The direct optical bandgap in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me = Fe or Mn) ceramics fabricated by the solid state reaction method varies from 3.2 eV for KNbO3 down to 2.2 eV for 0.95KNbO3-0.05BiYbO3, as revealed by optical spectroscopic ellipsometry. This narrowing of bandgap is accompanied by an apparent increase of the room-temperature relative permittivity from 320 for KNbO3 to 900 for 0.95KNbO3-0.05BiYbO3. All compositions studied exhibit dielectric anomalies associated with structural phase transitions, and their ferroelectric nature is corroborated by the presence of a sharp mixed mode (at ∼190 cm−1) and by a Fano-type resonant dip in their Raman spectra.
Band gap narrowing in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me=Fe or Mn) ceramics
Cristina Pascual-Gonzalez, Giorgio Schileo, Antonio Feteira; Band gap narrowing in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me=Fe or Mn) ceramics. Appl. Phys. Lett. 26 September 2016; 109 (13): 132902. https://doi.org/10.1063/1.4963699
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