Infrared optical properties of α-alumina with the approach to melting: γ-like tetrahedral structure and small polaron conduction

J. F. Brun and L. del Campo and D. De Sousa Meneses and P. Echegut

The normal spectral emittance of α-Al2O3 single crystal has been measured from room temperature up to the liquid state and from 20 cm⁻¹ up to 10000 cm⁻¹, in two polarization configurations. The spectra were fitted with a semi-quantum dielectric function model. AlO4 structure units are revealed within the phonon spectral range more than a hundred degrees below the melting point when heating from the solid state. In parallel, the anomalous increase of emittance observed within the transparency spectral range with the approach to melting appears strongly correlated. Implications on the electronic structure are discussed: the existence of small polaron conduction is suggested which has never been mentioned before.

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Materials
Curve 1
Temperature, K: 298 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 2
Temperature, K: 1023 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 3
Temperature, K: 1581 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 4
Temperature, K: 1865 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 5
Temperature, K: 2053 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 6
Temperature, K: 2190 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 7
Temperature, K: 2249 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 8
Temperature, K: 2269 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 9
Temperature, K: 2285 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 10
Temperature, K: 2300 Polarization: E ∥ c-axis (extraordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 11
Temperature, K: 298 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 12
Temperature, K: 863 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 13
Temperature, K: 1053 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 14
Temperature, K: 1217 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 15
Temperature, K: 1329 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 16
Temperature, K: 1452 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 17
Temperature, K: 1603 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 18
Temperature, K: 1886 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 19
Temperature, K: 2056 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 20
Temperature, K: 2154 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 21
Temperature, K: 2197 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 22
Temperature, K: 2248 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 23
Temperature, K: 2274 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 24
Temperature, K: 2285 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).
Curve 25
Temperature, K: 2303 Polarization: E ⊥ c-axis (ordinary ray) Composition (weight percent), Specifications and Remarks: 0.5-mm thick, optically polished high purity (>99.99%) α-Al2O3 single crystal plate; measured in open air with a unique CEMHTI emissometer; source wavenumber axis and point count reconstructed from the raw OPUS data block (see note on header metadata).