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Effect of sintering temperature and heat treatment on electrical properties of indium oxide based ceramics
Indium oxide based ceramics with bismuth oxide addition were sintered in air in the temperature range 800-1300 ÂșC. Current-voltage characteristics of In2O3-Bi2O3 ceramics sintered at different temperatures are weakly nonlinear. After an additional heat treatment in air at about 200 ÂșC samples sintered at a temperature within the narrow range of about 1050-1100 ÂșC exhibit a current-limiting effect accompanied by low-frequency current oscillations. It is shown that the observed electrical properties are controlled by the grain-boundary barriers and the heat treatment in air at 200 ÂșC leads to the decrease in the barrier height. Electrical measurements, scanning electron microscopy and X-ray photoelectron spectroscopy results suggest that the current-limiting effect observed in In2O3-Bi2O3 can be explained in terms of the modified barrier model proposed earlier for the explanation of similar effect in In2O3-SrO ceramics
Current limiting and negative differential resistance in indium oxide based ceramics
Indium oxide based ceramics with bismuth oxide addition were sintered in air in the temperature range 800-1300 ÂșC. Current-voltage characteristics of In2O3-Bi2O3 ceramics sintered at different temperatures are weakly nonlinear. After an additional heat treatment in air at about 200 ÂșC samples sintered at a temperature within the narrow range of about 1050-1100 ÂșC exhibit a current-limiting effect accompanied by low-frequency current oscillations. It is shown that the observed electrical properties are controlled by the grain-boundary barriers and the heat treatment in air at 200 ÂșC leads to the decrease in the barrier height. Electrical measurements, scanning electron microscopy and X-ray photoelectron spectroscopy results suggest that the current-limiting effect observed in In2O3-Bi2O3 may be explained in terms of a modified barrier model; the observed current-limiting effect is the result of an increase of barrier height with increasing electric field, due to additional oxygen absorption. It is found that In2O3-Bi2O3-Co3O4-Cr2O3 ceramic exhibits current-voltage characteristics with negative differential resistance due to Joule micro heating.This study was performed in part in the frames of the project SEP-2003-C02-42821, CONACYT, MĂ©xico. Funding from the Royal Society, United Kingdom (2007R1/R26999) is gratefully acknowledged
Photovoltaic effect in multi-domain ferroelectric perovskite oxides
We propose a device model that elucidates the role of domain walls in the
photovoltaic effect in multi-domain ferroelectric perovskites. The model
accounts for the intricate interplay between ferroelectric polarization, space
charges, photo-generation and electronic transport. When applied to bismuth
ferrite, results show a significant electric potential step across both
71-degree and 109-degree domain walls, which in turn contributes to the
photovoltaic (PV) effect. We also find a strong correlation between
polarization and oxygen octahedra tilts, which indicates the nontrivial role of
the latter in the PV effect. The domain wall-based PV effect is further shown
to be additive in nature, allowing for the possibility of generating
above-bandgap voltag
Experimental Study of the Intrinsic and Extrinsic Transport Properties of Graphite and Multigraphene Samples
This work deals with the intrinsic and extrinsic properties of the graphene
layers inside the graphite structure, in particular the influence of defects
and interfaces. We discuss the evidence for ballistic transport found in
mesoscopic graphite samples and the possibility to obtain the intrinsic carrier
density of graphite, without the need of free parameters or arbitrary
assumptions. The influence of internal interfaces on the transport properties
of bulk graphite is described in detail. We show that in specially prepared
multigraphene samples the transport properties show clear signs for the
existence of granular superconductivity within the graphite interfaces. We
argue that the superconducting-insulator or metal-insulator transition (MIT)
reported in the literature for bulk graphite is not intrinsic of the graphite
structure but it is due to the influence of these interfaces. Current-Voltage
characteristics curves reveal Josephson-like behavior at the interfaces with
superconducting critical temperatures above 150K.Comment: 26 pages, 15 figures. To be published in "Graphene, Book 2" by
Intech, Open Access Publisher 2011, ISBN: 979-953-307-180-
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