Microstructure,Electrical Properties of Mn-doped Sr_(2-x)Ca_xNaNb_5O_(15)(x=0.05～0.35) Lead Free Ceramics

Lead-free piezoelectric ceramics Sr2-xCaxNaNb5O15+ywt%MnO2(x=0.05-0.35,y=0,0.3,0.5)(SCNN-M) were fabricated by conventional solid-state processes,and their microstructure,phase transformation,dielectric,piezoelectric and ferroelectric properties were investigated systematically.Our results reveal that Ca2+ ions have entered into the Sr2NaNb5O15 lattices to form a solid solution and the doping of MnO2 is effective in promoting the densification of the ceramics.With the MnO2 doping,all the ceramics can be well sintered at a relative low tem-perature and exhibit a dense and pure tungsten-bronze structure.The addition of Ca2+ has no remarkable effect on the microstructure and MnO2 caused a significant promoted grain growth.Compared with the pure SCNN ceramics,the dielectric and piezoelectric properties of SCNN-M ceramics were greatly enhanced.At room temperature,the SCNN-M ceramics with x=0.5 and y=0.5 exhibits the optimum properties:piezoelectric coefficient d33=190pC/N,mechanical quality factor Qm=1455,planer electromechanical coupling factors Kp=13.4%,thickness electrome-chanical coupling factors Kt=36.5%,dielectric constant er=2123,loss tangent tanδ=0.038,remanent polarization Pr=4.76μC/cm2,spontaneous polarization Ps=9.36μC/cm2,coercive field Ec=12.68kV/cm,and curie temperature Tc=260℃.Therefore,the SCNN-M ceramics are a good candidate material for lead-free piezoelectric ceramics.