Details
| Original language | English |
|---|---|
| Pages (from-to) | 158-166 |
| Number of pages | 9 |
| Journal | Physica C: Superconductivity and its Applications |
| Volume | 166 |
| Issue number | 1-2 |
| Publication status | Published - 1 Mar 1990 |
Abstract
The normal reflectivity of Ti4O7 (T = 290 K) is measured in the range of 0.1 to 3 eV. The reflectivity shows a minimum which corresponds to the collective resonance of all Ti3+ valences. The optical absorption as calculated from the diffuse reflectivity of Ti4O7 is investigated in the spectral range of 0.5 to 2.5 eV and at temperatures between 10 and 300 K. A broad asymmetrical absorption band with a maximum at about 0.7 eV and an absorption sideband at about 1.5 eV is observed. The overall line shape is explained by the polaronic absorption mechanism. From room temperature down to the metal-insulator transition at T>m ≈ 150 K the total polaronic absorption cross section remains constant. It drops down in the intermediate phase (125-150 K) and then increases with decreasing temperature below the Verwey transition at Tv ≈ 125 K. The increasing absorption cross section below Tv as well as the shift of the peak position to lower energy is in accordance with the gap opening at ≈ 0.2 eV previously reported (Kaplan et al. [1]) and is explained by the separation of single polaronic from bipolaronic energy levels. The magnetic susceptibility of Ti4O7 is discussed with respect to an exchange pairing mechanism above and below Tm. It is suggested that a melting of the bipolaronic state during the metal-insulator transition results in a fluctuating valence bond system above Tm.
ASJC Scopus subject areas
- Materials Science(all)
- Electronic, Optical and Magnetic Materials
- Physics and Astronomy(all)
- Condensed Matter Physics
- Energy(all)
- Energy Engineering and Power Technology
- Engineering(all)
- Electrical and Electronic Engineering
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In: Physica C: Superconductivity and its Applications, Vol. 166, No. 1-2, 01.03.1990, p. 158-166.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Single polaron and bipolaron absorption in Ti4O7 above and below the metal-insulator transition
AU - Rüscher, C.
AU - Rüffer, N.
AU - Seiwert, F. J.
AU - Gruehn, R.
N1 - Funding Information: The magnetica nd conductivity measurementsw ere done using the facilities of the Arrhenius Laboratory of Stockholm University. We are thankful to Prof. Nygren and colleagues for their kind support. CR thanks Dr. H. Behrens and Dr. U. Bismayer for helpful discussions. CR and NR were supported in part by SFB 173 and BMFT 13N5738 7.
PY - 1990/3/1
Y1 - 1990/3/1
N2 - The normal reflectivity of Ti4O7 (T = 290 K) is measured in the range of 0.1 to 3 eV. The reflectivity shows a minimum which corresponds to the collective resonance of all Ti3+ valences. The optical absorption as calculated from the diffuse reflectivity of Ti4O7 is investigated in the spectral range of 0.5 to 2.5 eV and at temperatures between 10 and 300 K. A broad asymmetrical absorption band with a maximum at about 0.7 eV and an absorption sideband at about 1.5 eV is observed. The overall line shape is explained by the polaronic absorption mechanism. From room temperature down to the metal-insulator transition at T>m ≈ 150 K the total polaronic absorption cross section remains constant. It drops down in the intermediate phase (125-150 K) and then increases with decreasing temperature below the Verwey transition at Tv ≈ 125 K. The increasing absorption cross section below Tv as well as the shift of the peak position to lower energy is in accordance with the gap opening at ≈ 0.2 eV previously reported (Kaplan et al. [1]) and is explained by the separation of single polaronic from bipolaronic energy levels. The magnetic susceptibility of Ti4O7 is discussed with respect to an exchange pairing mechanism above and below Tm. It is suggested that a melting of the bipolaronic state during the metal-insulator transition results in a fluctuating valence bond system above Tm.
AB - The normal reflectivity of Ti4O7 (T = 290 K) is measured in the range of 0.1 to 3 eV. The reflectivity shows a minimum which corresponds to the collective resonance of all Ti3+ valences. The optical absorption as calculated from the diffuse reflectivity of Ti4O7 is investigated in the spectral range of 0.5 to 2.5 eV and at temperatures between 10 and 300 K. A broad asymmetrical absorption band with a maximum at about 0.7 eV and an absorption sideband at about 1.5 eV is observed. The overall line shape is explained by the polaronic absorption mechanism. From room temperature down to the metal-insulator transition at T>m ≈ 150 K the total polaronic absorption cross section remains constant. It drops down in the intermediate phase (125-150 K) and then increases with decreasing temperature below the Verwey transition at Tv ≈ 125 K. The increasing absorption cross section below Tv as well as the shift of the peak position to lower energy is in accordance with the gap opening at ≈ 0.2 eV previously reported (Kaplan et al. [1]) and is explained by the separation of single polaronic from bipolaronic energy levels. The magnetic susceptibility of Ti4O7 is discussed with respect to an exchange pairing mechanism above and below Tm. It is suggested that a melting of the bipolaronic state during the metal-insulator transition results in a fluctuating valence bond system above Tm.
UR - http://www.scopus.com/inward/record.url?scp=0025399170&partnerID=8YFLogxK
U2 - 10.1016/0921-4534(90)90568-Y
DO - 10.1016/0921-4534(90)90568-Y
M3 - Article
AN - SCOPUS:0025399170
VL - 166
SP - 158
EP - 166
JO - Physica C: Superconductivity and its Applications
JF - Physica C: Superconductivity and its Applications
SN - 0921-4534
IS - 1-2
ER -