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Preparation and properties of sodium bismuth titanate based lead-free piezoelectric ceramics

Author: ZhaoYa
Tutor: LiQuanLu
School: Shaanxi Normal University
Course: Condensed Matter Physics
Keywords: Sodium bismuth titanate Solid state reaction method Replace Dielectric properties Piezoelectric properties
CLC: TM282
Type: Master's thesis
Year: 2011
Downloads: 100
Quote: 1
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Abstract

Substituted sodium bismuth titanate Bi0.5Na0.5TiO3 (BNT) based piezoelectric ceramics as an A-bit ionic complex perovskite type ferroelectric currently being studied extensively, and is considered to be the most promising lead-free material system one. In this paper, the preparation of ceramic samples of traditional solid-phase sintering method, through the use of modern testing and analysis techniques, a systematic study of the preparation process to replace the modified and the addition of a third-component factors of BNT-based ceramic material properties, phase structure, microstructure and piezoelectric and dielectric properties. First prepared by the binary system of lead-free piezoelectric ceramics (1-x) Bi0.5Na0.5TiO3-xBaTiO3 (BNT-BT) to study the phase structure of the firing process and BaTiO3 (BT) Change in Composition of the BNT-BT ceramic samples microstructure and piezoelectric, dielectric properties investigated. Through the sample morphology observed, as well as the density, phase structure and piezoelectric, dielectric properties of the test, get the best firing conditions and overall performance morphotropic phase boundary (Morphotropic Phase to Boundary, the MPB) the nearby ceramic formulations. The study showed that: (1) calcining temperature is low, easy to produce miscellaneous phase, is not conducive to the main phase synthesis, the calcining temperature is too high, hard, grinding difficult samples, resulting in back sintering activity decreased, is not conducive to the porcelain appropriate calcining temperature help reduce pores and defects, grain boundary was uniform grain size; appropriate increase in the sintering temperature, will help improve the ceramic sample density and electrical properties; For BNBT6, 850 ℃ calcining and sintering temperature of 1160 ℃ (insulation 2h) better performance of the ceramic samples. (2) X-ray diffraction (XRD) analysis shows that the large ionic radius of the barium ions Ba2 partially substituted into the lattice sodium Na and bismuth ions Bi3 occupy the A-site, and are forming a single structure of perovskite solid solution, and so that the diffraction This indicates that the unit cell volume is larger; scanning electron microscopy (SEM) images show the right amount of Ba2 instead contribute to grain refinement to improve the sintering and ceramic density; dielectric temperature spectrum curve peaks to lower angle offset Ba2 can reduce the dielectric constant of the Curie point at the peak, so that the Curie temperature is shifted toward lower temperature, increasing the dielectric to exhibit typical relaxation characteristics; With BT content increases, d33, Kp and ε33T/ε0 first increases and then decreases, while the tanδ showed a trend of decreases and then increases. Microstructure and electrical properties of ceramic two factors determine the morphotropic phase boundary range of BT content x = 0.06 ~ 0.10 (mol) of the system, rhombohedral, tetragonal phase coexist, showing the typical characteristics of relaxation and x = 0.06, the better the comprehensive performance of the ceramic samples 0.94BNT-0.06BT (BNBT6), the volume density of the ceramic 5.664g/cm3, piezoelectric constant d33 to 120PC / n, relative permittivity ε33T / ε0 600 planar electromechanical coupling factor Kp 0.202, dielectric loss tanδ of 2.1%, the mechanical quality factor Qm 205. (3) BNBT6 a relaxor ferroelectric ceramic material anisotropy and large electromechanical coupling coefficient and better prospects in the ultrasound field. With the introduction of the BT depolarization temperature Td reduced, so that the sintering temperature is narrowed, the temperature stability deteriorates, the system of application of ceramic affected. Secondly, in BNBT6 were introduced based on a lithium bismuth titanate (BLT) and bismuth potassium titanate Bi0.5K0.5TiO3 (BKT), the formulations were: (0.94-x) the BNT-0.06BT xBLT and (0.94-y) BNT The-0.06BT yBKT, BLT and BKT content ceramic phase structure, microstructure and electrical properties. Study shows that: A bit of sodium ions Na after the lithium ion Li and potassium K partially substituted, can be fully diffused into the crystal lattice to form a single structure of the perovskite-type solid solution, lithium ion Li Na small radius is smaller than the diffraction peaks to angle offset in the cell volume becomes small, and the radius of potassium K Na large, so that the diffraction peak is shifted to a lower angle, indicating that the cell volume becomes large; within the composition range studied, most of all ceramic samples The relatively dense, porosity, exhibit good sintering properties, the Li content is high, the crystal may occur abnormal grain increases, this may be provided with the introduction of a Li can significantly reduce the sintering temperature of this feature related. Li introduction of no - Quartet MPB phase boundary, always increasing trend with increasing Li content the relative permittivity ε33T/ε0 and dielectric loss tanδ, piezoelectric constant d33 and planar electromechanical coupling coefficient KP change BNBT6 tripartite trends are first increases and then decreases x 0.05, 1110 ℃ sintered samples piezoelectric constant maximum at d33, KP, ε33T/ε0, tanδ, respectively, for 128pC / N 0.22,800,2.5% . The K content hours did not change the tripartite of BNBT6 - Quartet MPB phase boundary, but y is equal to 0.09 crystal into a tetragonal phase, ε33T/ε0, tanε, d33 and Kp changes in the phase transition. The amount of BLT and BKT solid solution, is conducive to improved performance of the ceramic piezoelectric. Phase transition of the ternary system is more complex, especially BNT-BT-BKT morphotropic phase boundary is uncertain, doped ferroelectric relaxation characteristics to be studied, and need to be further improved formulation optimization process, improve data in order to obtain comprehensive performance more excellent two ternary BNT-BT-BLT and BNT-BT-BKT lead-free piezoelectric ceramics.

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