| Ethylene Diamine Tetraacetic Acid （hereafter, abbreviated as EDTA）, as remarkable chelatingagent by combining with the traditional sol-gel method, has been widely used in many fields such asmagnetic material, microwave dielectric ceramics, luminescence materials, superconducting field andso on. Lead-free piezoelectric （K, Na）NbO3bulk ceramic and thin films was first synthesized by thisnovel EDTA assisted sol-gel method. Instead of using NbCl5or other expensive starting materials, weadopted Nb2O5, cheap and more common raw materials, as the Nb source in our research whenpreparaing the （K, Na）NbO3sol. In order to promote the esterfication reaction, citrate acid and ethyleneglycol were used as the chelating and eaterfication agent, respectively. Besides, ammonium oxalate wasalso used to improve the reaction activity of Nb5+. As function of pH, EDTA, and the amount of citrateacid and ethylene glycol, the sol state was systemically investigated in our work.KNbO3nano-powder was first synthesized by the modified sol-gel method, and what’s more, theparticle size was less than100nm. Moreover, by adding extra Na+into the precursor solution,single-phase lead-free piezoelectric （K, Na）NbO3ceramic powder with no secondary or pyrochlorephases was synthesized. The effects of the compensation of K+and annealing temperature on the phasecomposition and morphology were studied systemically. Well-crystallized ceramic powder with goodsintering activity and no agglomeration was synthesized when the K/Nb molar ratio was1.2. Inaddition, the formation mechanism on （K, Na）NbO3perovskite structure as function of annealingtemperature was also investigated.Using the EDTA assisted sol-gel synthesized （K, Na）NbO3powders as raw powders,（K, Na）NbO3piezoelectric ceramics were fabricated via traditional sintering process. The effects of annealingtemperature on the mechanical, piezoelectric and ferroelectric properties were investigated. The mostappropriate sintering temperature was1100oC.The piezoelectric constant d33, remnant polarization Prand electric field Ecreached about88pC/N,17.148μC/cm2and0.974kV/cm, respectively. Comparing with the solid-state reaction method, the （K,Na）NbO3ceramics sintered from the modified sol-gel powders feature lower porosity and higherdensity. So the strength of the crystal boundary was increased, and transgranular fracture occurred. Also,the remnant polarization was improved significantly.The （K, Na）NbO3thin films were prepared on the Si substrate by sol-gel method using the above（K, Na）NbO3precursor sol. Additionally,（K, Na）NbO3thin films were also fabricated using NbCl5as Nb source as a reference. And all kinds of test were performed on the final product. Compared withthese two methods, well-crystallized （K, Na）NbO3dense films were synthesized by the former mehod. |
