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Barium titanate breaks Ohm's law

Posted: 28 Sep 2010 ?? ?Print Version ?Bookmark and Share

Keywords:barium titanate? ceramics? resistance?

Some barium titanate (BT) ceramics do not follow Ohm's Law, researchers report in the journal Applied Physics Letters.

Several slightly doped high-purity barium titanate (BT) ceramics being investigated by the group showed gradually changing electrical resistance upon applying or removing a voltage. The effect was seen consistently regardless of the temperature or whether the experiments were conducted in vacuum, air, or in an oxygen atmosphere. The time to stabilize and the final, steady-state resistance were, however, both temperature-dependent. This may help explain how ceramics used in electrical circuits degrade.

"I was not immediately convinced myself about the non-Ohm's Law behavior," said Anthony West, professor of electroceramics and solid state chemistry at the University of Sheffield, England. "Interfacial effects are well known for their non-Ohmic behavior. We needed to be really convinced that our results were not influenced in some way by interfacial effects."

West proposes the that mechanism for the non-Ohm behavior is the ionization of only one of the two extra electrons from oxygen atoms that are attached to dopant atoms. This process leaves behind a positively charged "hole" that can move fairly readily in what is called a hole current.

Similar results with zinc and magnesium dopants were published earlier this year in other technical journals. Calcium, zinc and magnesium are known as "acceptor" dopants, which can promote hole currents.

Undoped BT and "donor"-doped materials did not exhibit this unusual behavior. West believes that these results may ultimately lead to a better understanding of how ceramics used in electrical circuits degrade and may possibly even stimulate new insights into high-temperature superconductivity mechanisms in oxide ceramics.

The article, "Field enhanced bulk conductivity of acceptor-doped BaTi1-xCaxO3-x ceramics" by Nahum Maso, Marta Prades, Hector Beltran, Eloisa Cordoncillo, Derek C. Sinclair, and Anthony R. West appears in the journal Applied Physics Letters.

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