Effects of Mn-doping on the piezoelectric and ferroelectric properties of (Na0.8K0.2)0.5Bi0.5TiO3 ceramics

Lead-free piezoelectric ceramics of (Na0.8K0.2)(0.5)Bi0.5TiO3+x Wt.% Mn (abbreviated as NBKT-x% Mn, x=0 similar to 0.5) were synthesized by solid-state reaction. The grain growth of the ceramics was restrained by Mn-doping at a certain extent. The mechanical quality factor Q(m) increases and the dielectric loss tan delta decreases with the increase of Mn-doping. Best piezoelectric properties were obtained for the composition of NKBT-0.2%Mn: d(33)=158 pC.N-1, tan delta=2.9% at 1 kHz, Q(m)= 110 and k(p)=30%. The P-E loops show that remnant polarization P, and coercive field E, decrease slightly with the amount of the Mn2+ increasing up to 0.2wt.% and then increase as the content of Mn2+ increases further. NKBT-0.5wt. % Mn exhibits strong ferroelectricity with remnant polarization P-r = 38 mu C/cm(2).