Two "X"-shaped {Eu6}-embedded water-soluble heterometallic polyoxotungstates based on {Eu6M4WSe4(GeW10)4} (M = Cr, Al) clusters with resistance-switching

Abstract

Two water-soluble 3D tungstogermanate frameworks H₁₇Na₄K₇(H₂O)₁₂[Eu₆(H₂O)₄Cr₄(WO₆)(SeO₃)₄(GeW₁₀O₃₇)₂ (GeW₁₀O₃₈)₂]·32H₂O (1-EuCr) and H₁₇Na₂K₉(H₂O)₁₄[Eu₆(H₂O)₄ Al₄(WO₆)(SeO₃)₄(GeW₁₀O₃₇)₂(GeW₁₀O₃₈)₂]·32H₂O (2-EuAl) are constructed from unprecedented heterometallic {Eu₆(H₂O)₄M₄(WO₆)(SeO₃)₄(GeW₁₀O₃₇)₂(GeW₁₀O₃₈)₂} ({Eu₆M₄WSe₄(GeW₁₀)₄}, M = Cr for 1-EuCr; Al for 2-EuAl) clusters with unique “X”-shaped {Eu₆} cores. Both 1-EuCr and 2-EuAl exhibit stable non-volatile storage behavior and rewritable resistive switching with high ON/OFF ratios of 1.73 × 10⁴ (1-EuCr) and 1.53 × 10³ (2-EuAl), respectively, and excellent stabilities over 58 cycles. The high switching ratio of 1-EuCr is attributed to the metastable redox properties of Cr³⁺. To the best of our knowledge, this work presents the first report of electrical bistable devices based on Eu-Cr/Eu-Al heterometallic POMs, offering new material candidates and valuable design guidelines for the development of high-switching-ratio electrical bistable devices.