Abstract
Potassium Sodium Bismuth Titanate (KNBT) ceramics, with the general formula (1 - x)K0.5Bi0.5TiO3 -xNa0.5Bi0.5TiO3, have been synthesized following hydrothermal route, starting with solid solutions of pure perovskite nanoceramics of KBT and NBT in desired stoichiometric weight ratios, followed by sintering between 850°C and 1000°C for few hours. Pure KNBT nanoceramics with perovskite structure, having mean particle size around 30 nm, could be obtained. Morphology of the samples is found to depend strongly on composition. A change of composition results in a phase change, as evident from X-ray structure analysis. This phase change is a result of rhombohedral to tetragonal morphotropic phase boundary (MPB) in the sample with x around 0.80. Composition dependent occurrence of MPB leads to formation of needle like structures with micrometer length scales. These are typical of tetragonal lamellar structures, suggesting partial induction of tetragonal polar order from rhombohedral structure at MPB. Dielectric and piezoelectric properties, such as dielectric constant and loss, piezoelectric coefficients and figures of merit, exhibit threshold maxima in their values at the composition corresponding to MPB. These values reported for a lead-free piezoceramic, synthesized by a comparatively simple hydrothermal route, are highly promising, and comparable to well-known PZT.
Highlights
Piezoceramics such as Lead ZirconateTitanate (PZT) are the most widely used materials for piezoelectric applications due to their high performance in terms of sensitivity, reproducibility and dynamic range
In this work we report a novel method for the synthesis of solid solutions of Potassium sodium bismuth titanate (KNBT), with stoichiometric formula (1 − x)K0.5Bi0.5TiO3 − xNa0.5Bi0.5TiO3, by sintering solid solutions of Potassium Bismuth Titanate (KBT) and Sodium Bismuth Titanate (NBT) nanoceramics, synthesized following hydrothermal route at a temperature below 200 ̊C, which is much lower than needed for other methods
It is clear that the properties peak to a maximum for the composition with x = 0.80, and is assigned to be as due to this composition being close to a Morphotropic Phase Boundary (MPB) where the ions are subjected to comparatively large remnant polarization
Summary
Piezoceramics such as Lead ZirconateTitanate (PZT) are the most widely used materials for piezoelectric applications due to their high performance in terms of sensitivity, reproducibility and dynamic range. In contrast to the solid-state reaction route outlined above, hydrothermal synthesis has the potential to produce highly pure and homogeneous metal oxide powders with good control over their stoichiometry, crystallite size and morphology [16] [17]. Utilization of such well-defined metal oxide powders as precursors for piezoelectric ceramics has received much attention, because high performance ceramics close to a MPB have been obtained by texturetreatment [18] or template grain growth [19] utilizing them. It is seen that the above composition of this lead-free composite ceramic, synthesized following a relatively simple procedure, exhibits piezoelectric properties comparable to PZT type ceramics
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