| Piezoelectric materials, which are characterized by piezoelectric effect, can generate electricity when applied with mechanical stress and distort when applied with electric field. As being a convertor of electric energy and mechanical energy, piezoelectric materials are widely used as sensors, actuators and transducers.Lead oxide based ferroelectrics, represented by lead zirconate titanate (Pb(Zr,Ti)O3 abbreviated as PZT) dominate the area of sensor and transducer technology over half a century because of their excellent piezoelectric properties. As with the rising limitation of toxic lead and need of non-Pb materials, lot’s of work has focused on developing non-Pb piezoelectric materials. Traditionally, enhancement of the electromechanical response in piezoelectric materials is achieved by compositional engineering. Many families of lead free ceramic materials have been reported, especially the (K,Na)NbO3 based pseudoternary system and the BaTiO3 based pserdobinary system exhibit the most promising piezoelectric properties.(1-x)Ba(Ti0.94Ce0.o6)O3-x(Ba0.7Ca0.3)TiO3 (short as BTC-xBCT) system are developed and studied in our research. Our key motivation is to investigate the dielectric, ferroelectric, piezoelectric properties which are closely related to phase transition, and the electrocaloric effect of BTC-40BCT.Fist, with the value of x from 0 to 10, eleven ceramics of different compositions were fabricated by convertional solid solution method, and the sintering temperature is around 1420℃. X-ray diffraction (XRD) pattern demonstrated that all the ceramic samples are typical perovskite structure.The results of all kinds of tests indicated that there was a phase transition from Rhombohedral phase to Tetragonal phase in this BTC-xBCT system. In particular, the composition BTC-40BCT is the morphotropic phase boundary (MPB) from rhombohedral phase to tetragonal phase which start from a triple point of paraelectric cubic phase (C), ferroelectric rhombohedral (R), and tetragonal phase (T) at room temperature. At this composition, the x-ray diffraction peak around 20=45 shows a very obvious transition, and the ceramic shows the best dielectric, ferroelectric, piezoelectric properties, with d33=160 pC/N and maximum piezoelectric field strain 0.13%(d*33=430 pC/N). This kind of MPB between R and T has a much lower energy barriers for polarization rotation rather than the MPB between O (Orthorhombic) and T, as a result, the ceramics have the more excellent electric properties.Then, the electricaloric effect of BTC-40BCT was investigated. By testing the hysteresis loops from room temperature to 140℃, the temperature dependence of polarization can be analyzed out. DSC was tested, and can be used to calculate the heat capacity. At last, the Δ T in the heat insulation and depolarization was calculated. The Δ T maximum value of BTC-40BCT ceramic was 0.836 K. |
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