Study On Preparation And Properties Of K_0.5Na_0.5NbO₃ Ceramic Films

As an important environment-friendly piezoelectric ceramic,with the properties of high piezelectric constant,low dielectric constant and high Curie temperature, K0.5Na0.5NbO3 has become one of the most popular studied braches of lead-free piezoelectric ceramics. With the rapid development of the drive for miniaturization and micro electro mechanical system(MEMS),the fabrication of K0.5Na0.5NbO3 thin/thick ceramic films have been promoted for applications. In this thesis, we focus on synthesis of K0.5Na0.5NbO3 thin film by sol-gel method and fabrication of K0.5Na0.5NbO3 thick film by powder-sol processing. The preparation method and electric properties were discussed.Frist,high-active Nb(OH)5 was synthesized by the reaction between Nb2O5 and HF.The stability and transparent K0.5Na0.5NbO3 sol was prepared by polymeric precursor method with Nb(OH)5,K2CO3 and Na2CO3 as the starting materials,citric acid as chelate,ethylene glycol as esterificate.The feasible process parameter:the molar ratio of metal cations/CA=3/1 and CA/EG=1/2, PH=5-8 and temperature< 150℃.The preparing process of K0.5Na0.5NbO3 ultra-fine powder and some related issues were studied.The result revealed that single perovskite phase KNN ultra-fine powder was synthesized with the molar ratio of K/Na=1,(K+Na)/Nb=1.6,calcined at 600℃for 2h. The powder showed fine cubic grain of about 200nm.Then, K0.5Na0.5NbO3 thin film was prepared by sol-gel method.The thin film had single perovskite phase, (100) orientation, dense,crack-free and uniform grain with sol concentration of 0.3mol/L;K/Na=1,(K+Na)/Nb=1.6; spin-coating speed of 5000rmp and time of 30s;7 coatings;drying temperature of 700℃and time of 10min; annealing temperature of 700℃and time of 30min; Pt/Ti/SiO2/Si substrate.Based on the above, the fabrication of K0.5Na0.5NbO3 thick film by powder-sol processing was studied. We researched how the powder dispersed in the slurry and the influence of the powder concentration and spin-coating times on the thickness and microcosmic appearance of thick film.Also, we improved the surface roughness by thick-thin alternation spin-coating technology. We could obtained dense and crack-free thick film with thickness of 1μm～4.5μm by adjusting technics.Last, the electric properties of KNN ceramic films had been studied.The test showed:At 1KHz frequency, the dielectric constant and loss tangent of KNN thin film wereεr=100.17,tan8=0.49;At 1MHz frequency, the dielectric constant and loss tangent of KNN thin film wereεr=29.71, tan8=0.11; The remnant polarization Pr was 1.1μC/cm2.At 1KHz frequency, the dielectric constant and loss tangent of KNN thick film with thick-thin alternation spin-coating technology and powder/sol=2:1 wereεr=248.12, tanδ=0.58;At 1MHz frequency, the dielectric constant and loss tangent of KNN thick film wereεr=26.02,tan8=0.1.We could gained hysteresis loops but the remnant polarization Pr was under 1μC/cm2. The electric properties had improved compared with the thick film of thick-thick spin-coating technology.