Electronic structure of metal hydrides. II. Band theory of Sc<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and Y<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mm

Peterman, D. J.; Harmon, B. N.; Marchiando, Jay Francis; Weaver, J. H.

doi:10.1103/physrevb.19.4867

Cited by 109 publications

(24 citation statements)

References 28 publications

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“…This phase is quite well characterized from measurements on bulk samples and is metallic with a conductivity which is about a factor of 5 higher than that of yttrium metal. There have been detailed experimental studies of the optical properties [2] which could be interpreted in terms of conventional, selfconsistently calculated one-electron band structures [3]. For x .…”

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Theoretical Prediction of the Structure of InsulatingYH3

1997

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Density functional calculations of the total energy have been used to determine minimum energy structures for YH 3 . Small, symmetry lowering displacements of the hydrogen atoms lead to a structure with an energy which is lower than that of any other structure considered so far and the opening of a large band gap sufficient to explain the recently observed metal-insulator transition in the YH x system. [ S0031-9007(97) There has recently been a breakthrough in the preparation and study of the physical properties of rare-earth hydrides [1]. By depositing thin films (ϳ500 nm) of rare-earth metals on a transparent substrate and coating them with an optically thin protective layer of palladium through which hydrogen could diffuse, it was possible to observe a metal-insulator transition as a function of the H concentration optically as well as in electrical transport measurements. The transition could be cycled repeatedly without any apparent deterioration of the sample.For 2 , x , 3 Huiberts et al.[1] interpreted their extensive optical and electrical measurements on YH x in terms of a cubic dihydride b phase and of a hexagonal trihydride g phase. In the cubic YH 2 phase the two tetrahedral sites in the fcc Y lattice are (nominally) occupied and the octahedral sites unoccupied. This phase is quite well characterized from measurements on bulk samples and is metallic with a conductivity which is about a factor of 5 higher than that of yttrium metal. There have been detailed experimental studies of the optical properties [2] which could be interpreted in terms of conventional, selfconsistently calculated one-electron band structures [3]. For x . 2 the octahedral sites are believed to become randomly occupied until the trihydride phase is nucleated when x exceeds 2.09 [4]. The properties of the hexagonal YH 3 phase were not well known until now because bulk samples disintegrate when x approaches three. To explain their measurements, Huiberts et al. required the hexagonal YH 3 phase to have a band gap of 1.8 eV and, for substoichiometric trihydrides YH 32d , shallow donor states were assumed to be formed about 0.4 eV below the conduction band edge. This picture was supported by Hall measurements, a negative temperature coefficient of the electrical resistivity ͑dr͞dT͒, and the dependence of the resistivity on d [1,5]. The metal-insulator transition in YH x occurs on going from the cubic b phase to the hexagonal g phase.A number of electronic structure calculations have been performed for YH 3 . In the most recent work [6,7] based on the HoD 3 structure derived from neutron scattering experiments [8][9][10], it was concluded that YH 3 should be metallic which is in disagreement with Huiberts' interpretation of his experiments. To reconcile these contradictory results, strong correlation effects have been invoked [1,7,11]. In this Letter we use Car-Parrinello calculations to determine minimum energy structures for hexagonal YH 3 [12]. We show that although YH 3 is metallic in the high symmetry HoD 3 structure, there exists...

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“…A number of electronic structure calculations have been performed for YH 3 . In the most recent work [6,7] based on the HoD 3 structure derived from neutron scattering experiments [8][9][10], it was concluded that YH 3 should be metallic which is in disagreement with Huiberts' interpretation of his experiments.…”

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Theoretical Prediction of the Structure of InsulatingYH3

1997

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“…The (screened) plasma energy of YH 2 is 1.64 eV [30], explaining the sharp decrease of the reflectance around this energy. The reflectance at higher energies is caused by interband absorptions from the conduction band into higher d-derived bands as was shown by Peterman et al [31]. As a result, there is neither a strong reflectance nor a strong absorption at intermediate photon energies, giving rise to the transmittance window in Fig.…”

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Isotope Effects in Switchable Metal-Hydride Mirrors

1999

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Measurements of optical reflectance, transmittance, and electrical resistivity on the switchable mirror systems YH x and YD x show that the absorption of hydrogen induces the same variations as that of deuterium. In both cases there is a weak transparency window for the metallic dihydride (dideuteride) phase and a yellowish transparency in the insulating trihydride (trideuteride) phase. The slightly higher electrical resistivity of the deuterides is related to the lower energy of their optical phonons. The absence of significant isotope effects in the optical properties of YH x ͑ YD x ͒ is at variance with Peierlslike theoretical models. It is, however, compatible with strong electron correlation models. PACS numbers: 71.30. + h, Spectacular changes in the optical and electrical properties were recently discovered [1,2] in metal-hydride films of yttrium and lanthanum near their metal-insulator transition: the dihydrides are excellent metals and shiny while the trihydrides are insulators and transparent in the visible part of the optical spectrum. The metal-insulator (MI) transition from a shiny to a transparent state is reversible and simply induced at room temperature by changing the surrounding hydrogen gas pressure or electrolytic cell potential [3-5]. All trivalent rare-earth hydrides and even some of their alloys exhibit switchable optical and electrical properties [4,6]. In the transparent state they have characteristic colors: for example, YH 3 is yellowish, LaH 3 red, while some alloys are colorless. These films can therefore be used as switchable mirrors.Soon after their discovery it was realized that the insulating state of the switchable mirrors could probably not be understood in terms of existing one-electron theories, since Wang and Chou [7,8] and Dekker et al. [9] had concluded a few years earlier from self-consistent band structure calculations, that YH 3 was a semimetal with, in fact, a very large band overlap (1.5 eV). By minimizing the total energy, these authors found that the HoD 3 -(P3c1)-type structure was energetically more favorable than the cubic BiF 3 -type structure originally assumed by Switendick [10]. By allowing for Peierls-like displacements of the hydrogen atoms near the metal planes, Wang and Chou [8] found that the total energy could be further lowered by an extra 30 meV per YH 3 . They finally obtained an electronic band structure with only one electron band and one hole band crossing the Fermi energy E F near the center of the Brillouin zone. These difficulties stimulated theorists to reconsider the YH x and LaH x systems. Somewhat similarly to the situation for high-T c superconductors, two clearly different lines of thought have been proposed so far: Peierls-like band structure models and strongly correlated electron models.(i) Strong electron correlation: Already in 1995 Sawatzky [12] suggested that electron correlation effects might explain the existence of the large optical gap in YH 3 . Along the same lines Ng et al. [13,14] discuss the MI transition in LaH x starting ...

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“…The first, suggested and actually begun by D. L. Johnson, was for YH 2 with the zincblende, rather than the CaF 2 , fluorite structure (67). With this structure, all octahedral, but only half of the tetrahedral, sites are filled, giving the octahedral hydrogen atom 4 nearest-neighbor hydrogen atoms.…”

Section: Energy Bands Of Caf 2 -Structured Sch 2 and Yhmentioning

confidence: 99%

Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

Peterman

1980

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Electronic structure of metal hydrides. II. Band theory of ScH2and YH2

Cited by 109 publications

References 28 publications

Theoretical Prediction of the Structure of InsulatingYH3

Theoretical Prediction of the Structure of InsulatingYH3

Isotope Effects in Switchable Metal-Hydride Mirrors

Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

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