Sodium bismuth titanate based lead-free piezoelectric ceramics
Sodium bismuth titanate (Bi1 / 2Na1 / 2TiO3), referred to as the BNT, is considered a possible lead-based piezoelectric ceramics to replace lead-free piezoelectric ceramic system, it is A bit complex ions such as calcium titanium invented by Smolensky mine ferroelectrics, ferroelectric strong, good piezoelectric properties, low dielectric constant and good acoustic properties and other excellent features, and low sintering temperature, which is being widely studied.
Excellent performance BNT-based lead-free piezoelectric ceramics is determined by its special chemical composition and microstructure to achieve, and the powder morphology, chemical composition uniformity, etc., directly affect the composition and structure of ceramic materials as well as its electrical properties. Only synthetic ceramic powder of high purity, fine particles, evenly distributed, the exact stoichiometry, be possible to achieve low-temperature sintering, thereby improving the density and properties of piezoelectric ceramics products.
The traditional preparation of lead-free piezoelectric ceramics were prepared by solid state reaction powder, mixing technical problem with this approach, uniformity and other aspects of the existence of a direct impact on the performance of the final ceramic product. With the rise of technology and other soft solution process for the preparation of fine electronic ceramics in preparation, the use of these technologies BNT ceramic powder synthesis has drawn increasing attention.
Preparation Method one: solid state reaction method
Solid state reaction method is the traditional method for preparing functional ceramics. The basic principle of this method is that the desired oxides, carbonates or nitrates of elements mixed by grinding, after calcining the decomposition of these salts, is reacted with a solid phase, the chemical composition of the ceramic and to generate a desired crystal phase powder.
Currently, the preparation of BNT-based ceramic powders were powered by solid state reaction method. T.Takenaka and others to bismuth oxide, sodium carbonate, titanium dioxide and barium carbonate as raw materials, systematic study prepared by solid state reaction of (Bi1 / 2Na1 / 2) 1-xBaxTiO3 (abbreviated as BNBTx) ceramic dielectric electric, piezoelectric and ferroelectric properties. According to experimental results, when in the vicinity of 0.06 x exists BNBTx tripartite system - the same type of quasi-tetragonal phase boundary, then the electrical properties of ceramics are shown in Table BTBT6.
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Since the solid-phase method with low cost, high yield, and the preparation process is relatively simple, etc., is the synthesis of functional ceramic powder at home and abroad the most common method. However, prepared by solid state reaction powder tend to have coarse, less active, less chemical uniformity, easy reunion inadequate, making it difficult to obtain higher performance ceramics.
Preparation Method Two: sol - gel method
For the shortcomings of the solid-phase method and the development of high-performance electronic ceramics BNT-based, US-led study conducted in developed countries take the lead in the preparation of BNT base wet chemical powder, sol - gel method is one of the preparation of the ceramic oxide powder effective method body, which is used in the preparation of perovskite-type nano-powders in many places.
a) the sol - gel method, the precursor is dissolved in a solvent (water or organic solvent) to form a homogeneous solution, hydrolysis or alcoholysis to produce a sol by reaction with the solute and the solvent in the pre-treated powder was suspended inclusions mixed with liquid, under the action of sol gel into a gel by aging, then get after calcination methods coated composite powders. Using this method, the various components may be implemented atom or materials are uniformly mixed at the molecular level and thus can be obtained a highly uniform dense material, the piezoelectric properties of the ceramic will be greatly improved.
Shandong University 赵明磊 such as bismuth nitrate, sodium acetate, butyl carbonate and barium hydroxide as raw materials four to glacial acetic acid as the solvent, ethylene glycol ether as stabilizer, with the amount of water to obtain a uniform gel hydrolysis pretreatment to remove byproducts and solvents, 600 degree heat was crystallized BNTx powder. With this system, the powder obtained has a larger ceramic BNBT6 remanent polarization (Pr = 25uC / cm ^ 2) and a smaller coercive field (Ec = 28kV / cm), piezoelectric constant d33 = 173pC / N, was prepared by the traditional process than with the composition of samples.
