Abstract
(Na0.5Bi0.5)TiO3 (NBT) powders that have well-dispersed, uniform particle size and well-developed spherical shape were successfully prepared by a two-step hydrothermal synthesis method. Nanosized TiO2 powders were firstly synthesized by a hydrothermal method, and then the TiO2 particles are used as a raw material to synthesize NBT powders. It was found that by using the TiO2 nanoparticles as Ti source, the well-dispersed spherical NBT powders with about 200 nm in size could be obtained at 200°C for 4 h with a low mineralizer concentration of 6 mol/L NaOH in the second step. The formation of spherical NBT powders can be explained by first generating nuclei on the surface of TiO2 nanoparticles via in situ crystallization mechanism and then crystal growing and agglomerating by dissolution-recrystallization mechanism.
Highlights
Piezoelectric ceramics have been widely used in electrical devices such as actuators, accelerators, ultrasonic generators, piezoelectric transducers, filters, and sensors [1,2,3]
Spherical NBT powders are successfully synthesized by a simple two-step hydrothermal method
It was found that the hydrothermal conditions such as the mineralizer NaOH concentration, hydrothermal treatment temperature, and time have significant influences on the structure and morphology of the synthesized NBT powders
Summary
Piezoelectric ceramics have been widely used in electrical devices such as actuators, accelerators, ultrasonic generators, piezoelectric transducers, filters, and sensors [1,2,3]. Compared with the conventional solid-state reaction method, there are many wet chemical methods for the synthesis nanosized NBT powders, such as the sol-gel method, coprecipitation method, and hydrothermal method [22,23,24,25,26] Among these methods, the hydrothermal method is considered to be remarkably advantageous in the preparation of fine crystalline powders with a high purity due to the direct precipitation of crystals from solutions, controllable rate, and homogeneity of nucleation and growth of crystals. Hydrothermal reaction is usually performed under a moderate condition and does not require expensive precursors or equipments It offers a low-temperature (below 300°C) direct route to obtain ceramic powders with a fine size and uniform morphology, which can prevent undesirable changes in stoichiometry when compounds contain volatile elements such as Bi and alkali metals in many lead-free piezoelectrics. The above results clearly indicate that the size and shape of NBT powders are strong correlation with synthesis conditions, especially the NaOH concentration. The crystal growth mechanism in the hydrothermal reaction process is discussed
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