Squeeze the Shock Out: What Different Phases of Piezoelectric Materials Tell Us, a GIST Study Finds

GWANGJU, South Korea, June 28, 2021 /PRNewswire/ -- What if you could squeeze out electricity from things? Some materials, it turns out, do have this property. Piezoelectricity is the electric charge that accumulates in certain solids when mechanical stress is applied on them. Piezoelectric materials like bismuth ferrite thin films, when grown on a single lanthanum aluminate substrate give rise to highly strained epitaxial thin films that exhibit excellent electromechanical and ferroelectric properties. In bismuth ferrite thin films "doped" or polluted with lanthanum (BLFOs), piezoelectricity is attributed to the presence of "mixed-phase structures" with stripe patterns.

The formation of stripe patterns and controlling the mixed-phase structures of BLFO have been the focus of many studies over the years. But due to the ultrafast nature of phase transitions, the formation of energetically "favorable" phases under applied electric field and the origin of large electrochemical response sufficiently explored. Many scientists engaged in research on BLFO are currently plagued by the question, what does the presence of an S-polymorph, an intermediate phase, do to the properties of the material?

Researchers at the Gwangju Institute of Science and Technology (GIST) led by Prof. Ji Young Jo embarked on a journey to investigate the phase transformation dynamics of BLFO epitaxial thin films with the help of time-resolved X-ray microdiffraction. "We chose this technique because it helps us understand the electric field-induced phase transformation dynamics of the piezoelectric materials in a time scale ranging from picoseconds to microseconds," explains Prof. Jo. The results of their exploration of the piezoelectric properties of BLFO films along with the identification of the mixed-phase structures and striped patterns are published in in Acta Materialia. This paper was made available online on 21 Jan 2021 and was published in Volume 207 Issue 116683 of the journal on 1 April 2021.

BLFO can be converted into monoclinic (M_A, M_C, tilted M_C), tetragonal (T-phase), an intermediate S-phase, or mixed phases via strain engineering. The investigation into the transformation dynamics revealed that the phase changed were from M_c to S-phase were dependent on the polarity of the electric field applied. The study also concluded that the high piezoelectric response seen in mixed-phase BLFO films is due to the presence of S /S_tilt­ phases.

"Understanding the role of stripe patterns and the S-phases can help us create ultrafast piezoelectric devices with a response time of sub-microseconds," concludes Prof. Jo. The findings from this study provide us a new perspective on the use of strain engineering to design ultra-high piezoelectric thin films. This has far-reaching implications in the future of energy harvesting.

Reference

Title of original paper: The role of intermediate S-polymorph towards high piezoelectricity in La-doped BiFeO₃ epitaxial thin films
Journal: Acta Materialia
DOI: https://doi.org/10.1016/j.actamat.2021.116683

About Gwangju Institute of Science and Technology (GIST)

Gwangju Institute of Science and Technology (GIST) is a research-oriented university situated in Gwangju, South Korea. One of the most prestigious schools in South Korea, it was founded in 1993. The university aims to create a strong research environment to spur advancements in science and technology and to promote collaboration between foreign and domestic research programs. With its motto, "A Proud Creator of Future Science and Technology," the university has consistently received one of the highest university rankings in Korea.

Website: http://www.gist.ac.kr/

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Nayeong Lee
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SOURCE Gwangju Institute of Science and Technology

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