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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 56382 (07)
- University: Sharif University of Technology
- Department: Materials Science and Engineering
- Advisor(s): Khachatourian, Adrineh Malek; Golmohammad, Mohammad
- Abstract:
- Due to the environmental problems of lead and the prohibition of its use, lead-free piezoceramic sodium-potassium niobate, KNN, are one of the main candidates to replace lead-containing piezoceramics, PZTs. High Curie temperature, low density, and compatibility with nickel electrodes are its distinguishing features from other piezoelectric materials. The crystal structure of this material varies with temperature and includes rhombohedral, orthorhombic, tetragonal, and cubic. Various synthesis and manufacturing methods including hydrothermal, solid-state reaction, sol-gel, molten salt, etc. are used for this material. In this research, the hydrothermal synthesis method is used due to its high purity, micron and submicron particle size, and optimal microstructure. Optimizing the synthesis method and K+/Na+ to reach the morphotropic stoichiometric composition was the first goal of this research. XRD and FESEM analysis revealed that among the three ratios of 15, 10, and 4 for K+/Na+, ratio 10 is the most optimal mode in terms of stoichiometric composition, formed phases, and powder morphology. Modern sintering processes improve the final piezoelectric properties of the material, and flash sintering method was used in this research. The optimization of applied electric current density and sintering time, under the electric field of 250 V/cm and temperature of 950 °C, was investigated as the next goal to determine the optimal main parameters of this method. The results of densitometric analysis, FESEM, elemental mapping, and piezometric analysis showed that in spite of the slight difference between the stoichiometric composition of the synthesized powder and the morphotropic composition, the final piezoelectric properties are acceptable. The highest piezoelectric charge coefficient, equal to 112 pC/N, and the final relative density, 96.01%, were observed in the sample with an applied current of 60 mA (average electric current density of 20.95 mA/mm2) and a flash sintering time of 60 seconds, which turned the conditions of this sample into the final optimum condition
- Keywords:
- Piezoelectric ; Piezoceramic ; Potassium Sodium Niobate ; Nonlead Compounds ; Lead Zirconate Titanate (PZT) ; Piezoelectric Load Factor ; Flash Sintering
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