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Title: Cation–Eutectic Transition via Sublattice Melting in CuInP 2S 6/In 4/3P 2S 6 van der Waals Layered Crystals

Abstract

Single crystals of the van der Waals layered ferrielectric material CuInP 2S 6 spontaneously phase separate when synthesized with Cu deficiency. In this paper, we identify a route to form and tune intralayer heterostructures between the corresponding ferrielectric (CuInP 2S 6) and paraelectric (In 4/3P 2S 6) phases through control of chemical phase separation. We conclusively demonstrate that Cu-deficient Cu 1–xIn 1+x/3P 2S 6 forms a single phase at high temperature. We also identify the mechanism by which the phase separation proceeds upon cooling. Above 500 K both Cu + and In 3+ become mobile, while P 2S 6 4– anions maintain their structure. We therefore propose that this transition can be understood as eutectic melting on the cation sublattice. Such a model suggests that the transition temperature for the melting process is relatively low because it requires only a partial reorganization of the crystal lattice. As a result, varying the cooling rate through the phase transition controls the lateral extent of chemical domains over several decades in size. At the fastest cooling rate, the dimensional confinement of the ferrielectric CuInP 2S 6 phase to nanoscale dimensions suppresses ferrielectric ordering due to the intrinsic ferroelectric size effect. Finally, intralayer heterostructuresmore » can be formed, destroyed, and re-formed by thermal cycling, thus enabling the possibility of finely tuned ferroic structures that can potentially be optimized for specific device architectures.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [2];  [3];  [3];  [4];  [3];  [2];  [3];  [5];  [3]; ORCiD logo [3];  [2];  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Air Force Research Lab. (AFRL), Wright-Patterson AFB, OH (United States). Aerospace Systems Directorate; UES Inc., Beavercreek, OH (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
  4. Argonne National Lab. (ANL), Argonne, IL (United States). X-Ray Science Division
  5. Georgia Inst. of Technology, Atlanta, GA (United States). School of Chemical and Biomolecular Engineering
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Argonne National Lab. (ANL), Argonne, IL (United States); Air Force Research Lab. (AFRL), Wright-Patterson AFB, OH (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); US Air Force Office of Scientific Research (AFOSR); National Research Council (United States)
OSTI Identifier:
1376461
Grant/Contract Number:
AC05-00OR22725; AC02-06CH11357; 14RQ08COR
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 11; Journal Issue: 7; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 2D ferrielectric; 2D heterostructures; chalcogenides; sublattice melting; transition metal thiophosphate

