担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers  

Epitaxial rhombohedral Pb(Zr<inf>x</inf>Ti<inf>1−x</inf>)O<inf>3</inf> (PZT) thin films with different compositions (x = 0.7-0.55) were fabricated on SrRuO<inf>3</inf>/SrTiO<inf>3</inf>(111) substrates by chemical solution deposition. The domain volume fraction and lattice constants of the thin films varied systematically with the PZT composition. All films exhibited strong ferroelectricity, with remnant polarization values comparable to theoretically estimated values. The effective electro-optic (EO) coefficient (r<inf>c</inf>) was not constant with respect to the applied field but varied with the magnitude of AC field due to dynamic domain motion, reaching its maximum value at a certain electric field. The rate of change in r<inf>c</inf> due to the reversible ferroelastic domain motion, as well as the electric field at which r<inf>c</inf> peaked, were dependent on the PZT composition. These results indicate that precise control of domain structure and composition is essential to enhance the EO response of thin films.

DOI： 10.35848/1347-4065/adf4f0

Open Access

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その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/adf4f0/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We investigated the dependence of the electro-optic (EO) properties of (111)-epitaxial Hf<inf>0.5</inf>Zr<inf>0.5</inf>O<inf>2</inf> (HZO) thin films on their thickness in the range of 3-30 nm. HZO films were deposited on (La, Sr)MnO<inf>3</inf>-bufferred SrTiO<inf>3</inf>(001) substrates using pulsed laser deposition. Both the ferroelectric orthorhombic and paraelectric monoclinic phases were found to coexist in the 30 nm thick film, and the fraction of the former phase increased with the decrease in thickness down to 5 nm. Although the effective EO coefficient, r<inf>eff</inf>, remained almost unchanged down to 10 nm and decreased with a further decrease in thickness, the evident EO response was observed down to 3 nm, which agrees with the fact that HZO films can maintain ferroelectric properties down to a few monolayers in thickness. The small r<inf>eff</inf> in the HZO films with thickness below 5 nm was attributed to the stabilization of the ferroelectric rhombohedral-like phase.

DOI： 10.1063/5.0267559

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掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

The electrocaloric effect (ECE)-induced temperature change (ΔT) in (Ba, Sr)TiO3-based ferroelectrics under unipolar electric fields was analyzed from the separate contributions of the dielectric constant (ε) and remanent polarization (Pr) based on the Maxwell relation. Consideration of the contributions of both ε and Pr is particularly important in a unipolar electric field operation, such as on/off field switching used in device applications. Direct ΔT measurements were also performed based on the lock-in thermography technique to verify the accuracy of the ΔT intensity estimated by the indirect method. The indirect and direct ΔT values were largely consistent. The ΔT intensity near the peak temperature of ΔT was dominated by the Pr contribution; a large ∂Pr/∂T was necessary to increase the overall ΔT magnitude. In contrast, a large ∂ε/∂T was essential to expand the operating temperature range of ΔT at temperatures higher than the dielectric maximum temperature. Quantitative understanding of the contributions of both ε and Pr to ΔT in unipolar electric fields is expected to guide the search for materials with a superior ECE.

DOI： 10.1063/5.0259805

掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Society of Powder and Powder Metallurgy  

DOI： 10.2497/jjspm.15f-t14-02

Open Access

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

With the rapid advancement of information technology, there is a pressing need to develop ultracompact and energy-efficient thin-film-based electro-optic (EO) devices. A high EO coefficient in ferroelectric materials is crucial. However, substrate clamping can positively or negatively influence various physical properties, including the EO response of these films, thus complicating the development of next-generation thin-film-based devices. This study demonstrates that reversible dynamic domain motion, achieved through substrate clamping, significantly enhances the EO coefficient in epitaxial ferroelectric rhombohedral Pb(Zr, Ti)O<inf>3</inf> thin films, where the (111) and ( 11 1 ¯ ) domains coexist with distinct optical axes. In principle, this approach can be applied to different film-substrate systems, thereby contributing to the advancement of sophisticated EO devices based on ferroelectrics.

DOI： 10.1063/5.0244707

Web of Science

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