Insights into high electric-field-induced strain in BiAlO₃ modified Bi_1/2Na_1/2TiO₃ films

Muhammad Sheeraz^{¹^,^†}, Sung Sik Won^{²^,^†}, Jong Pil Kim^³, Sabir Ali^⁴, Fazli Akram^⁵, Hyoung-Su Han^⁶, Bong Chan Park^¹, Tae Heon Kim^{¹^,⁷}, Ill Won Kim^¹, Aman Ullah^⁴(), Chang Won Ahn^¹()

1Department of Physics and Energy Harvest Storage Research Center (EHSRC), University of Ulsan, Ulsan 44610, Republic of Korea

2Research Center, Kairos Co., Ltd., Suwon 16229, Republic of Korea

3Busan Center, Korea Basic Science Institute, Busan 46742, Republic of Korea

4Department of Physics, University of Science and Technology, Bannu 28100, Pakistan

5Center for High Technology Materials and the Department of Mechanical Engineering, The University of New Mexico, Albuquerque 87131, USA

6School of Materials Science and Engineering, University of Ulsan, Ulsan 44776, Republic of Korea

7Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea

^† Muhammad Sheeraz and Sung Sik Won contributed equally to this work.

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Abstract

The development of high-strain piezoelectric materials has presented a longstanding challenge, particularly in the development of high-strain polycrystalline lead-free piezoelectric thin films. In this work, we present a strategy for customizing the electrostrain in lead-free thin films through phase transition engineering. In this study, we achieved a high recoverable electrostrain in a Bi_1/2Na_1/2TiO₃–BiAlO₃ (BNT–BA) film. To accomplish this, ferroelectric BNT and BNT–BA films with identical thicknesses of 500 nm were fabricated on Pt(111)/TiO₂/SiO₂/Si(100) substrates via a sol-gel method. Compared with the BNT film, the BNT–BA film exhibited a greater polarization response and superior field strength endurance, maintaining the energy storage density beyond the breakdown field strength of the BNT. The BNT–BA film demonstrated a large unipolar strain of S = 0.43% with a normalized strain (maximum strain/maximum applied electric field (S_max/E_max)) of 203 pm/V, followed by an effective transverse piezoelectric coefficient ( $e_{31, f}^{*}$ ) of ~2.48 C/m², which was more than two times greater than the value obtained for BNT (i.e., maximum strain/maximum applied electric field (S_max/E_max) = 72 pm/V and $e_{31, f}^{*}$ of ~1.09 C/m²). This high strain response in the BNT–BA film can be attributed to the electric-field-induced phase transition of the mixed (i.e., cubic and rhombohedral) phases into rhombohedral and tetragonal phases (mainly the rhombohedral structure), which recover back to the original state when the electric field is removed. These findings suggest new pathways for achieving significant strain levels via alternative mechanisms, potentially enhancing the effectiveness and expanding the applications of piezoelectric materials.

Keywords

electrostrain piezoelectrics Bi_1/2Na_1/2TiO₃ (BNT)BiAlO₃ (BA)thin films phase transition

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References

[1]

Jaffe B, Cook WR, Jaffe HL. Piezoelectric Ceramics. London (UK): Academic Press, 1971

Crossref

[2]

Waqar M, Wu HJ, Chen JS, et al. Evolution from lead-based to lead-free piezoelectrics: Engineering of lattices, domains, boundaries, and defects leading to giant response. Adv Mater 2022, 34: 2106845.

Insights into high electric-field-induced strain in BiAlO3 modified Bi1/2Na1/2TiO3 films