Exploring the role of viologen and iodocuprate in the enhanced resistive switching performance of Anderson polyoxometalate-based three-component hybrids

Abstract

Polyoxometalate (POM)-based materials are ideal candidates for implementing molecular memories, and rational POM molecule design is key to higher resistive switching (RS) performance. In this work, in order to obtain a deep structure–property correlation of POM-based memristors, three Anderson-based hybrids, i.e. two-component hybrids (MV)₃(MnMo₆O₁₈L₂)₂·4DMF (1) and (MV)₂[Cu(DMF)₂](MnMo₆O₁₈L₁)₂·6DMF (2), and the three-component one (MV)₂(Cu₂I₃)(MnMo₆O₁₈L₂)·4CH₃CN (3) (L = 2-(hydroxymethyl)-2-(pyridine-4-yl)-1,3-propanediol) have been structurally determined. These hybrids together with the precursors (methyl viologen (MV²⁺), CuI, and (MnMo₆O₁₈L₂)) were further fabricated as memristors with the structure of ITO/active layer/Ag. Interestingly, three precursors are RS silent or have bad RS performance, but the incorporation of MV²⁺ in 1 and 2 can trigger the RS performances, and the further decoration of iodocuprate in 3 can render enhanced RS behavior (ON/OFF ratio: 2.32 × 10²) with high thermal-tolerance temperature (240 °C) and extremely long-term stability. The RS mechanism could be assigned to the valence change (VC) induced by oxygen vacancy migrations. The presence of air-stable (MnMo₆O₁₈L₂)³⁻-MV²⁺ donor–acceptor couples can stabilize the oxygen vacancies, which not only trigger the RS behaviors in ITO/1/Ag and ITO/2/Ag, but also result in extremely long-term stability in ITO/3/Ag. Besides, the oxygen vacancies can also be stabilized by Cu₂I₃ with intense cuprophilic interactions, which corresponds to enhanced RS properties in ITO/3/Ag. This mechanism could be validated by the following structural characters in 3: the stronger POM-MV²⁺ interactions, the better planarity of MV²⁺, the very short Cu⋯Cu distances and the ABAB-type packing fashion. The structure–property correlation in this work can provide a new strategy for the development of highly efficient and reliable memristors.