| A series of La1-xCaxMnO3with perovskite structure has been extensively investigated as an important material because of its Colossal Magnetoresistance (CMR) effects. These materials have attracted much attention due to their significant technological applications in optical, electrical, and magnetic devices. Much effort has been expended on methods to synthesize the nanostructure materials. Up to now, the synthesis of these materials has been remained challenging.In this thesis, the La1-xCaxMnO3(x=0.0-1.0) powders and polycrystalline targets were synthesized by Sol-Gel and chemical co-precipitation methods. In the Sol-Gel method, La1-xCaxMnO3powder was obtained at as low as550℃without any intermediate step. In comparison to Sol-Gel method, La1-xCaxMno3polycrystalline targets were prepared by co-precipitation method, in which it was needed900℃calcined temperature to get single perovskite phase. It has been found that Sol-Gel method is more effective and power consuming than co-precipitation method. The electrical transport properties are also better.The structures of the prepared polycrystalline LCMO targets have been characterized by X-ray diffraction (XRD) method. X-ray diffraction patterns demonstrate that all the samples have single perovskite phase and orthorhombic Pnma crystal symmetry. The morphology of bulk polycrystalline LCMO targets and their electrical transport measurements were performed by using scanning electron microscope (SEM) and conventional four probe technique. The p-T curves of the prepared bulk La1-xCaxMno3showed different transport behavior, while Ca contents x<0.2showed insulating behavior,0.2<x<0.4show both insulating and metallic behavior and x>0.5show insulating behavior.Pulsed Laser Deposition (PLD) technique has been used to fabricate LCMO epitaxial thin films on single crystalline15°tilted and untilted LaALo3(100) substrates. The deposition condition for La1-xCaxMnO3(0<x<1) thin films are studied and optimized. All the films were grown under the oxygen pressure of100Pa at790℃for10min and then annealed at30000Pa at760℃for30min, the frequency of KrF excimer laser (λ=248nm) with a repetition rate of5Hz. The laser energy density irradiated on the targets was1.6J/cm2. The prepared thin films were structurally characterized by XRD and AFM, electrical transport properties were studied by R-T measurement and the correlation between Ca doping levels and Laser induced voltage (LIV) signals were also studied.The analysis of (θ-2θ) X-ray diffraction and rocking curve showed that all the films deposited on untilted substrates were single perovskite phase and c-oriented with good crystalline quality. The films deposited on tilted substrates also show only LCMO (100) reflection peaks, the AFM results demonstrated that the surface roughness increased with increasing Ca doping levels, further, homogeneous structure can be observed in all films. It was found that electrical transport properties of the prepared thin films are quite different from bulk materials; this may be due to the strain effect results from the misfit between film and substrate and the oxygen deficiency, etc. LIV effect was found in the films grown on the15°tilted substrates. The peak value of LIV signal (Up) firstly increased with increasing Ca content and arrived to its maximum at Ca content x=0.5and then decrease. The respond time was found decrease with the Ca content increase. Jahn-Teller distortion and microstructure of film may be attributed to this tendency. At x=0.5, the highest peak value of LIV signal (Up)744mV with the time respond (τ)147nm and figure of merit (Fm) is5.1was acquired. |
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