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Phys Rev Lett. 2010 Apr 9;104(14):147602. Epub 2010 Apr 9.

Persistence of ferroelectricity in BaTiO3 through the insulator-metal transition.

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National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.


The ferroelectric BaTiO(3) is a band-gap insulator. Itinerant electrons can be introduced in this material by doping, for example, with oxygen vacancies. Above a critical electron concentration of n(c) approximately 1 x 10(20) cm(-3), BaTiO(3-delta) becomes metallic. This immediately raises a question: Does metallic BaTiO(3-delta) still retain ferroelectricity? One may expect itinerant electrons to destroy ferroelectricity as they screen the long-range Coulomb interactions. We followed the phase transitions in BaTiO(3-delta) as a function of n far into metallic phase. Although their stability range decreases with n, the low-symmetry phases in metallic BaTiO(3-delta) are still retained up to an estimated concentration of n* approximately 1.9 x 10(21) cm(-3). Moreover, it appears that the itinerant electrons partially stabilize the ferroelectric phases in metallic BaTiO(3-delta) by screening strong crystal field perturbations caused by oxygen vacancies.

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