Abstract
In Ba0.6Sr0.4TiO3 (BSTO)‐based epitaxial nanocomposite films increased P r values are demonstrated by up to a factor of 3 compared to standard BSTO films. A strongly reduced temperature coefficient of polarization retention is also obtained, i.e., 0.07% °C−1 compared to 0.24% °C−1. Piezopoling with only marginal leakage current is also achieved up to 200 °C, the highest temperature studied. The origin of the improved performance is the incorporation of Sm2O3 nanopillars in the films which acted as stiff vertical nanoscaffolds, inducing a strong tetragonal distortion in the BSTO (up to 1.033(7) in terms of the out‐of‐plane/in‐plane lattice dimensions). The films have comparable performance to industry‐standard Pb(Zr,Ti)O3 films, at the same time as being Pb‐free.
Highlights
A paradigm shift in ferroelectrics towards miniaturization has come about because of the considerable interest in low energy consumption and non-volatile nanoelectronics
The x = 0.75 film was found to be the optimum composition for enhanced polarization owing to the greatest induced tetragonal distortion of the BSTO.[2, 9]
A systematic coherent tensile strain tuning in the vertical direction is achieved.[2]
Summary
A paradigm shift in ferroelectrics towards miniaturization has come about because of the considerable interest in low energy consumption and non-volatile nanoelectronics. When the lateral and vertical dimensions of (Ba,Sr)TiO3 and BaTiO3 are downscaled to below 26 nm in vertical thickness, or below 20 nm in nanowire lateral dimension, their functional properties are degraded compared to the bulk.[6,7] On the other hand, using vertically aligned nanocomposites films (of BaTiO3-Sm2O3 and Ba0.6Sr0.4TiO3-Sm2O3 compositions) containing lateral nanoscale features of sizes down to 10 nm, we have shown that size-limited property degradation is eliminated.[8,9] A key reason for this is that the interfaces of the ferroelectric nanostructures in the films are epitaxially coupled to a second scaffold phase in the film In such films, there is strong vertical strain that causes a strong enhancement of Curie temperature,[8,9] enhanced dielectric tunability, reduced dielectric loss and leakage current[9] and, enhanced saturation polarization.[2] On the other hand, in these promising nanocomposite ferroelectrics neither has the extent of polarization nor has the polarization retention been systematically studied. SmO is a cubic, non-polarizable phase with significantly greater stiffness (125 - 220 GPa) than BSTO (~80 GPa).[10,11,12]
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