Electron and phonon band structures of palladium and palladium hydride: A review

IF 9.1 2区 化学 Q1 CHEMISTRY, INORGANIC & NUCLEAR Progress in Solid State Chemistry Pub Date : 2020-12-01 DOI:10.1016/j.progsolidstchem.2020.100285
S.S. Setayandeh, C.J. Webb, E. MacA. Gray
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引用次数: 14

Abstract

Palladium hydride was discovered more than 150 years ago and remains one of the most-studied interstitial metal hydrides because of the richness of its physical behaviours, which include ordered phases and anomalous properties at temperatures below 100 K, a superabundant-vacancy (SAV) phase with stoichiometry Pd3H4 formed at high temperature and pressure, and quenching of the enhanced Pauli paramagnetism of palladium. One of the most fascinating properties of palladium hydride is superconductivity at about 10 K without external pressure, in contrast to the newly-discovered polyhydride room-temperature superconductors that require megabar pressures. Moreover, the superconductivity exhibits an inverse isotope effect. Remarkably, modern first-principles approaches are unable to accurately predict the superconducting transition temperature by calculating the electron–phonon coupling constant within Migdal-Eliashberg theory. Anharmonicity of the hydrogen site potential is a key factor and poses a great challenge, since most theoretical approaches are based on the harmonic approximation. This review focuses on the electron and phonon band structures that underpin all such calculations, with palladium as a reference point. While the electron band structures of palladium and its monohydride are uncontroversial, the phonon band structure of palladium hydride in particular is problematic, with a realistic treatment of anharmonicity required – and largely yet to be achieved – to reproduce the results of inelastic neutron scattering experiments. In addition to the monohydride and SAV phases, possible higher hydrides are surveyed and the origin of the famous “50-K” anomaly in specific heat and other physical properties is critically reviewed.

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钯和氢化钯的电子和声子带结构综述
钯氢化物是在150多年前被发现的,由于其丰富的物理行为,包括在100 K以下的温度下有序相和异常性质,在高温高压下形成具有化学量Pd3H4的超丰空位(SAV)相,以及钯的增强泡利顺磁性的猝灭,因此它仍然是研究最多的间隙金属氢化物之一。氢化钯最令人着迷的特性之一是在没有外部压力的情况下,在大约10 K下具有超导性,这与新发现的需要兆巴压力的多氢化物室温超导体形成了鲜明对比。此外,超导性表现出逆同位素效应。值得注意的是,现代第一性原理方法无法通过计算Migdal-Eliashberg理论中的电子-声子耦合常数来准确预测超导转变温度。氢位势的非调和性是一个关键因素,也是一个巨大的挑战,因为大多数理论方法都是基于调和近似的。这篇综述的重点是电子和声子带结构,支持所有这些计算,以钯为参考点。虽然钯及其一氢化物的电子带结构是没有争议的,但氢化钯的声子带结构尤其存在问题,需要对非调和性进行现实的处理-而且很大程度上尚未实现-以再现非弹性中子散射实验的结果。除了一氢化物和SAV相外,还调查了可能的更高的氢化物,并对著名的“50-K”比热异常的起源和其他物理性质进行了严格的审查。
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来源期刊
Progress in Solid State Chemistry
Progress in Solid State Chemistry 化学-无机化学与核化学
CiteScore
14.10
自引率
3.30%
发文量
12
期刊介绍: Progress in Solid State Chemistry offers critical reviews and specialized articles written by leading experts in the field, providing a comprehensive view of solid-state chemistry. It addresses the challenge of dispersed literature by offering up-to-date assessments of research progress and recent developments. Emphasis is placed on the relationship between physical properties and structural chemistry, particularly imperfections like vacancies and dislocations. The reviews published in Progress in Solid State Chemistry emphasize critical evaluation of the field, along with indications of current problems and future directions. Papers are not intended to be bibliographic in nature but rather to inform a broad range of readers in an inherently multidisciplinary field by providing expert treatises oriented both towards specialists in different areas of the solid state and towards nonspecialists. The authorship is international, and the subject matter will be of interest to chemists, materials scientists, physicists, metallurgists, crystallographers, ceramists, and engineers interested in the solid state.
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