Investigation of the Structural and Microstructural Characteristics of Sol-Gel Derived Lead Lanthanum Titanate Thin Film
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Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
propoxide, in stoichiometric proportion, was dissolved in methoxy-ethanol. A calculated amount of lanthanum methoxide was separately dissolved in methoxy-ethanol and added drop-wise to the Ti sol with continuous stirring at room temperature for 5 minutes. The La-Ti complex sol was added to Pb-acetate solution at 90 0 C with continuous stirring for about 20 minutes to prepare the parent sol. The preparation methodology of the acetic acid modified precursor was almost identical to that of the methoxy-ethanol based route, except in this case the solvent was acetic acid, and lanthanum acetate was used as the precursor material for La doping. Prior to deposition the parent sol was diluted to 0.4 M concentration with the addition of either acetic acid or methoxy-ethanol and spin-coated coated on cleaned substrates at 3000 r.p.m. for 20s. Just after deposition, the films were directly inserted in a preheated furnace kept at a temperature ranging from 3500C to 650 0 C, heated for 5 minutes, and then quenched in ambient air. The coating and firing cycles were repeated for 10-20 times to increase the film thickness (uptol rtm), and finally, 0
the films were annealed at 700 C for 1 hour in oxygen ambient followed by rapid quench to
room temperature. Thermal analysis of PLT gel powders was performed using a differential scanning calorimeter (DSC-50, Shimadzu Corporation). Heating rates in the range of 10-25°Cmin- I were used in these measurements. The phase formation behavior was studied by X-ray diffraction (D5000. Siemens). The surface morphology of the films was characterized by an atomic force microscope (Nanoscope I11a, Digital Instruments). Raman measurements were performed using a Jobin-Yvon T64000 spectrophotometer consisting of a double monochromator coupled to a third monochromator/spectrograph with 1800 grooves/mm grating. Sputtered circular gold electrodes (0-200 utm) were used as top electrodes for the dielectric and ferroelectric measurements. The frequency dispersion of relative dielectric constant and loss tangent were measured using an impedance analyzer (4294 A, Hewlett Packard) with an oscillating voltage of 500 mV. The P-E hysteresis loops were measured at 20 Hz using a commercially available hysteresis loop tester (RT 6000 HVS, Radiant Technologies). RESULTS AND DISCUSSION Phase formation kinetics The DSC plot of PT xerogel dried at 800 C indicated two exothermic features at =300 0 C and 5000C respectively. From the analysis of IR spectra and the X-ray diffractograms of PT gel heat treated in a temperature range (200-700 0 C), we identified that the peak at -300 0 C is due to the pyrolysis of residual organics and the second exothermic peak was due to the crystallization of amorphous gel. The DSC data were recorded at different heating rates and it was observed that the crystallization peaks were shifted to higher temperature as the heating rate was progressively increased (Fig.l). The temperature corresponding the crystallization pe
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