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Title: Phonon thermal transport through tilt grain boundaries in strontium titanate

Abstract

In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO{sub 3}. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO{sub 3} contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have themore » same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.« less

Authors:
; ; ; ;  [1]; ;  [2]
  1. Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611 (United States)
  2. Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)
Publication Date:
OSTI Identifier:
22314299
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 7; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 36 MATERIALS SCIENCE; COMPARATIVE EVALUATIONS; GRAIN BOUNDARIES; MODE CONVERSION; MOLECULAR DYNAMICS METHOD; MONOCRYSTALS; PHONONS; REFLECTION; SCATTERING; SIMULATION; STRONTIUM; STRONTIUM TITANATES; TEMPERATURE DEPENDENCE; WAVE PACKETS

Citation Formats

Zheng, Zexi, Chen, Xiang, Yang, Shengfeng, Xiong, Liming, Chen, Youping, Deng, Bowen, and Chernatynskiy, Aleksandr. Phonon thermal transport through tilt grain boundaries in strontium titanate. United States: N. p., 2014. Web. doi:10.1063/1.4893648.
Zheng, Zexi, Chen, Xiang, Yang, Shengfeng, Xiong, Liming, Chen, Youping, Deng, Bowen, & Chernatynskiy, Aleksandr. Phonon thermal transport through tilt grain boundaries in strontium titanate. United States. doi:10.1063/1.4893648.
Zheng, Zexi, Chen, Xiang, Yang, Shengfeng, Xiong, Liming, Chen, Youping, Deng, Bowen, and Chernatynskiy, Aleksandr. Thu . "Phonon thermal transport through tilt grain boundaries in strontium titanate". United States. doi:10.1063/1.4893648.
@article{osti_22314299,
title = {Phonon thermal transport through tilt grain boundaries in strontium titanate},
author = {Zheng, Zexi and Chen, Xiang and Yang, Shengfeng and Xiong, Liming and Chen, Youping and Deng, Bowen and Chernatynskiy, Aleksandr},
abstractNote = {In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO{sub 3}. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO{sub 3} contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.},
doi = {10.1063/1.4893648},
journal = {Journal of Applied Physics},
number = 7,
volume = 116,
place = {United States},
year = {Thu Aug 21 00:00:00 EDT 2014},
month = {Thu Aug 21 00:00:00 EDT 2014}
}
  • Abstract not provided.
  • In this paper, we investigate the role of grain boundaries in polycrystalline (Ba{sub x}Sr{sub 1-x})Ti{sub 1+y}O{sub 3+z} films, grown by metal organic vapor deposition, in the accommodation of nonstoichiometry, as well as their role in the strong composition dependence of the electric and dielectric behavior observed in these films. High-spatial resolution electron energy-loss spectroscopy is used for the analysis of composition and structural changes at grain boundaries, as a function of film composition. The existence of amorphous, titanium rich, TiO{sub 2}-like phases at the grain boundaries of films with large amounts of excess Ti (y {>=} 0.08) may explain themore » non-monotonic resistance degradation behavior of the films as a function of Ti content. However, we show that a grain boundary phase model fails to explain the strong composition dependence of the dielectric behavior. Electron energy-loss spectra indicate a distortion of the Ti-O octahedra in the grain interiors in samples with increasing Ti excess. The decrease of the dielectric constant with increasing amounts of excess Ti is therefore more likely due to Ti accommodation in the grain interiors.« less
  • This study focuses on the proper characterization of temperature profiles across grain boundaries (GBs) in order to calculate the correct interfacial thermal resistance (ITR) and reveal the influence of GB geometries onto thermal transport. The solid-solid interfaces resulting from the orientation difference between the (001), (011), and (111) copper surfaces were investigated. Temperature discontinuities were observed at the boundary of grains due to the phonon mismatch, phonon backscattering, and atomic forces between dissimilar structures at the GBs. We observed that the temperature decreases gradually in the GB area rather than a sharp drop at the interface. As a result, threemore » distinct temperature gradients developed at the GB which were different than the one observed in the bulk solid. This behavior extends a couple molecular diameters into both sides of the interface where we defined a thickness at GB based on the measured temperature profiles for characterization. Results showed dependence on the selection of the bin size used to average the temperature data from the molecular dynamics system. The bin size on the order of the crystal layer spacing was found to present an accurate temperature profile through the GB. We further calculated the GB thickness of various cases by using potential energy (PE) distributions which showed agreement with direct measurements from the temperature profile and validated the proper binning. The variation of grain crystal orientation developed different molecular densities which were characterized by the average atomic surface density (ASD) definition. Our results revealed that the ASD is the primary factor affecting the structural disorders and heat transfer at the solid-solid interfaces. Using a system in which the planes are highly close-packed can enhance the probability of interactions and the degree of overlap between vibrational density of states (VDOS) of atoms forming at interfaces, leading to a reduced ITR. Thus, an accurate understanding of thermal characteristics at the GB can be formulated by selecting a proper bin size.« less
  • The zero-field electrical transport properties of 24{degree} [001] tilt bicrystal grain boundaries in YBa{sub 2}Cu{sub 3}O{sub 7} were found to be in excellent agreement with the Ambegaokar{endash}Halperin model over an extended range of currents and voltages. This model gives a firm basis for characterizing and comparing boundaries, and provides two independent measures of the critical current, which were proportional to (1{minus}{ital T}/{ital T}{sub {ital c}}){sup 2} close to the transition temperature {ital T}{sub {ital c}}. {copyright} {ital 1996 American Institute of Physics.}