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Title: Emergent Low-Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO 3 Bulk Crystals [Emergent Low-Symmetry Phases with Large Property Enhancement in Ferroelectric KNbO 3 Bulk Crystals]

Abstract

The design of new or enhanced functionality in materials is traditionally viewed as requiring the discovery of new chemical compositions through synthesis. Large property enhancements may however also be hidden within already well-known materials, when their structural symmetry is deviated from equilibrium through a small local strain or field. Here, the discovery of enhanced material properties associated with a new metastable phase of monoclinic symmetry within bulk KNbO 3 is reported. This phase is found to coexist with the nominal orthorhombic phase at room temperature, and is both induced by and stabilized with local strains generated by a network of ferroelectric domain walls. While the local microstructural shear strain involved is only ≈0.017%, the concurrent symmetry reduction results in an optical second harmonic generation response that is over 550% higher at room temperature. Moreover, the meandering walls of the low-symmetry domains also exhibit enhanced electrical conductivity on the order of 1 S m -1. In conclusion, this discovery reveals a potential new route to local engineering of significant property enhancements and conductivity through symmetry lowering in ferroelectric crystals.

Authors:
 [1];  [1];  [2];  [3];  [3];  [1];  [1];  [4];  [3];  [5];  [1]
  1. Pennsylvania State Univ., University Park, PA (United States)
  2. Queen's Univ. Belfast, Northern Ireland (United Kingdom)
  3. Univ. of Texas at Austin, Austin, TX (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1418469
Grant/Contract Number:
AC02-06CH11357; DMR-1420620; DMR-1210588; DMR-1649490
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Advanced Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 31; Journal ID: ISSN 0935-9648
Publisher:
Wiley
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; conducting domain walls; ferroelectrics; low-symmetry phases; thermotropic phase boundaries

