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Annealed bulk crystals of barium titanate (BaTiO3) exhibit persistent photoconductivity (PPC) at room temperature. Samples were annealed in a flowing gas of humid argon and hydrogen, with a higher flow rate corresponding to larger PPC. When exposed to sub-bandgap light, a broad infrared (IR) absorption peak appears at 5000 cm−1(2 μm), attributed to polaronic or free-carrier absorption from electrons in the conduction band. Along with the increased IR absorption, electrical resistance is reduced by a factor of approximately two. The threshold photon energy for PPC is 2.9 eV, similar to the case of SrTiO3. This similarity suggests that the mechanisms are similar: an electron in substitutional hydrogen (HO) is photoexcited into the conduction band, causing the proton to leave the oxygen vacancy and attach to a host oxygen atom. The barrier to recover to the ground state is large such that PPC persists at room temperature.
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Room temperature flash of single crystal titania: Electronic and optical properties
Abstract A single‐crystal specimen of rutile (titania) was flashed repetitively, while increasing the electric field after each cycle. As expected, the flash onset temperature continued to drop modestly at higher fields. However, when the field was increased from 400 to 450 V cm–1, the flashed onset fell dramatically down to room temperature. We have investigated the electrical and optical properties of this room temperature flashed specimen (called SZ). The specimen was electronically conducting. Optical absorption spectroscopy revealed a narrow band of new energy levels that were generated just below the conduction band. The gap between the conduction band and this flash‐induced energy level agreed with the peak in the electroluminescence spectrum. Optical second harmonic generation (SHG) is reported. The flash‐on condition significantly lowered the SHG, which rebounded when the flash was turned off. This result suggests that the structure becomes more centrosymmetric in the state of flash, which may represent a disordered state of defects. The possibility of studying flash behavior at room temperature, without a furnace (as in SZ type specimens), opens a considerable simplification for in‐situ characterization of flash behavior. For example, a possible relationship between memristor physics and the flash phenomenon can be studied.
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- Award ID(s):
- 2011839
- PAR ID:
- 10372708
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 106
- Issue:
- 1
- ISSN:
- 0002-7820
- Format(s):
- Medium: X Size: p. 46-52
- Size(s):
- p. 46-52
- Sponsoring Org:
- National Science Foundation
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