Dielectric and Pyroelectric Properties of Lead-Free Sodium Bismuth Titanate Thin Films Due to Excess Sodium and Bismuth Addition
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Pb-free ferroelectric (Na0.5Bi0.5)TiO3 (NBT) thin films were prepared by a modified sol-gel process. Theirstructural, dielectric and pyroelectric properties were investigated as a function of the excess Na/Bi ratio and the annealingtemperature. In the case of thin films containing no excess Na and Bi, only partial amounts of the perovskite NBT werecrystallized, where the films consisted mainly of the pyrochlore phase of Bi2Ti2O7 for annealing conditions of 600~800oC. With increasing excess Na/Bi ratio, the proportion of the perovskite phase effectively increased due to the compensationof the volatile Na and Bi components. For a Na/Bi ratio of 2.0, the thin film with single NBT perovskite phase wasobtained within XRD detection limit after annealing at 700oC for 10 min and it showed the excellent dielectric properties,εr of ~550 and tan δ of 0.03. While these properties were degraded for Na/Bi ratio of 2.5 despite the existence of pureperovskite phase. The NBT thin film with Na/Bi ratio of 2.0 are also promising candidates for applications requiringpyroelectric devices because it was found to have pyroelectric coefficients of 1.3~7 nC/cm2K in the temperature rangeof 30~100oC.
Abstract
Pb-free ferroelectric (Na0.5Bi0.5)TiO3 (NBT) thin films were prepared by a modified sol-gel process. Theirstructural, dielectric and pyroelectric properties were investigated as a function of the excess Na/Bi ratio and the annealingtemperature. In the case of thin films containing no excess Na and Bi, only partial amounts of the perovskite NBT werecrystallized, where the films consisted mainly of the pyrochlore phase of Bi2Ti2O7 for annealing conditions of 600~800oC. With increasing excess Na/Bi ratio, the proportion of the perovskite phase effectively increased due to the compensationof the volatile Na and Bi components. For a Na/Bi ratio of 2.0, the thin film with single NBT perovskite phase wasobtained within XRD detection limit after annealing at 700oC for 10 min and it showed the excellent dielectric properties,εr of ~550 and tan δ of 0.03. While these properties were degraded for Na/Bi ratio of 2.5 despite the existence of pureperovskite phase. The NBT thin film with Na/Bi ratio of 2.0 are also promising candidates for applications requiringpyroelectric devices because it was found to have pyroelectric coefficients of 1.3~7 nC/cm2K in the temperature rangeof 30~100oC.
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