Direct synthesis of barium zirconate titanate (BZT) nanoparticles at room temperature and sintering of their ceramics at low temperature
Introduction
Barium titanate (BT) based materials are very important for the modern industry of electrical and electronic devices. They have ferroelectric, thermoelectric, and piezoelectric properties when they assume the tetragonal structure [1], and can be widely used in capacitors, positive temperature coefficient resistor, dynamic random access memories(DRAM), electromechanics, and nonlinear optics [2], [3], [4]. Barium zircornate titanate (BaZryTi1−yO3, BZT) is an important species of this family with potential applications such as piezoelectric transducers, DRAM, tunable microwave devices, and electrical energy storage units [5], [6], [7], [8]. With the increase of zirconium content of BZT materials, the three transition points and the three corresponding εr maxima move closer together and, finally, coalesce into a single broad maximum at y=0.10 [9]. After moving the broad maximum near room temperature, a high dielectric constant can be obtained, and thus, BZT with the composition can be generally be adopted in Y5V multilayer ceramic capacitors (MLCC) [10], [11]. When fabricated under a suitable process, the ceramics can have high dielectric constant over 104, while keeping a high breakdown voltage value which is suitable for high voltage applications [12]. BZT materials are often sintered into dense ceramics at a high temperature over 1300 °C. After adding sintering aids such as ZnO–Li2O, the sintering temperature can be lowered to around 1250 °C [10]. It is hard to obtain a dense BZT ceramics sintering at low temperature below 960 °C ( silver's melting point), but is very useful technically for multiple layer ceramic capacitors (MLCC) with magnetism-free device. Fortunately, the grain size of the ceramic powders decreases, and the sintering temperature decreases theoretically, especially for nanoparticles. Here, we report a direct synthesis route to BZT (for example BaZr0.1Ti0.9O3 in this study) nanoparticles at room temperature, which is similar to that of BT nanoparticles [13]. Their sintering characteristics at low temperature are also studied.
Section snippets
Experimental procedure
The method is evolved from direct synthesis from solution (DSS) [14] and is carried out in an enclosed system. The analytical reagents barium octahydrate (Ba(OH)2·8H2O), zirconium nitrate pentahydrate (Zr(NO3)4·5H2O) and tetrabutyl titanate (Ti(OC4H9)4) are adopted as starting raw materials to prepare the BZT nanoparticles. The titanium and zirconium (ZT) solution is obtained by dissolving 30.6 g Ti(OC4H9)4 and 4.3 g Zr(NO3)4·5H2O into 50 ml ethanol absolute. The alkali slurry is prepared by ball
Results and discussions
BZT nanoparticles can be prepared by the DSS method using isopropoxides as raw materials in isopropanol–water system [15] at 70 °C. Due to the high price and instability of isopropoxides in damp air, here we replace zirconium isopropoxdie with Zr(NO3)4·5H2O as starting raw materials. Without introducing any contamination and with low energy consumption, the synthesis process is green, environmental-friendly, convenient and efficient. In order to check the sintering characteristics, the dry
Conclusions
Similar to BaTiO3, perfect perovskite BZT nanoparticles can also be directly synthesized at room temperature. The whole process is easy to operate without any pollution to the environment. Nanoparticles with the grain size of ~10 nm can be obtained using ethanol absolute as assistant agent. The graingrowth of the nanoparticles was observed even at a temperature as low as 300–500 °C, and increased rapidly at a temperature over 600 °C, although the dense ceramics can hardly be obtained at the
Acknowledgment
The work was supported by the Hong Kong Innovation and Technology Fund (ITP 004/009NP) and PolyU internal Grant G-U846.
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