Structural, electrical, and optical properties of La1-zYzHx switchable mirrors

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Gogh, A.T.M. van and Nagengast, D.G. and Kooij, E.S. and Koeman, N.J. and Rector, J.H. and Griessen, R. and Flipse, C.F.J. and Smeets, R.J.J.G.A.M. (2001) Structural, electrical, and optical properties of La1-zYzHx switchable mirrors. Physical Review B: Condensed matter and materials physics, 63 (19). p. 195105. ISSN 1098-0121

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Abstract:Thin La1-zYzHx films, in the composition range 0<z<1 and 0<x<3, are studied using x-ray diffraction, dc resistivity measurements, reflectance-transmittance measurements, and ellipsometry in the visible and near-infrared spectral range. For x=0 the structural phase diagram is similar to that of the bulk system. Upon hydrogen absorption and desorption, the La1-zYzHx films do not disproportionate. All dihydrides have a fcc structure with a continuous shift of the lattice parameter, whereas the trihydrides undergo a transition from a fcc lattice structure for 0<z<0.67 to a hexagonal lattice structure for 0.81<z<1. No significant thin-film effects occur in the structural, electrical, and optical properties, whereas disorder effects are observed in the x-ray coherence length, the electron relaxation time at both zero and optical frequencies, and in the optical properties of the trihydrides. In LaH2 a similar dihydride transmission window is observed as in YH2. The suppression of this window upon alloying is a disorder effect. As in the case of their parent materials, all La1-zYzHx alloys (both cubic and hexagonal) exhibit a metal-insulator transition for 2<x<3, which is a clear demonstration of the robustness of the metal-insulator transition in switchable mirrors. The optical band-gap shifts from 1.87±0.03 eV for LaH3 to 2.63±0.03 eV for YH3. The optical properties suggest that the fundamental band gap is 1–1.8 eV lower.

Item Type:Article
Copyright:© 2001 The American Physical Society
Link to this item:http://purl.utwente.nl/publications/75187
Official URL:http://dx.doi.org/10.1103/PhysRevB.63.195105
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Metis ID: 202316