The The Lpmo Film Litv Effects And Non-ohmic Behavior In The Lcmo Film

The perovskite manganites La_1-xA_xMnO₃ (A: Sr, Ca, Ba, Pb) have been attracted great attention and investigated deeply due to their colossal magnetoresistance (CMR) effect in recent 10 years or more. In 1999 years, the laser induced thermoelectric voltages (LITV) effect was found in LaCaMnO₃ thin films grown on vicinal-cut LaAlOi substrate by P. X. Zhang, etal, which broadens the applications and studies of manganites.In this thesis, the series of La_0.67Pb_0.33MnO₃ (LPMO) polycrystals doped with silver were prepared using coprecipitation method. LPMO thin films were prepared using pulse laser deposition (PLD) technique. The X-ray diffraction results show that LPMO polycrystals and thin films are all of single phase with pseudo-cubic symmetry. For the first time, the LITV effect was observed in this compound. LPMO thin films were grown with different deposition conditions and different silver doping level. A comparison study on the LITV effects ofLaCaMnO₃ and of LaPbMnO₃ shows: 1, the response time of LITV signal in LaPbMnO₃ is faster than that of LaCaMnO₃;2, the time dependence of LITV of LaPbMnO₃ also obeys the formula deduced by G Y. Zhang etal;3. A relation was found between the response time of LITV signal and the resistivity of LaPbMnO₃ thin films;4, It was found that the peak voltage and the response time of LITV also depend on the thickness of LaPbMnO₃ film, and optimal thickness exists when the shortest response time is obtained;5. The response time of LITV signals of thin film can be reduced by post annealing with high oxygen pressure and high temperature.To study the nonohmic behavior, La_0.67Ca_0.33MnO₃-Ag 4 wt% thin films of different thickness were prepared in different depositiom time by PLD technique. The temperature dependence of resistivity of the films was measured using four-probe method with different currents. The results show: there exists a critical thickness, below which the resistivity at Tp increases and then decrease with the applied current, and above which it displays an opposite behaviors.