Of Sbn Ceramic Preparation And Performance Of Research

As every country in the world pays more and more attention to environmental protection, the research of lead-free piezoelectric ceramics becomes very important. Compared with traditional lead-based piezoelectric ceramics, there are many drawbacks of lead-free piezoelectric ceramics. So, it is practical and realistcic to find a lead-free piezoelectric system with optimum properties. Due to the properties of SrxBa1-xNb2O6 (abbreviated to SBN), such as pyroelectric and linear electro-optic coefficients. SBN is considered to be one of the most promising lead-free ceramics to substitute lead based ceramics.We adopted conventional oxide-mixed method to prepare SBN-based lead-free piezoelectric ceramics. The effects of composition, sintering technique and doping element were also investigated. The major content was as follows:Firstly, the effects of Sr/Ba ratio and sintering technique on phase structure, microstructure and electrical properties were studied detailedly. The results showed that all samples exhibited single tungsten bronze (TB) structure. Prepared powder calcined at 1200℃/4h, when x<0.51, it exhibited single-phase tungsten bronze structure, and when x> 0.51, XRD patterns emerged SrNb2O6 peak, that is, as Sr/Ba increases, the powder calcined become difficult. When calcined at 1250℃for 4h, all samples exhibited single-phase of tetragonal tungsten bronze structure, that is, the prepread powder for the same components, increase calcined temperature, easy to obtain single-phase. The ceramics sintered at 1380℃with relatively compact and homogenous microstructure without abnormal grain growth can be obtained at x=0.53. Dielectric constant increased and Tc decreased from 86℃to 65℃with increasing the Sr/Ba ratio, and at the same time the ceramics presented better properties, which were as follows:SBN53 has the clear grain boundary and uniform grain size, its density reaches the highest value of 4.934 (92% of theoretical density). Tc=77℃,εm=2774, Pr= 1.09μC/cm2, Ec=3.66 kV/cm。The material belongs to an ideal relaxor ferroelectric.In order to decrease dielectric loss of the ceramics and improve the electrical properties, further, we choose Na+and Ta5+ as dopants. Only Na+ as dopant, all ceramics exhibited single tungsten bronze (TB) structure as Na+ content ranged from 0.1 to 0.8 mol. The SEM images indicated that with Na+ content increasing, the average grain size increased, and the compact and uniform ceramics can be obtained at Na+= 0.6 mol. With Na+ increasing, relaxor behavior disappeared, temperature frequency stability increased and the Curie temperature Tc increases from 77℃to 310℃. When Na+= 0.6 mol, the electrical properties of the ceramics sintered at 1380℃were better, which were as follows:Tc=310℃,εm=2021, Pr= 2.07μC/cm2,Ec=6.46 kV/cm. Only Ta5+ as dopant. As Ta content range from 0.05 to 0.40, all samples exhibited single tungsten bronze (TB) structure, all the diffraction peaks of Sr0.53Ba0.47Nb2-xTaxO6 slowly shift to the left. With Ta5+ increasing, the average grain size decreased, and the compact and uniform ceramics can be obtained at Ta5+=0.2mol. Tc decrease from 75℃to-57℃as Ta5+ increase from 0.05 to 0.4, while the maximum dielectric constant reduced from 2723 small to 1294. When Ta5+=0.1 mol, the electrical properties of the ceramics sintered at 1430℃were better, which were as follows:Tc=25℃,εm=2387, Pr=0.24μC/cm2,Ec=1.76kV/cm.Na+, Ta5+ doped together, Ta5+ content is 0.1mol, when Na+content in the range of 0.3 to 1.05, all samples exhibited single tetragonal tungsten bronze structure. When the content of Na+>0.7, the sample exhibit a peak of phase transition at 130℃. With Na+ increasing, the temperature frequency stability increased, but relaxor behavior disappeared. When Ta5+=0.1mol and Na+= 0.6mol, the electrical properties of the ceramics sintered at 1400℃were better, which were as follows:Tc=248℃,εm=2472, Pr=2.07μC/cm2,Ec=7.25 kV/cm.Although doped Ta5+ can increase the density of the ceramic decrease dielectric loss, Na+doped can increase the Tc. But the sintering temperature of SBN ceramics is too high. So finally we choosed LiSbO3 as dopant. We studied the effects of LiSbO3 content on phase structure, microstructure and electrical properties in order to improve the dielectric properties of the ceramics and decrease the sintering temperature. The results show that:The X-ray diffraction patterns indicated that all samples exhibited single tungsten bronze (TB) structure as LiSbO3 content ranged from 0.01 to 0.04. The addition of LiSbO3 promote densification of ceramics. The SEM micrographs showed that with LiSbO3 content increasing, the average grain size decreased and the relatively compact and uniform ceramics can be obtained at x=0.03. The addition of LiSbO3can decrease the sinter temperature from 1380℃to 1280℃. The temperature dependence of dielectric constant and dielectric loss revealed that all ceramics were relaxor ferroelectrics. When LiSbO3=0.02 mol, the electrical properties of the ceramics sintered at 1280℃were better, which were as follows:Tc=44℃,Pr=0.59μC/cm2,Ec=2.36 kV/cm.