Effect of Polyvinylpyrrolidone Molecular Weight on the Critical Thickness, Crystallization, Densification and Properties
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0928-GG14-19
Effect of Polyvinylpyrrolidone Molecular Weight on the Critical Thickness, Crystallization, Densification and Properties of PLZT Films Z.H. Du1, and J. Ma2 1 School of Materials science and engineering, Nanyang Technological Univerisity, Ceramics lab,N4.1-B3-03,Nanyang Avenue, singapore, singapore, 639798, Singapore 2 School of Materials science and engineering, Nanyang Technological Univerisity, Ceramics lab,N4.1-B3-03,Nanyang Avenue, Singapore, Singapore, 639798, Singapore
ABSTRACT PLZT 9.5/65/35 ceramic films were prepared from the sol-gel solutions containing the stress-relaxing agent of polyvinylpyrrolidone(PVP) with the molecular weight of 40000, 360000 and 630000 (abbreviated as PVP40, PVP360 and PVP630) respectively. It is found that PVP40 can increase the critical thickness of the PLZT films to 0.22µm(compared with the critical thickness of 0.077µm in case of without PVP) and PVP360 and PVP630 can increase the critical thickness up to 0.49µm and 0.93µm individually. With the molecular weight of PVP increasing, the perovskite formation in the PLZT films was improved but the morphology of the films tended to be nano-porous. The films modified by PVP360 can be densified by optimizing the heat treatment conditions. When pyrolyzed at 600°C and then annealed at 700°C, the one-coating films with the thickness of 0.5µm were dense and exhibited a very slim hysteresis loop with the remnant polarization of 5.96x10-4µC/cm2 and coercive field of 21.51kV/cm, and a transmittance of around 90% and above in the wavelength of 450nm~900nm. KEYWORDS: polyvinylpyrrolidone, PLZT, critical thickness, crystallization, densification INTRODUCTION Pb0.905La0.095(Zr0.65,Ti0.35)0.976O3 (abbreviated as PLZT(9.5/65/35)) ceramic films above 1µm thick are very promising materials to be applied in advanced electro-optical (EO) and waveguide-based devices1,2,3. Among various film deposition techniques, sol-gel processing is an attractive method due to its flexibility in composition controlling and cost-effectivity. However, crack formation in the gel films during heat treatment is one of the major challenges for sol-gel processing of such thick films. The critical thickness i.e. the maximum thickness achieved without crack formation by one coating is often 99.5%, Aldrich Chemicals Company), zirconium propoxide(70% solution in 1-propanol, Aldrich), titanium isopropoxide(97%, Aldrich), lanthanum nitrate(Merck KGaA, Germany) and three kinds of PVP(with average molecular weight of 40000, 360000, and 630000 respectively, Fluka Chemie GmbH, Gernamy) were chose as starting materials. The molar composition of the starting solution was PbCH3COO)2/Zr(n-OC3H7)4/Ti(iOC3H7)4 /La(NO3)3/PVP/AcAcH/CH3OC2H4OH=1.01/0.6345/0.3417/0.09/1.5/0.5/30, where the mole ratio of PVP was defined according to its monomer. The solution was prepared using 10% excess PbO for compensating lead loss in the following heat treatment. First, zirconium propoxide and titanium isopropoxide were dropped into a solution of acetylacetone(>99%, Merck KGaA, Germany) and 2
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