Citation Formats

Lummen, Tom T. A., Leung, J., Kumar, Amit, Wu, X., Ren, Y., VanLeeuwen, Brian K., Haislmaier, Ryan C., Holt, Martin, Lai, Keji, Kalinin, Sergei V., and Gopalan, Venkatraman. Emergent Low-Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO3 Bulk Crystals [Emergent Low-Symmetry Phases with Large Property Enhancement in Ferroelectric KNbO3 Bulk Crystals]. United States: N. p., 2017. Web. doi:10.1002/adma.201700530.
Lummen, Tom T. A., Leung, J., Kumar, Amit, Wu, X., Ren, Y., VanLeeuwen, Brian K., Haislmaier, Ryan C., Holt, Martin, Lai, Keji, Kalinin, Sergei V., & Gopalan, Venkatraman. Emergent Low-Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO3 Bulk Crystals [Emergent Low-Symmetry Phases with Large Property Enhancement in Ferroelectric KNbO3 Bulk Crystals]. United States. doi:10.1002/adma.201700530.
Lummen, Tom T. A., Leung, J., Kumar, Amit, Wu, X., Ren, Y., VanLeeuwen, Brian K., Haislmaier, Ryan C., Holt, Martin, Lai, Keji, Kalinin, Sergei V., and Gopalan, Venkatraman. 2017. "Emergent Low-Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO3 Bulk Crystals [Emergent Low-Symmetry Phases with Large Property Enhancement in Ferroelectric KNbO3 Bulk Crystals]". United States. doi:10.1002/adma.201700530.
@article{osti_1418469,
title = {Emergent Low-Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO3 Bulk Crystals [Emergent Low-Symmetry Phases with Large Property Enhancement in Ferroelectric KNbO3 Bulk Crystals]},
author = {Lummen, Tom T. A. and Leung, J. and Kumar, Amit and Wu, X. and Ren, Y. and VanLeeuwen, Brian K. and Haislmaier, Ryan C. and Holt, Martin and Lai, Keji and Kalinin, Sergei V. and Gopalan, Venkatraman},
abstractNote = {The design of new or enhanced functionality in materials is traditionally viewed as requiring the discovery of new chemical compositions through synthesis. Large property enhancements may however also be hidden within already well-known materials, when their structural symmetry is deviated from equilibrium through a small local strain or field. Here, the discovery of enhanced material properties associated with a new metastable phase of monoclinic symmetry within bulk KNbO3 is reported. This phase is found to coexist with the nominal orthorhombic phase at room temperature, and is both induced by and stabilized with local strains generated by a network of ferroelectric domain walls. While the local microstructural shear strain involved is only ≈0.017%, the concurrent symmetry reduction results in an optical second harmonic generation response that is over 550% higher at room temperature. Moreover, the meandering walls of the low-symmetry domains also exhibit enhanced electrical conductivity on the order of 1 S m-1. In conclusion, this discovery reveals a potential new route to local engineering of significant property enhancements and conductivity through symmetry lowering in ferroelectric crystals.},
doi = {10.1002/adma.201700530},
journal = {Advanced Materials},
number = 31,
volume = 29,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
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  • The design of new or enhanced functionality in materials is traditionally viewed as requiring the discovery of new chemical compositions through synthesis. Large property enhancements may however also be hidden within already well-known materials, when their structural symmetry is deviated from equilibrium through a small local strain or field. Here, the discovery of enhanced material properties associated with a new metastable phase of monoclinic symmetry within bulk KNbO3 is reported. This phase is found to coexist with the nominal orthorhombic phase at room temperature, and is both induced by and stabilized with local strains generated by a network of ferroelectricmore » domain walls. While the local microstructural shear strain involved is only approximate to 0.017%, the concurrent symmetry reduction results in an optical second harmonic generation response that is over 550% higher at room temperature. Moreover, the meandering walls of the low-symmetry domains also exhibit enhanced electrical conductivity on the order of 1 S m(-1). This discovery reveals a potential new route to local engineering of significant property enhancements and conductivity through symmetry lowering in ferroelectric crystals.« less
  • KNbO{sub 3} single crystals are often utilized for their piezoelectric and optical properties. In this study the domain configurations in as-grown single crystals were investigated using reflected light microscopy, scanning electron microscopy and atomic force microscopy. Using atomic force microscopy it was possible to image the distortion induced on the crystal surface by the domain walls and to quantify the predicted angle between (001){sub pc} planes across these walls for the cases of both 90 deg. domain walls and S walls. These features can also be imaged using the other two techniques. This direct measurement of surface distortion verifies themore » geometrical model of domain structures, and suggests that any possible strain energy considerations are minor in predicting the surface topography in the material after phase changes from the growth temperature.« less
  • Large reductions in the thermal conductivity of thermoelectrics using nanostructures have been widely demonstrated. Some enhancements in the thermopower through nanostructuring have also been reported. However, these improvements are generally offset by large drops in the electrical conductivity due to a drastic reduction in the mobility. Here, we show that large enhancements in the thermopower and electrical conductivity of half-Heusler (HH) phases can be achieved simultaneously at high temperatures through coherent insertion of nanometer scale full-Heusler (FH) inclusions within the matrix. The enhancements in the thermopower of the HH/FH nanocomposites arise from drastic reductions in the “effective” carrier concentration aroundmore » 300 K. Surprisingly, the mobility increases drastically, which compensates for the decrease in the carrier concentration and minimizes the drop in the electrical conductivity. Interestingly, the carrier concentration in HH/FH nanocomposites increases rapidly with temperature, matching that of the HH matrix at high temperatures, whereas the temperature dependence of the mobility significantly deviates from the typical T –α law and slowly decreases (linearly) with rising temperature. This remarkable interplay between the temperature dependence of the carrier concentration and mobility in the nanocomposites results in large increases in the power factor at 775 K. In addition, the embedded FH nanostructures also induce moderate reductions in the thermal conductivity leading to drastic increases in the ZT of HH(1 – x)/FH(x) nanocomposites at 775 K. By combining transmission electron microscopy and charge transport data, we propose a possible charge carrier scattering mechanism at the HH/FH interfaces leading to the observed anomalous electronic transport in the synthesized HH(1 – x)/FH(x) nanocomposites.« less