Synthesis of CMR manganites and ordering phenomena in complex transition metal oxides

Beschreibung

This dissertation covers: the instrumentation development; the optimization synthesis of polycrystalline materials; the single crystal growth of perovskite manganites; the determination of crystal and magnetic structures from x-ray and neutron powder diffraction data of polycrystalline and powdered single-crystalline CMR La1-xSrxMnO3 manganites as well as its application in quantitatively correlating structural and magnetic properties; the application of resonant soft x-ray scattering in the investigation of complex ordering phenomena in La7/8Sr1/8MnO3 and La1Sr2Mn2O7 at the transition metal LII, III-edges and the rare earth MIV, V-edges. Two new devices have been developed: one is the rotating specimen holder for laboratory x-ray powder diffraction, which not only can effectively minimize the problem of preferred orientation but also produces a ‘zero-background’ contribution to the collected data; another is the miniature goniometer for resonant soft x-ray scattering, which makes it feasible to adjust samples along (±2.5°) and (360°) and dramatically improves the efficiency of soft x-ray scattering chambers and can be utilized to unravel the electronic ordering phenomena by resonant soft x-ray scattering. The materials synthesis is the first and critical step for any research in condensed matter physics. One good route has been acquired for preparing high-quality polycrystalline La7/8Sr1/8MnO3 samples, i.e. two times calcining and two times sintering, through exploring various preparation parameters. This synthesis route can be also used to prepare high-quality La1Sr2Mn2O7 and La0.83Ca0.17MnO3. Thus it is a universal one for the present testing. The route for optimizing the synthesis of polycrystalline manganites has been established. One method for preparing straight and very uniformly densified feed rods with a homogenous composition distribution has been acquired, which makes growing large high-quality single crystals possible ...

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Haifeng Li

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CMR CTMO Complex transition metal oxides

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