Study On Composite Modification Of High Temperature Aurivillius Phase Sodium Bismuth Titanate Piezoelectric Ceramics

The Aurivillius-type bismuth layer-structured ferroelectric(BLSF) ceramics was first studied by Aurivillius. Bismuth layer-structured ferroelectrics (BLSFs) ceramics are potential candidate lead-free materials in piezoelectric device application, especially for high temperatures and high frequencies application. This is because of their relatively low dielectric constants, low aging rate, low dielectric dissipation factors, high dielectric breakdown strengths, stronger anisotropic electromechanical coupling factors and low temperature coefficients of resonant frequency. These features, together with their high Curie temperature (Tc), make BLSFs attractive in high temperature and high frequency resonance applications.1. The formula of the ceramics is Na0.5Bi4.5(1+x)Ti4O15(x=-0.04,0.00,0.04,0.06). Na0.5Bi4.5Ti4O15-based materials with change the Bi content were synthesized using conventional solid-state processing. To change the Bi content significantly enhancedthe piezoelectric activity of NBT piezoelectric ceramics. The piezoelectric coefficient d33 of the x=0.04 Bi-doped NBT was found to be 16-pC/N.Therefore, planar electromechanical coupling coefficient kp=7%, thickness electromechanical coupling coefficient kt=28%, exhibiting a strong anisotropic behavior. The Curie temperature increased slightly with increasing Bi modification, where the tanδ of x=0.04 was found to be only 0.30%. The resistivity of the sample is still higher than 104Ω·m even at 500℃. Na0.5Bi4.5Ti4O15-based ceramics are promising candidate for high temperature applications.2.The Na0.5Bi4.5Ti4O15-based materials with B-site co-modification (W/Nb) were synthesized using conventional solid-state processing in first. The formula of the ceramics is Na0.5Bi4.5Ti4-x(W/Nb)x/2O15(x=0.000,0.015,0.020,0.025,0.040). The (W/Nb) modification of Na0.5Bi4.5Ti4O15-based materials resulted in the obvious improvement of the piezoelectric activity and dielectric permittivity. The dielectric and piezoelectric properties of Na0.5Bi4.5Ti4O15-based ceramics exhibiting a very stable temperature behavior, together with its high Tc-645℃, excellent piezoelectric coefficient-28pC/N, the extremely high value obtained through a B-site(W/Nb) modification in first and very low temperature coefficient of resonant frequency, making the W/Nb co-doped Na0.5Bi4.5Ti4O15-based ceramics a promising candidate for high temperature applications.3. A series of (NaBi)0.5Bi4Ti3.98(WNb)0.01O15 piezoelectric ceramics with Ce modification were prepared. The influence of Ce on dielectric and piezoelectric properties was investigated. The formula of the ceramics is (NaBi)0.5Bi4-xCexTi3.98(WNb)0.01O15(x=0.00,0.02,0.04,0.06). It was found the piezoelectric activities of (NaBi)0.5Bi4Ti3.98(WNb)0.01O15 ceramics were significantly improved by cerium modification. The piezoelectric coefficient d33 and Curie temperature Tc of the x=0.04 cerium-modified (NaBi)0.5Bi4-xCexTi3.98(WNb)0.01O15 were found to be 31pC/N and 660℃, respectively.The planar electromechanical coupling coefficient kp was 8%, the thickness electromechanical coupling coefficient kt was 36%, the dielectric loss has a value of 0.20% at room temperature. The resistivity of x=0.04 sample is higher than that of x=0.00 sample in the temperature range from 350℃ to 560℃ and the resistivity of the sample is still higher than 105Ω·m even at 500℃.