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Proceedings Paper

Pyro-paraelectricity: a new effect in hetergeneous material architectures
Author(s): Huai-An Chin; Sheng Mao; Bhadrinarayana L. Visweswaran; Kwaku K. Ohemeng; Sigurd Wagner; Prashant K. Purohit; Michael C. McAlpine
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Paper Abstract

The electrical responses of materials and devices subjected to thermal inputs, such as the Seebeck effect and pyroelectricity, are of great interest in thermal-electric energy conversion applications. Of particular interest are phenomena which exploit heterogeneities in the mechanics of heterostructured materials for novel and unexplored mechanisms in thermal-electric conversion. Here we introduce a new and universal mechanism for converting thermal stimuli into electricity via structural heterogeneities, which we term “pyro-paraelectricity.” Specifically, when a paraelectric material is grown on a substrate with a different lattice constant, the paraelectric layer experiences an inhomogeneous strain due to the lattice mismatch, establishing a strain gradient along the axis of the layer thickness. This induced strain gradient can be multiple orders of magnitude higher than strain gradients in bulk materials imparted by mechanical bending (0.1 m-1). Consequently, charge separation is induced in the paraelectric layer via flexoelectricity, leading to a polarization in proportion to the dielectric constant. The dielectric constant, and thus the polarization, changes with temperature. Therefore, when a strained metal-insulator-metal (MIM) heterostructure is subjected to a thermal input, changes in the permittivity generate an electrical response. We demonstrate this mechanism by employing a MIM heterostructure with a high permittivity sputtered barium strontium titanate (BST) film as the insulating layer in a platinum sandwich. The resulting strain gradient of more than 104 m-1, an enhancement of five orders of magnitude due to the structural heterogeneity, was verified by an X-ray diffraction scan. With an applied thermal input, the strained MIM heterostructure generated current which was highly correlated to the thermal input. A theoretical model was found to be consistent with the experimental data. These results demonstrate the existence of “pyro-paraelectricity,” a flexoelectricity-mediated mechanism for thermal-electrical conversion.

Paper Details

Date Published: 27 March 2015
PDF: 11 pages
Proc. SPIE 9439, Smart Materials and Nondestructive Evaluation for Energy Systems 2015, 94390E (27 March 2015); doi: 10.1117/12.2083644
Show Author Affiliations
Huai-An Chin, Princeton Univ. (United States)
Sheng Mao, Univ. of Pennsylvania (United States)
Bhadrinarayana L. Visweswaran, Princeton Univ. (United States)
Kwaku K. Ohemeng, Princeton Univ. (United States)
Sigurd Wagner, Princeton Univ. (United States)
Prashant K. Purohit, Univ. of Pennsylvania (United States)
Michael C. McAlpine, Princeton Univ. (United States)

Published in SPIE Proceedings Vol. 9439:
Smart Materials and Nondestructive Evaluation for Energy Systems 2015
Norbert G. Meyendorf, Editor(s)

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