Study On The Mechanical Properties And Preparation Of Nano-composite PZT

Nano-phase composite ceramic is a composite material which contains nano-phase particles in homogeneous dispersion state. Nano-phase composite ceramic can enhance its mechanical properties which mainly express in three points: fracture strength, fracture toughness and high temperature resistance. And it can enhance hardness, elastic modulus, Weibull modulus of materials; also can produce higher heat conductivity, coefficient of thermal expansion and heat-shock resistance.But now there is lacking in the researches of nanotechnology of piezoelectric ceramic structure effecting its properties. To prepare PZT nano-crystal powders with a composition of Pb(Zr_0.52 Ti_0.48)O₃,which is near the morphotropic phase boundary (MPB), the raw materials used were reagent grade lead nitrate [Pb(NO₃)₂],zirconium nitrate hydrate [Zr(NO₃)₄·5H₂O], tetra-butyl titanate [Ti(OC₄H₉)₄],using NaOH as the mineralizes, which use sol-gel method with hydro-thermal treating. And it use conventional oxide sintering method to prepare PZT powders with a identical composition. Powders are characterized by DSC/TGA, FT-IR, XRD, and SEM analysis. Common and nano-phase composite PZT ceramics were prepared which owe homogeneous composition and structure using powders, testing and analyzing elastic modulus, flexural strength, hardness and fracture toughness of PZT ceramics. SEM test of PZT ceramics fracture analyses its fracture mode. Weibull statistics evaluates flexural strength dispersibility of PZT ceramics. It also studies that polarization impacts strength in different direction with R curve analysis.DSC/TGA, FT-IR, XRD, and SEM results indicate: PZT nano-phase started to form at as low as 220℃,while phase-pure PZT powders were obtained at 270℃for 2h, its grain size is about 25nm. The piezoelectric testing results of nano-phase composite PZT ceramics indicate that performance date of electromechanical coupling coefficient, dielectric constant and piezoelectric coefficient is not below that of common PZT ceramics. The test results of mechanical properties indicate: elastic modulus is much higher than that of common PZT ceramics, with increasing about 36%. Flexural strength of nano-phase composite PZT ceramics is much higher than that of common PZT ceramics, with increasing about 29%, as the result of grain boundary strengthening. Hardness of nano-phase composite PZT ceramics is much higher than that of common PZT ceramics at different indentation loading, with indentation size effect. Fracture strength of nano-phase composite PZT ceramics is much higher than that of common PZT ceramics at 5Kg indentation loading, with increasing about 50%. Fracture toughness of nano-phase composite PZT ceramics in polarization state has anisotropy, with that of parallel polarization direction higher than the vertical, owing to its ferroelectric domain structure and mechano-domain transformation. Weibull statistics analysis of flexural strength indicates: common PZT ceramic has a Weibull modulus m=3.59, while nano-phase composite PZT ceramic with a Weibull modulus m=8.167, it also expresses flexural strength of nano-phase composite PZT ceramic fluctuates in a narrower range. SEM test and fractal analysis of PZT ceramics fracture morphology indicate that common PZT ceramic fracture mode is intercrystalline cracking, while nano-phase composite PZT ceramic is intergranular cracking and its fractal dimensionality is higher than that of the intercrystalline,its fractal dimensionality is direct proportional to fracture toughness. It obviously indicates nanotechnology of piezoelectric ceramic structure produces good affecting on its fracture toughness. R curve analysis indicates that resisting force of crack growth in polarization direction increases with crack size increasing, owing to ferroelectric domain deflection. To summarize, this study revealed that nanotechnology of piezoelectric ceramic structure can enhance its mechanical properties greatly on the condition of piezoelectric property is unchanged or slightly enhanced.In brief, nanotechnology of ceramic structure can enhance its mechanical properties greatly, ensuring intrinsic property parameters of piezoelectric ceramic. Therefore we can anticipate that nanotechnology of piezoelectric ceramic structure can enhance its mechanical properties greatly and can prolong service life of its products.