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Preparation and temperature stability of the KNLNT -based lead-free piezoelectric ceramics

Author: MaDiFei
Tutor: YangZuPei
School: Shaanxi Normal University
Course: Materials Science
Keywords: KNLNT lead-free piezoelectric ceramics Piezoelectric properties Dielectric properties Ferroelectric properties Temperature stability
CLC: TM282
Type: Master's thesis
Year: 2010
Downloads: 94
Quote: 2
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Abstract


The piezoelectric ceramic material is a high-tech international competition is extremely fierce functional materials, its development in a leading position in the entire field of Electronic Science and Technology. In order to protect the environment and ensure the sustainable development of human society, the development of high performance and good temperature stability, lead-free piezoelectric ceramic materials has become a major trend of the Materials Research. KNbO3-NaNbO3 (KNN) based lead-free piezoelectric ceramics with its high piezoelectric and ferroelectric properties of strong high Curie temperature much attention and become a hot research field of the material. KNN-based piezoelectric ceramic is considered to be the most promising new lead-free piezoelectric ceramic system to replace the lead-based piezoelectric ceramics, however, prepared by conventional ceramic process is difficult due to the KNN ceramic piezoelectric properties on the preparation conditions with a strong sensitivity compact structure and stable performance KNN ceramic. This article Select (K0.46Na0.50Li0.04) (Nb0.85Ta0.15) O3 (KNLNT) ceramics as a base system, milling, burn, sintering, polarization process conditions, and then to KNLNT ceramic Add new group CaTiO3, to expect to improve the temperature stability of the ceramic in the premise to maintain its higher electrical performance. The main contents are as follows: (1) study the milling of time on KNLNT ceramic phase structure, microstructure, piezoelectric properties, dielectric properties and ferroelectric properties. The results show that: the milling time range of 5-25 h, the resulting calcined powders are to achieve sub-micron level, calcined powders and ceramic samples are pure perovskite structure. As the milling time increases, the degree of uniformity of the ceramic grains are enhanced when the milling time is 20 h, preferably ceramic grains were uniform in size, the apparent density of the sample reaches a maximum. Ferroelectric hysteresis loops of ceramic samples are relatively saturated, its optimized milling time of 20 h, the resulting ceramic has the best electrical properties, electrical properties, respectively: (d33) = 248 pC / N, Kp = 0.50 , Qm = 70, εr = 1130, tanδ = 0.019, Ec = 14.31 kV / cm, Pr = 28.38μC/cm2. (2) study the calcining temperature, calcining time, sintering temperature and polarization process (polarization voltage, polarization and polarization temperature) the conditions on KNLNT ceramic of the phase structure, microstructure, piezoelectric properties, dielectric electrical properties and ferroelectric properties. The results show that: burn-temperature range of 750-950 ℃, KNLNT ceramics are pure tetragonal perovskite structure, with the calcining temperature rise, ceramics d33, Kp, εr and Pr first increase and then decrease small, Qm and tanδ first decrease and then increase, the Ec little change. Ceramic optimum calcining temperature of 850 ° C, the ceramic grains full, the apparent density of the ceramic to achieve maximum piezoelectric, dielectric, ferroelectric properties. Different burn-in time, the ceramic samples were pure tetragonal perovskite phase structure, with increasing burn time, ceramic d33, Kp and εr first increases and then decreases, Qm and tanδ first reduced to increase . Its optimum burn time of 10 h, in this case, the ceramic grains are more full, growth is relatively uniform, and the apparent density of the ceramic, the best electrical performance. When the burn-in time for 9h, the test temperature range of 25-50 ℃ ceramic Pr and Ec gradually with increasing test temperature increases. Different sintering temperature ceramic samples are pure perovskite structure with the sintering temperature ceramics (d33), Kp and εr first increases and then decreases, Qm and tanδ first reduced increase. When the sintering temperature of 1135 ℃, full ceramic grain, uniform growth, apparent density maximum, piezoelectric, dielectric and ferroelectric properties. The polarization voltage, polarization time and polarization temperature piezoelectric properties of ceramic samples of KNLNT greater impact, the optimum polarization: polarization voltage of 3.5 kV, dwell time 15min, a poling temperature 80 ° C. Under this condition, the obtained ceramic various performance parameters, respectively: ρ = 4.35 g/cm3, d33 = 262 pC / N, Kp = 0.54, Qm = 74, εr = 1130, tanδ = 0.019, Pr = 28.38μC / cm2, Ec = 14.31 kV / cm. (3) to study under the best conditions for the preparation of a the new component CaTiO3 the addition of KNLNT ceramic phase structure, microstructure and piezoelectric properties, dielectric properties, ferroelectric performance and temperature stability. The results show that: the different components of the ceramic samples are pure perovskite structure, with the CaTiO3 content increases, the apparent density of the ceramic progressively decreases, the uniformity of the grain size reduced, ceramics d33, Kp and Qm both showed reduced gradually, εr first decrease and then increase, tanδ is gradually increased. The CaTiO3 adding samples orthogonal tetragonal phase transition temperature from the room temperature, improving the temperature stability of the samples. Considering the electrical properties at room temperature and temperature stability of the ceramic samples, 0.992KNLNT-0.008CT ceramic best performance, their electrical properties were: D33 = 232pC / N, Kp = 0.43, Qm = 62, εr = 1062, tan δ = 0.024. Through the research, we get a better ceramic components: 0.992 (K0.46Na0.50Li0.04) (Nb0.85Ta0.15) O3-0.008CaTiO3, better temperature stability and the electrical properties with greater potential practical value.

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