Origin of giant negative piezoelectricity in a layered van der Waals ferroelectric

Lu You; Yang Zhang; Shuang Zhou; Apoorva Chaturvedi; Samuel A Morris; Fucai Liu; Lei Chang; Daichi Ichinose; Hiroshi Funakubo; Weijin Hu; Tom Wu; Zheng Liu; Shuai Dong; Junling Wang

doi:10.1126/sciadv.aav3780

Origin of giant negative piezoelectricity in a layered van der Waals ferroelectric

Sci Adv. 2019 Apr 19;5(4):eaav3780. doi: 10.1126/sciadv.aav3780. eCollection 2019 Apr.

Authors

Lu You^{1

2}, Yang Zhang³, Shuang Zhou^{1

4}, Apoorva Chaturvedi¹, Samuel A Morris¹, Fucai Liu^{1

5}, Lei Chang¹, Daichi Ichinose⁶, Hiroshi Funakubo⁶, Weijin Hu⁷, Tom Wu⁸, Zheng Liu¹, Shuai Dong³, Junling Wang¹

Affiliations

¹ School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
² School of Physical Science and Technology, Soochow University, 1 Shizi Street, Suzhou 215006, China.
³ School of Physics, Southeast University, Nanjing 211189, China.
⁴ School of Science, Nanjing University of Posts and Telecommunications, Nanjing 210023, China.
⁵ School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu, China.
⁶ School of Materials and Chemical Technology, Department of Material Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan.
⁷ Shenyang National Laboratory for Materials Science, Institute of Metal Research (IMR), Chinese Academy of Sciences (CAS), Shenyang 110016, China.
⁸ School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia.

Abstract

Recent research on piezoelectric materials is predominantly devoted to enhancing the piezoelectric coefficient, but overlooks its sign, largely because almost all of them exhibit positive longitudinal piezoelectricity. The only experimentally known exception is ferroelectric polymer poly(vinylidene fluoride) and its copolymers, which condense via weak van der Waals (vdW) interaction and show negative piezoelectricity. Here we report quantitative determination of giant intrinsic negative longitudinal piezoelectricity and electrostriction in another class of vdW solids-two-dimensional (2D) layered ferroelectric CuInP₂S₆. With the help of single crystal x-ray crystallography and density-functional theory calculations, we unravel the atomistic origin of negative piezoelectricity in this system, which arises from the large displacive instability of Cu ions coupled with its reduced lattice dimensionality. Furthermore, the sizable piezoelectric response and negligible substrate clamping effect of the 2D vdW piezoelectric materials warrant their great potential in nanoscale, flexible electromechanical devices.