batteries based on layered positive electrodes is discussed.</div>

A Modified Thermal Boundary Resistance Model for FCC Structures

2009 ◽  
Author(s):  
Ruijie Zhao ◽  
Yunfei Chen ◽  
Kedong Bi ◽  
Meihui Lin ◽  
Zan Wang
Keyword(s):  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Theoretical Calculations ◽  
Theoretical Models ◽  
Md Simulations ◽  
Boundary Resistance ◽  
Nonequilibrium Molecular Dynamics ◽  
Thermal Boundary Resistance ◽  
Inelastic Channel ◽  
The Right

A modified lattice-dynamical model is proposed to calculate the thermal boundary resistance at the interface between two fcc lattices. The nonequilibrium molecular dynamics (MD) simulation is employed to verify the theoretical calculations. In our physical model, solid crystal argon is set at the left side and the right side structure properties are tunable by setting the atomic mass and the interactive energy strength among atoms with different values. In the case of mass mismatch, the predictions of the lattice-dynamical (LD) model agree well at low temperature while the calculations of the diffuse mismatch model (DMM) based on the detailed phonon dispersion agree well at high temperature with the MD simulations. The modified LD model, considering a partially specular and partially diffuse phonon scattering, can explain the simulations reasonably in the whole temperature rage. The good agreement between the theoretical calculations and the simulations may be attributed to that phonon scattering mechanisms are dominated by elastic scattering at the perfect interfaces. In the case of interactive energy strength mismatch, the simulations are under the predictions of both the theoretical models, which may be attributed to the fact that this mismatch can bring about an outstanding contribution to opening up an inelastic channel for heat transfer at the interfaces.

Nuclear Scattering

2020 ◽  
pp. 127-184
Author(s):  
Andrew T. Boothroyd
Keyword(s):  
Cross Sections ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Spin Echo ◽  
Harmonic Approximation ◽  
Approximate Expression ◽  
Neutron Spin ◽  
Response Functions ◽  
Nuclear Scattering ◽  
Scattering Cross

This chapter contains an overview of the different types of structural dynamics found in condensed matter, and the associated neutron scattering cross-sections. The scattering dynamics of the harmonic oscillator is discussed, and an expression for the Debye-Waller factor is obtained. In the case of crystalline solids, the vibrational spectrum in the harmonic approximation is described, including the phonon dispersion and the cross-sections for one-phonon coherent and incoherent scattering. Multi-phonon scattering is discussed briefly. For non-crystalline matter, the time-dependent van Hove correlation and response functions are introduced, and their relation to the scattering cross-section established. An approximate expression for the correlation function is obtained from the classical form. Partial correlation and response functions are defined for multicomponent systems. The technique of neutron Compton scattering as a probe of single-particle recoil dynamics is described. Quasielastic and neutron spin-echo spectroscopy are introduced, as well as examples of relaxational dynamics which these techniques can measure.

scholarly journals Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Lina Yang ◽  
Austin J. Minnich
Keyword(s):  
Thermal Conductivity ◽  
Monte Carlo ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Computational Study ◽  
Phonon Transport ◽  
Nanocrystalline Si

Abstract Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.

A Comparison of Small Angle Neutron Scattering and X-Ray Diffraction Studies of Cobalt Precipitates in A Cu-0.95 at. % Co Alloy

1986 ◽  
Vol 82 ◽  
Author(s):  
S. Spooner ◽  
S. Iida ◽  
B. C. Larson
Keyword(s):  
Small Angle ◽  
Large Angle ◽  
Detailed Comparison ◽  
Scattering Data ◽  
Single Crystal Sample ◽  
X Ray Diffraction ◽  
Data Set ◽  
Crystal Sample ◽  
X Ray ◽  
Angle Scattering

ABSTRACTA detailed comparison of small-angle scattering (SANS) and large angle x-ray diffraction methods of characterization of precipitates was undertaken. Cobalt-rich precipitates on the order of 50 Å developed after a 17 hour anneal at 570°C were studied in a single crystal sample with SANS and with diffuse x-ray scattering near the (400)Bragg peak. Each scattering data set was analyzed independently in terms of a distribution of precipitate sizes; a detailed comparison is made of the size distribution obtained. A small interparticle interference effect is seen.

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