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|Giant piezoelectric response (d33) in (K0.45Na0.55)0.96Li0.04NbO3 lead-free single crystals|
|Keywords: Giant piezoelectric response, Lead-free, KNN single crystal|
|Piezoelectric materials have attracted much attention due to their practical application in sensors, actuators, ultrasonic transducers, etc. However, the widely used piezoelectric materials are lead-containing, which raises environmental concerns during their preparation, processing, and disposal. Therefore, it is urgent to develop lead-free piezoelectric materials. Among these lead-free alternatives, potassium sodium niobate (KNN) is one of the most outstanding candidates due to its good piezoelectric performance. Piezoelectric single crystals usually have better electrical properties than their ceramics counterparts. Therefore, it is plausible to further enhance their electrical properties by preparing KNN-based single crystals. Solid-state crystal growth (SSCG) method is a newly developed single crystal growth method. In this method, a single crystal seed is tightly bonded to the polycrystalline ceramic matrix, and annealed at a high temperature below the melting point. The single crystal will finally be grown by consuming the matrix. It is found that the seed is a key factor for crystal growth. For KNN, only KTaO3 crystal seed was found to be suitable for SSCG, which are rather expensive. Therefore, it is attractive to develop a seed-free solid-state crystal growth (SFSSCG) method to grown high-performance KNN single crystals. (K0.45Na0.55)0.96Li0.04NbO3 (KNL4N) single crystals were grown using SFSSCG method. The square shape and layer-like morphology of the single crystals suggest a two-dimensional (2D) nucleation crystal growth mechanism. The crystals thus obtained exhibit a giant piezoelectric coefficient d33 of 689 pC/N, which is the highest value among all the lead-free piezoelectric materials to the best of our knowledge. Moreover, the effective piezoelectric coefficient (= Smax/Emax), obtained from the maximum strain Smax induced under a high field (Emax = 30 kV/cm) unipolar electric field, can reach 967 pm/V. The giant piezoelectric response and the high Curie temperature (TC) of 432 ¡ãC indicate that SFSSCG is an effective method to prepare high-performance lead-free piezoelectric materials.|
|Yongxiang Li, Professor
Shanghai Institute of Ceramics, Chinese Academy of Sciences