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Microstructure and electrical properties of CuO-doped K0.5Na0.5NbO3-based single crystals with low dielectric loss

CuO-doped K0.5Na0.5NbO3 (KNN)-based lead-free piezoelectric single crystals were realized by using a seed-free solid-state crystal growth (SFSSCG) method. The effect of the CuO addition on the single-crystal growth, microstructure and electrical properties of the systems was studied systemically. The addition of CuO is beneficial for the growth of the KNN-based crystals and decreases the width of ferroelectric domains of the crystals. In particular, the CuO doping significantly reduces the dielectric loss of the crystals. The lowest dielectric loss tanδ of 1% was achieved for the CuO-doped crystals with high piezoelectric constant and Curie temperature. The study on the leakage behavior of the crystals shows that the main electrical conduction mechanism is the space-charge-limited-current (SCLC). A coexisting crystalline structure with orthorhombic and tetragonal phases forms in the (1 − x)[KNN-LiBiO3]-xCuO crystals at x = 0.007–0.009. The growth kinetics and mechanism of the crystals were also investigated.