Effects of MnO2 doping on structure, dielectric and piezoelectric properties of 0.825NaNbO3 -0.175Ba0.6 (Bi0.5 K0.5 )0.4 TiO3 lead-free ceramics

Abstract Lead‐free ceramics 0.825NaNbO 3 –0.175Ba 0.6 (Bi 0.5 K 0.5 ) 0.4 TiO 3 + x mol% MnO 2 were prepared by an ordinary sintering technique and the effects of MnO 2 doping on the structure, dielectric, and piezoelectric properties of the ceramics were studied. The ceramics with perovskite structure are transformed from tetragonal to pseudocubic phases by increasing the doping level of MnO 2 . After the addition of MnO 2 , the Curie temperature T C of the ceramics decreases and the ferroelectric–paraelectric phase transition at T C becomes more diffusive. Because of the donor and acceptor doping effects of Mn ions simultaneously, the piezoelectric constant d 33 , electromechanical coupling coefficient k p , relative permittivity ε r , and mechanical quality factor Q m are enhanced considerably after the addition of 1 mol% MnO 2 . The ceramic with 1 mol% MnO 2 doping possesses the optimum piezoelectricity ( d 33 = 131 pC/N and k p = 21.8%) and relatively high Q m = 627.