Impact of Lattice Vibrations on Diffusion in Solids

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (31 May 2021) | Viewed by 2327

Special Issue Editor


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Guest Editor
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
Interests: dynamics in solids and liquids; energy materials; confinement; hydration; neutron scattering; spectroscopy

Special Issue Information

Dear Colleagues,

Understanding diffusion in a solid is highly relevant to cutting-edge material science from ionic conductivity in novel battery materials to thin film technology. Diffusion is usually a thermally activated process and, therefore, it is naturally coupled to lattice vibrations through the attempt frequency. Moreover, vibrations also cause the energy landscape and the potential barriers to be time-dependent. In addition, phonon instability can drive phase transitions and thereby facilitate migration processes.

Material manipulations, such as doping and nano-structuring, including surface treatment, are common tools of material design with a practically infinite number of possibilities. Therefore, computational screening and machine learning are extremely useful methods for both looking for new classes of materials with the desired properties and optimizing them. Experimental techniques, on the other hand, are needed to validate those predictions and verify the assumptions. However, rapid progress relies on our understanding of structure/dynamics and property relations.

With this Special Issue, we aim to provide an interdisciplinary collection of studies on the impact of lattice vibrations on diffusion in solids (ranging from highly important to negligible), which may pave the way to future applications. We would like to bring the ideas and tools of physicists closer to the practical world of material scientists. Therefore, we invite the submission of original research articles and high-quality reviews that describe complex topics and phenomena in a way that non-specialists can understand.

Dr. Fanni Jurányi
Guest Editor

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Keywords

  • Phonons, lattice dynamics, vibrations, softening
  • Anharmonicity and polarons
  • Energy barriers, Arrhenius’ law, and entropy
  • Diffusion, ionic conductivity, migration, jumps, and rotation
  • Collective and correlated motions
  • Mean square displacement and velocity auto-correlation
  • Vacancy, defects, interstitial, and surface reconstruction
  • Dimensionality, symmetry, distortion, orientation

Published Papers (1 paper)

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Research

15 pages, 2590 KiB  
Article
Low Frequency Vibrations and Diffusion in Disordered Polymers Bearing an Intrinsic Microporosity as Revealed by Neutron Scattering
by Reiner Zorn, Paulina Szymoniak, Mohamed A. Kolmangadi, Richard Malpass-Evans, Neil B. McKeown, Madhusudan Tyagi, Martin Böhning and Andreas Schönhals
Crystals 2021, 11(12), 1482; https://doi.org/10.3390/cryst11121482 - 29 Nov 2021
Cited by 2 | Viewed by 1711
Abstract
The microscopic diffusion and the low frequency density of states (VDOS) of PIM-EA-TB(CH3) are investigated by inelastic and quasi-elastic neutron scattering where also the demethylated counterpart of PIM-EA-TB(H2) is considered. These intrinsic microporous polymers are characterized by large BET [...] Read more.
The microscopic diffusion and the low frequency density of states (VDOS) of PIM-EA-TB(CH3) are investigated by inelastic and quasi-elastic neutron scattering where also the demethylated counterpart of PIM-EA-TB(H2) is considered. These intrinsic microporous polymers are characterized by large BET surface area values of several hundred m2/g and pore sizes between 0.5 and 2 nm. Detailed comparison is made to the archetype of polymers of intrinsic microporosity, PIM-1, and polynorbornenes also bearing a microporosity. Due to the wavelength of neutrons, the diffusion and vibrations can be addressed on microscopic length and time scales. From the inelastic neutron scattering experiments the low frequency density of states (VDOS) is estimated which shows excess contributions to the Debye-type VDOS known as Boson peak. It was found that the maximum frequency of the Boson peak decreases with increasing microporosity characterized by the BET surface area. However, besides the BET surface area, additional factors such as the backbone stiffness govern the maximum frequency of the Boson peak. Further the mean squared displacement related to microscopic motions was estimated from elastic fixed window scans. At temperatures above 175 K, the mean squared displacement PIM-EA-TB(CH3) is higher than that for the demethylated counterpart PIM-EA-TB(H2). The additional contribution found for PIM-EA-TB(CH3) is ascribed to the rotation of the methyl group in this polymer because the only difference between the two structures is that PIM-EA-TB(CH3) has methyl groups where PIM-EA-TB(H2) has none. A detailed comparison of the molecular dynamics is also made to that of PIM-1 and the microporous polynorbornene PTCNSi1. The manuscript focuses on the importance of vibrations and the localized molecular mobility characterized by the microscopic diffusion on the gas transport in polymeric separation membranes. In the frame of the random gate model localized fluctuations can open or close bottlenecks between pores to enable the diffusion of gas molecules. Full article
(This article belongs to the Special Issue Impact of Lattice Vibrations on Diffusion in Solids)
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