Giant negative electrostriction and dielectric tunability in a van der Waals layered ferroelectric

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 -3.2 m 4 /C 2 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/cm 2 . 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 3 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 towards novel ultrathin functional devices incorporating electromechanical response.

Fast Scanning Probe Microscopy via Machine Learning: Non‐Rectangular Scans with Compressed Sensing and Gaussian Process Optimization

“…[ 70 ] Further details concerning the ferroelectric properties of CIPS can be found elsewhere. [ 69,71–74 ] Nevertheless, CIPS with feature sizes spanning orders of magnitude is an excellent basis for testing sparse data reconstruction.…”

Locally Controlled Cu-Ion Transport in Layered Ferroelectric CuInP2S6

“…1,9 Just above the ferroelectric transition temperature, giant electrostriction -a signature property of CIPS -is preserved, and the lattice, therefore, exhibits pronounced field-induced and continuously-tunable expansion. 10 It is also known, from macroscopic measurements, that CIPS attains significant ionic conductivity. 11 Because of this, thiophosphates featuring the [P 2 S 6 ] 4anion are also considered as solid electrolyte for Li-and Na-ion batteries.…”

The Concept of Negative Capacitance in Ionically Conductive Van der Waals Ferroelectrics

“…The calculated piezoelectric constants for the two polar phases enabled the experimental verification of these phases by piezoresponse force microscopy (PFM) measurements of the piezoelectric constants. Moreover, the material also exhibits giant negative electrostrictive coefficients, [24,29] which is a direct consequence of the highly anharmonic potential well. [28] In addition, CIPS has a high Cu-ion conductivity that extends into the temperature range of the ferroelectric phase.…”