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Giant polarization in super-tetragonal thin films through interphase strain

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Science  03 Aug 2018:
Vol. 361, Issue 6401, pp. 494-497
DOI: 10.1126/science.aan2433

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An epitaxial route to strain

Strain can have a dramatic effect on the properties of materials. Zhang et al. introduced a large strain in the material PbTiO3 by growing it epitaxially in a composite with PbO. On the boundaries between the two materials, their normally different lattice constants were matched, giving rise to the strain. As a consequence, the films exhibited a very large electric polarization even in the absence of an electric field. The method may be applicable to generating other functional materials.

Scence, this issue p. 494

Abstract

Strain engineering has emerged as a powerful tool to enhance the performance of known functional materials. Here we demonstrate a general and practical method to obtain super-tetragonality and giant polarization using interphase strain. We use this method to create an out-of-plane–to–in-plane lattice parameter ratio of 1.238 in epitaxial composite thin films of tetragonal lead titanate (PbTiO3), compared to 1.065 in bulk. These thin films with super-tetragonal structure possess a giant remanent polarization, 236.3 microcoulombs per square centimeter, which is almost twice the value of known ferroelectrics. The super-tetragonal phase is stable up to 725°C, compared to the bulk transition temperature of 490°C. The interphase-strain approach could enhance the physical properties of other functional materials.

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