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C8.16.1

Dielectric and Ferroelectric Properties of Modified BiFeO3-PbTiO3 Thin Films Derived from Sol-gel Processing JinRong Cheng1,2 and L.Eric Cross1 1 Materials Research Institute, The Pennsylvania State University University Park, PA 16802 2 School of Materials Science and Engineering, Shanghai University Shanghai 201800, P.R.China ABSTRACT In this paper, thin films of La- modified (Bi,La)FeO3-PbTiO3 (BLF-PT) morphotropic phase boundary (MPB) solid solutions have been prepared by using sol-gel processing. A thin Pb(Zr,Ti)O3 (PZT) template layer was introduced to make BLF-PT thin films adhere tightly to the platinized silicon (Pt/Ti/SiO2/Si) substrate. X-ray diffraction (XRD) analysis revealed that BLF-PT thin films were of the perovskite structure without detectable pyrochlore phase annealing at 650-750oC. The cross sectional and plain view images of or our specimen were observed by using the scan electrical microscope (SEM). The room temperature dielectric constant K and tanδ were of ~800 and 4% respectively, for BLF-PT thin films using a measurement frequency of 1 kHz. Our preliminary experiments indicated that the sol-gel derived BLF-PT thin films have good insulation resistance and measurable dielectric and ferroelectric responses. INTRODUCTION BiFeO3 based thin films have received recent interests due to the unique properties relative to their bulk forms.[1,2] The epitaxial BiFeO3 thin films have been currently deposited on the single crystal (100) SrTiO3 substrate by using the pulsed laser deposition ( PLD) techniques. No conductivity problem was observed for BiFeO3 thin films. A giant spontaneous polarizations Ps of ~60 µC/cm2 have been achieved, which is 10 times greater than that of BiFeO3 single crystal. However, the coercive field of the films is as high as 200 kV/cm. In addition to pure BiFeO3 perovskite thin films, bismuth contained solid solutions have also been developed in the thin film form.[3] For example, epitaxial 1 µm thick BiScO3-PbTiO3 thin films on (100) LaAlO3 single crystal substrate exhibited good ferroelectric and piezoelectric properties, which was similar to their excellent performances of the bulk ceramics at the same compositions. Thin films of bismuth-contained materials were attracted due to their potentials for higher Curie temperature materials and stronger polarizations caused by Bi3+ cation. Most recently, we first made excellent piezoelectric ceramics of BiFeO3-PbTiO3 (BF-PT) solid solutions by using La substituents.[4] This was our motive to prepare BLF-PT into the thin film form. In this paper, the conventional sol-gel technique was used to prepare the lanthanum modified BF-PT thin films on the widely used platinized silicon substrate. As mentioned above, pure BiFeO3 has a large value of Ec. Our objective was to decrease Ec by making BiFeO3 thin film solid solutions with PbTiO3. We succeeded in dissolving multiple components into a stable solution. A template layer of PZT was introduced to improve the sintering property. The crystallized BLT-PT thin films were determined