Piezoelectric domain walls in van der Waals antiferroelectric CuInP2Se6

Abstract

Polar van der Waals chalcogenophosphates exhibit unique properties, such as negative electrostriction and multi-well ferrielectricity, and enable combining dielectric and 2D electronic materials. Using low temperature piezoresponse force microscopy, we revealed coexistence of piezoelectric and non-piezoelectric phases in CuInP 2 Se 6 , forming unusual domain walls with enhanced piezoelectric response. From systematic imaging experiments we have inferred the formation of a partially polarized antiferroelectric state, with inclusions of structurally distinct ferrielectric domains enclosed by the corresponding phase boundaries. The assignment is strongly supported by optical spectroscopies and density-functionaltheory calculations. Enhanced piezoresponse at the ferrielectric/antiferroelectric phase boundary and the ability to manipulate this entity with electric field on the nanoscale expand the existing phenomenology of functional domain walls. At the same time, phase-coexistence in chalcogenophosphates may lead to rational strategies for incorporation of ferroic functionality into van der Waals heterostructures, with stronger resilience toward detrimental size-effects.

Inverse Domain‐Size Dependence of Piezoelectricity in Ferroelectric Crystals

“…Moreover, the strategy to tune macroscopic piezoelectricity by controlling the intrinsic polarization rotation applies to principally all types of ferroelectric materials including organometal halide perovskites, [ 38 ] metal‐free molecular ferroelectrics, [ 39 ] lead‐free piezoceramics, [ 40 ] textured ferroelectric ceramics, [ 41 ] and 2D ferroelectrics. [ 42 ] Some potential examples for the experimental design of new materials utilizing the inverse‐domain size effect to achieve enhanced piezoelectric properties are presented in Note S3 (Supporting Information). The theoretical approach based on thermodynamic analysis and phase‐field modeling may stimulate further interest in understanding the microstructural size effects for other ferroic and multiferroic materials such as ferromagnetic shape memory alloys.…”

Two-dimensional ferroelasticity in van der Waals β’-In2Se3

“…The intrinsically weak interlayer interaction allows each individual layer to behave independently, granting the unique opportunity to preserve bulk properties down to single-layer thickness 5 – 7 . Various two-dimensional (2D) functionalities have been discovered in vdW materials 7 , including superconductivity 8 – 10 , ferromagnetism 11 , 12 , ferroelectricity 13 – 17 and antiferroelectricity 18 , 19 , offering a wealth of choices for making ultrathin flexible 2D heterostructure devices 7 , 20 . Among all the ferroic properties, ferroelasticity represents the mechanical equivalent of ferromagnetism and ferroelectricity, with multiple orientation states of spontaneous lattice strain that are switchable under mechanical stimuli 4 , 21 , 22 .…”

Anisotropic Ion Migration and Electronic Conduction in van der Waals Ferroelectric CuInP2S6

“…The rapid growth of two-dimensional (2D) semiconductor devices has spurred burgeoning interest in searching for functional dielectrics that can be integrated with 2D materials like graphene and transition-metal dichalcogenides (TMDs) for device performance enhancement and engineering-rich functionalities. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Copper indium thiophosphate CuInP 2 S 6 (CIPS), one of the van der Waals (vdW) ferroelectrics from the transitional metal thio/seleno-phosphates (TPS) family, allows such interface integration to build full-vdW heterostructure based functional logic and memory devices, such as negative capacitance field-effect transistors (NC-FETs), 21 ferroelectric tunnel junctions (FTJs), 22,23 and ferroelectric field-effect transistors (Fe-FETs). 5,10,11 In these devices, the local response of CIPS to the electric field is thus of paramount importance to determine the device performance.…”