| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 90 === Abstract
From the past literature we know that it is not easy to obtain the single phase Sr2FeMoO6. In this study we discussed the formation mechanism of Sr2FeMoO6 in the air and reduced stream. Furthermore, we also performed the magnetic、resistivity behavior and structural variation with the doping content of Mo ion .
Stoichiometric powder of SrCO3, Fe2O3 and MoO3 were mixed with ball-milling, the mixture was then calcined at different temperature for 3 hours in air and reduced stream respectively. We found that in air the Mo5+ has a solubility limitation in Sr2FeO3-x matrix. From the viewpoint of radius, both the radius of Mo5+(75.0 pm) and Fe3+(78.5 pm) are larger than Fe4+(72.5 pm), it will lead to lattice distortion when Mo5+ substitutes for Fe4+. If the sample was treated in reduced stream, the oxygen vacancies in the SrFeO3-x matrix increase and allow Mo5+ to diffuse into Sr2FeO3-x successfully. From the synthetic process, SrMoO4 first generated below 500℃ even though the ball-milling process, and then it leads to the diffusion distance of Mo5+ is too large to synthesize the single phase Sr2FeMoO6. We can obtain the tight packing bulk by CIP process. And then we get excellent single phase Sr2FeMoO6 through direct reaction and sintering in reduced stream.
Finally, we compare the magnetization and resistivity with different doping content of Mo in Sr2Fe2-xMoxO6-δ. The Fe3+(3d5)-O2--Mo5+(4d1) antiferromagnetically coupling leads to a net magnetic moment of 4μB/f.u. . However the magnetization decreases when Mo doping content was less than Fe ion. Because Mo5+(4d1) with large orbital extending to the neighbors, the sufficient overlapping can occur through the linkage of Fe3+-O2--Mo5+ and then form a narrow band results in the metallic conduction in Sr2FeMoO6. With Mo doping content decreases, the electrical property shows the semiconductive behavior due to the increasing of Fe3+-O2--Fe3+ couple and then lacks overlapping orbital between Fe ions.
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