Citation Formats

Susner, Michael A., Chyasnavichyus, Marius, Puretzky, Alexander A., He, Qian, Conner, Benjamin S., Ren, Yang, Cullen, David A., Ganesh, Panchapakesan, Shin, Dongwon, Demir, Hakan, McMurray, Jacob W., Borisevich, Albina Y., Maksymovych, Petro, and McGuire, Michael A. Cation–Eutectic Transition via Sublattice Melting in CuInP2S6/In4/3P2S6 van der Waals Layered Crystals. United States: N. p., 2017. Web. doi:10.1021/acsnano.7b02695.
Susner, Michael A., Chyasnavichyus, Marius, Puretzky, Alexander A., He, Qian, Conner, Benjamin S., Ren, Yang, Cullen, David A., Ganesh, Panchapakesan, Shin, Dongwon, Demir, Hakan, McMurray, Jacob W., Borisevich, Albina Y., Maksymovych, Petro, & McGuire, Michael A. Cation–Eutectic Transition via Sublattice Melting in CuInP2S6/In4/3P2S6 van der Waals Layered Crystals. United States. doi:10.1021/acsnano.7b02695.
Susner, Michael A., Chyasnavichyus, Marius, Puretzky, Alexander A., He, Qian, Conner, Benjamin S., Ren, Yang, Cullen, David A., Ganesh, Panchapakesan, Shin, Dongwon, Demir, Hakan, McMurray, Jacob W., Borisevich, Albina Y., Maksymovych, Petro, and McGuire, Michael A. 2017. "Cation–Eutectic Transition via Sublattice Melting in CuInP2S6/In4/3P2S6 van der Waals Layered Crystals". United States. doi:10.1021/acsnano.7b02695.
@article{osti_1376461,
title = {Cation–Eutectic Transition via Sublattice Melting in CuInP2S6/In4/3P2S6 van der Waals Layered Crystals},
author = {Susner, Michael A. and Chyasnavichyus, Marius and Puretzky, Alexander A. and He, Qian and Conner, Benjamin S. and Ren, Yang and Cullen, David A. and Ganesh, Panchapakesan and Shin, Dongwon and Demir, Hakan and McMurray, Jacob W. and Borisevich, Albina Y. and Maksymovych, Petro and McGuire, Michael A.},
abstractNote = {Single crystals of the van der Waals layered ferrielectric material CuInP2S6 spontaneously phase separate when synthesized with Cu deficiency. In this paper, we identify a route to form and tune intralayer heterostructures between the corresponding ferrielectric (CuInP2S6) and paraelectric (In4/3P2S6) phases through control of chemical phase separation. We conclusively demonstrate that Cu-deficient Cu1–xIn1+x/3P2S6 forms a single phase at high temperature. We also identify the mechanism by which the phase separation proceeds upon cooling. Above 500 K both Cu+ and In3+ become mobile, while P2S64– anions maintain their structure. We therefore propose that this transition can be understood as eutectic melting on the cation sublattice. Such a model suggests that the transition temperature for the melting process is relatively low because it requires only a partial reorganization of the crystal lattice. As a result, varying the cooling rate through the phase transition controls the lateral extent of chemical domains over several decades in size. At the fastest cooling rate, the dimensional confinement of the ferrielectric CuInP2S6 phase to nanoscale dimensions suppresses ferrielectric ordering due to the intrinsic ferroelectric size effect. Finally, intralayer heterostructures can be formed, destroyed, and re-formed by thermal cycling, thus enabling the possibility of finely tuned ferroic structures that can potentially be optimized for specific device architectures.},
doi = {10.1021/acsnano.7b02695},
journal = {ACS Nano},
number = 7,
volume = 11,
place = {United States},
year = 2017,
month = 7
}

Journal Article:
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  • In this paper, we explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP 2S 6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleavedmore » bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 V—likely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. Finally, the existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties that are presently not found in any members of the growing “graphene family”.« less
  • In this paper, we report on polarization switching properties of thin flakes of van der Waals ferrielectric CuInP 2S 6. We observe mesoscale polarization domains, ferroelectric switching, and the Curie temperature above 299 K down to a thickness of ~50 nm. However, the electromechanical response is progressively suppressed below 50 nm, and vanishes at room temperature at a thickness of ~10 nm. Though larger than a single layer, 10 nm is still a very small value compared to the expectations for an intrinsic ferroelectric semiconductor. We therefore propose a model for a doped surface layer that screens spontaneous polarization inmore » this material. The charges in the screening layer may also participate in secondary chemical reactions, which may explain domain pinning observed in thermal cycling of the flakes above the Curie temperature. At the same time, ferroelectric switching is intertwined with ionic diffusion, resulting in erratic and damaging switching at room temperature. Finally, owing to much stronger temperature dependence of ionic diffusion, the two phenomena can be decoupled allowing more reliable switching to be obtained at low temperatures.« less
  • CrCl 3 is a layered insulator that undergoes a crystallographic phase transition below room temperature and orders antiferromagnetically at low temperature. Weak van der Waals bonding between the layers and ferromagnetic in-plane magnetic order make it a promising material for obtaining atomically thin magnets and creating van der Waals heterostructures. In this work we have grown crystals of CrCl 3, revisited the structural and thermodynamic properties of the bulk material, and explored mechanical exfoliation of the crystals. We find two distinct anomalies in the heat capacity at 14 and 17 K confirming that the magnetic order develops in two stagesmore » on cooling, with ferromagnetic correlations forming before long-range antiferromagnetic order develops between them. This scenario is supported by magnetization data. A magnetic phase diagram is constructed from the heat capacity and magnetization results. We also find an anomaly in the magnetic susceptibility at the crystallographic phase transition, indicating some coupling between the magnetism and the lattice. First-principles calculations accounting for van der Waals interactions also indicate spin-lattice coupling, and find multiple nearly degenerate crystallographic and magnetic structures consistent with the experimental observations. Lastly, we demonstrate that monolayer and few-layer CrCl 3 specimens can be produced from the bulk crystals by exfoliation, providing a path for the study of heterostructures and magnetism in ultrathin crystals down to the monolayer limit.« less