| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 97 === There are many compounds of TTB structure shows ferroelecricity, such as Ba2NaNb5O15. Our approach here to change the magnetic property by adding rare earth or trasition metal element, and keep the TTB structure intact.
The focus of research is to synthesize the compound,K2EuxFe1-x+δNb5-0.6δO15 and modulated the ratio between Eu and Fe by solid state sintering as well as sol-gel. Various characterization techniques were empolyed to find the structural changes and its fundamental properties.
The experimental results showed that TTB structure could be prepared at 950 oC in air for 12hr by solid state sintering, but had other compounds at the same time, like Fe2O3. In order to remove Fe2O3, we used hydrochloric acid to wash the powder repeatedly. We find that hydrochloric acid could selectively remove the iron oxide. Hydrochloric acid did not form any new compound, nor did it not destroy the TTB structure. When the Eu to Fe ratio changed, the types of TTB structure also changed as observed from XRD analysis. The number of Fe ion entered the TTB structure is not as good as Eu ion, and we could observer that from the EDS data.
Before the removal of impure phases by hydrochloric acid, the M-T curive contained a step near to 250K. After using hydrochloric acid, the step got disappeared. Compared to every feasible impure phase, we thought the step from the Morin transition is because of Fe2O3. The TTB structure is ferrimagnetic when the nominal composition is K2Eu0.8Fe1.2Nb4.4O15.
Here we also prepared the film by colloidal suspensions method, but observed a large leakage current. Hydrochloric acid was used to avoid impure phases in bulk. Although the problem about leakage current still occurred, but we could observe the trend of polarization by electric field.
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