Abstract
The interest in ferroelectric van der Waals crystals arises from the potential to realize ultrathin ferroic systems owing to the reduced surface energy of these materials and the layered structure that allows for exfoliation. Here, we quantitatively unravel giant negative electrostriction of van der Waals layered copper indium thiophosphate (CIPS), which exhibits an electrostrictive coefficient Q33 as high as -3.2m4/C2 and a resulting bulk piezoelectric coefficient d33 up to -85 pm/V. As a result, the electromechanical response of CIPS is comparable in magnitude to established perovskite ferroelectrics despite possessing a much smaller spontaneous polarization of only a few μC/cm2. In the paraelectric state, readily accessible owing to low transition temperatures, CIPS exhibits large dielectric tunability, similar to widely used barium strontium titanate, and as a result both giant and continuously tunable electromechanical response. The persistence of electrostrictive and tunable responses in the paraelectric state indicates that even few-layer films or nanoparticles will sustain significant electromechanical functionality, offsetting the inevitable suppression of ferroelectric properties in the nanoscale limit. These findings can likely be extended to other ferroelectric transition metal thiophosphates and (quasi-) two-dimensional materials, and might facilitate the quest toward alternative ultrathin functional devices incorporating electromechanical response.
| Original language | English |
|---|---|
| Article number | 024401 |
| Journal | Physical Review Materials |
| Volume | 3 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 1 2019 |
Funding
Data interpretation, manuscript preparation, sample synthesis, and x-ray spectroscopy were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering division. Part of the experiment design, analysis, and interpretation were sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy. PFM experiments, analysis, and analysis of theoretical calculations were conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility (CNMS2017-R49) and enabled by a research grant from the Science Foundation (SFI) under the U.S.-Ireland R&D Partnership Programme Grant No. SFI/14/US/I3113. The tunability data analysis framework was supported by the CICECO-Aveiro Institute of Materials (Ref. No. FCTUID/CTM/50011/2013) financed by national funds through the FCT/MEC and, when applicable, cofinanced by FEDER under the PT2020 Partnership Agreement. DFT calculations were supported by DOE Grant No. DE-FG02-09ER46554 and by the McMinn Endowment at Vanderbilt University and the U.S. Department of Defense. Calculations were performed at the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Manuscript preparation was partially funded by the Air Force Research Laboratory under an Air Force Office of Scientific Research grant (LRIR Grant No. 14RQ08COR) and a grant from the National Research Council. We thank Lane W. Martin, Gabriel Velarde, and Josh Agar for providing a reference film of that was employed here for comparison of piezoelectric performance.