A Promising Phase Change Material with Record High Ionic Conductivity over a Wide Temperature Range of a Plastic Crystal Phase and Magnetic Thermal Memory Effect

Abstract

The emerging organic ion plastic crystals (OIPCs) are the most promising candidates used as solid-state electrolytes in a range of ionic devices. To endow an OIPC with additional functionality may create a new type of material for multifunctional devices. Herein, we present an ion plastic crystal, [EMIm]­[Ni­(mnt)2] (1; [EMIm]+ = 1-ethyl-3-methylimidazolium and mnt2– = maleonitriledithiolate), and its crystal consists of twin dimeric chains of [Ni­(mnt)2]− anions, embraced by [EMIm]+ cations. A crystal-to-plastic crystal transformation with a large latent heat that occurred at ∼367/337 K on heating/cooling is confirmed by the differential scanning calorimetry (DSC) technique. The plastic crystal phase in 1, characterized by variable temperature powder X-ray diffraction (PXRD) and optical microscopy images, spans a broad temperature range with ΔT ∼123/153 K on heating/cooling (DSC measurement), and the wide ΔT is relevant to an extra stable anion chain owing to the strong antiferromagnetic (AFM) interactions protecting the chain from collapse in the plastic crystal state. 1 is a single-component ion plastic crystal with a record high ion conductivity, 0.21 S·cm–1, at 453 K. The crystal-to-plastic crystal transformation in 1 is coupled to a bistable magnetic transition to give a multi-in-one multifunctional material. This study provides a creative thought for the design of OIPCs with striking thermal, electrical, and magnetic multifunctionality.

Two Ongoing Magnetic Transitions Originating from Spin-Peierls Dimerization and Cation Orientation Transformation in an S = 1/2 Spin Chain System

“…In the moiety of the DMPy + cation, the five-membered ring of pyrrolidinium shows a puckered configuration, where the N5 atom is located out-of-plane of the pyrrolidinium ring and the plane consisting of N5, C13, and C14 atoms of two methyl groups are almost perpendicular to the pyrrolidinium ring. The bond lengths and angles in the [Ni­(mnt) 2 ] − anion and DMPy + cation at 223 K, summarized in Table S2, are comparable to those in the reported [Ni­(mnt) 2 ] − and DMPy + salts, respectively.…”

Magnetic bistable organic ionic plastic crystal with room temperature ion conductivity comparable to NASICON and superionic conduction in a broad temperature window

“…The reported high ionic conducting plastic crystals are summarized in Table S8 (ESI †), and compared with them, 1 shows the highest recorded ionic conductivity in the plastic phase. 18,25,32,[35][36][37][38][39][40][41][42][43][44][45][46][47][48] The activation energy of ion migration is estimated according to the Arrhenius equation,…”

“…11,17,[20][21][22][23][24] We aim to seek multifunctional superionic conducting OIPCs. To this end, in previous study, we proposed a strategy for the design of a new type of OIPCs, 25 i.e., to achieve OIPCs by combining metal bis-1,2-dithiolene ([M(dithiolato) 2 ] À anion; M = Ni, Pd, or Pt ion) with conventional globular-shaped cations, because the negative charge is distributed on the whole molecule skeleton in a planar p-electron delocalized [M(dithiolato) 2 ] À anion, minimizing interionic Coulomb interactions, which reduces both the lattice energy and rotational barrier of spherical cations. Moreover, this strategy may offer the OIPCs magnetic bistability, 19,24,26,27 owing to S = 1 2 [M(dithiolato) 2 ] À anions preferring to form columnar stacks wherein the strong spin-lattice interplays promote spin-Peierls-type transition; besides this, the columnar anion stacks also provide robust frameworks owing to strong antiferromagnetic (AFM) couplings in a stack, which are beneficial for ion migration and improve the disadvantage of multiple plastic crystal phases in the conventional 'discrete' ion plastic crystals as well.…”

“…Moreover, this strategy may offer the OIPCs magnetic bistability, 19,24,26,27 owing to S = 1 2 [M(dithiolato) 2 ] À anions preferring to form columnar stacks wherein the strong spin-lattice interplays promote spin-Peierls-type transition; besides this, the columnar anion stacks also provide robust frameworks owing to strong antiferromagnetic (AFM) couplings in a stack, which are beneficial for ion migration and improve the disadvantage of multiple plastic crystal phases in the conventional 'discrete' ion plastic crystals as well. 25 Herein, we report the third member in this new type of OIPC family, [DEIm][Ni(mnt) 2 ] (1), with two-step solid-solid phase transitions prior to melting, i.e., crystal-crystal transformation in the lower temperature region coupled with magnetic bistability and negative thermal expansion; crystal-plastic crystal phase transition in the higher temperature regime. Most strikingly, 1 exhibits record room temperature ion conduction (s = 4.46 Â 10 À4 S cm À1 ) for the as-prepared crystals, comparable to the room temperature fast ion conductor NASICON (Na 3 Zr 2 Si 2 PO 12 ), and superionic conduction with a broad temperature window (s = 0.19-0.94 S cm À1 in 318-368 K for the annealed crystals and s E 1.77 S cm À1 in 408-453 K in the plastic crystal state).…”

Ultrafast femtosecond pressure modulation of structure and exciton kinetics in 2D halide perovskites for enhanced light response and stability

“…XRD and XPS were characterized by the light and humid thermal stability of perovskite. The phase transition and decomposition of (F-PEA) 2 PbI 4 PSCs were analyzed by differential scanning calorimetry (DSC) under the nitrogen atmosphere 52 (Supplementary Fig. 26 ).…”