(La _0.67 Ca _0.33-y Sr _Y MnO <3> _{1-X < Preparation Of Ag X Materials And Study On Their Electrical Properties}

The perovskite manganite oxide La1-xCaxMnO3(LCMO) with metal-insulator (R-T) transition and colossal magneto-resistance(MR) effect near the Curie temperature, caused by its competition of internal mechanism, is the basis of infrared detector, magnetic storage device and magnetic detector with high performance.In this thesis, firstly we prepared (La0.67Ca0.33-ySryMnO3)1-x:Agx (x=0.00,0.05,0.10,0.15, 0.20,0.25,0.30,0.40,0.50;y=0.00,0.02,0.04,0.06,0.08) polycrystalline ceramics by sol-gel technique. Through changing the Ag-adding, calcining temperature and Sr-doping to obtain the polycrystalline ceramics samples with excellent electrical performance. Secondly, the (La0.67Ca0.33MnO3)1-x:Ag(sample with best performance were selected as target to prepare thin films on LAO substrate in different laser energy, growth temperature, oxygen pressure, annealing temperature and annealing oxygen pressure, using pulse laser deposition (PLD). The crystalline structure, surface morphologies and electrical properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), resistance-temperature (R-T) and magneto-resistance (MR) measurement. And the the elements contents and valence state were investigated by inductively coupled plasma optical emission spectrometer (ICP) and X-ray photoelectron spectroscopy (XPS) measurement.The results showed that, with the Ag addition increased gradually, the resistivity (p) decreased and metal-insulator transition temperature (Tp) shifted from 270K (x=0.00) to 281K (x=0.60); and the temperature coefficients of resistance (TCR) values first increase and then decrease, the maximal TCR=58.6%·K-1 is obtained at x=0.15; the magneto-resistance (MR) effect is enhanced at the beginning and then weakened, the maximal|MR|=74%·K-1 is obtained at x=0.25. This could be attributed to the change of lattice constant, sintering quality and grain boundary caused by Ag-adding. The ICP and XPS measurements results suggest a little Ag reserved in LCMO crystal lattice and substituted for La or Ca, which leads to lattice expansion. The electrical performance of LCMO improved at the beginning and then deteriorated with the calcining temperature rise gradually from 300℃ to 1000℃, and the best sample is obtained at 500℃, which is related to the extent of organic matter decomposition. As the amount of Sr-dopping increases gradually from 0.00 to 0.08, the Tp increases linearly even more than 320K at y= 0.08, while the TCR decreases. This is closely related to the enhancement of double-exchange between Mn3+ and Mn4+ results from Sr-dopping.Different preferred orientation growth of films is attributed to different deposition technology. The best properties (TP=293K and TCR=11%) of the film is obtained at laser energy 350mJ, growth temperature 750℃, annealing temperature 900℃ and annealing oxygen pressure 10~5 Pa.