Relaxor Ferroelectric Ca-Doped (K,Na,Li)NbO3 Single-Crystal Microcubes with Suppressed Defects and Tunable Symmetry for Flexible High-Power Capacitors

초록

Single-crystal relaxor ferroelectrics (RFEs) offer high polarization, slim hysteresis, and superior breakdown strength, making them ideal for advanced dielectric energy storage. However, scalable synthesis of lead-free single crystals remains challenging. Here, a molten-salt strategy is employed to synthesize Ca-doped (K0.432Na0.528Li0.04)(1-x)Ca4x/3Nb1-x/3O3 (KNLN-xCa, x = 0, 0.01, and 0.03) single-crystal microcubes with tunable crystal symmetry and defect concentration. The KNLN-0.01Ca single-crystal exhibits relaxor behavior with a recoverable energy density of 2.66 J cm(-3) and an efficiency of 78.7% at 100 kV cm(-1). In contrast, the ceramic counterpart shows classical ferroelectric features, highlighting the critical role of the crystallization pathway. Dislocation-driven nanodomain formation during oriented attachment is identified as the primary mechanism inducing relaxor behavior, independent of chemical disorder. Incorporation of the KNLN-0.01Ca microcubes into a polydimethylsiloxane (PDMS) matrix produces a flexible composite capacitor with a breakdown strength of 350 kV cm(-1), a recoverable energy density of 5.76 J cm(-3), and an efficiency of 88%. Under pulsed discharge conditions, the device delivers a discharge energy density of 1.4 J cm(-3) with a fast discharge time (approximate to 20 ns) and high-power density (70 MW cm(-3)). These findings demonstrate a crystallographically engineered, defect-modulated, and process-scalable route to high-performance, lead-free RFEs for next-generation flexible energy storage devices.

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