TAILIEUCHUNG - Báo cáo " MODEL OF CONDUCTIVITY FOR PEROVSKITES BASED ON THE SCALING PROPERTY OF GRAIN BOUNDARY "

We present the percolation-theory model for explanation of conductivity of perovskites based on the scaling property of grain boundary formation. Assuming a two-layer simple effective medium model, composed of the grain itself as a first layer and the boundary as a second layer, it was modeled that the net resistivity r of the medium depends on the average grain size L, boundary thickness L’ and boundary fractal dimension D. | VNU. JOURNAL OF SCIENCE Mathematics - Physics. N04 - 2005 MODEL OF CONDUCTIVITY FOR PEROVSKITES BASED ON THE SCALING PROPERTY OF GRAIN BOUNDARY Phung Quoc Thanh Hoang Nam Nhat Bach Thanh Cong Department of Physics College of Sciences - VNU Abstract. We present the percolation-theory model for explanation of conductivity of perovskites based on the scaling property of grain boundary formation. Assuming a two-layer simple effective medium model composed of the grain itself as a first layer and the boundary as a second layer it was modeled that the net resistivity r of the medium depends on the average grain size L boundary thickness L and boundary fractal dimension D. The obtained formula was tested specifically for the perovskite system x and whose structures and electric properties were reported earlier by these authors VNU J. of Sci. XX AP 2004 p. 130-132 . The determination of fractal dimension was based on the standard length-area technique and was carried out using SEM images which were photographed at three magnification scales 2 5 and 10 m. This dimension showed good correspondence to the small polaron hoping energy in high temperature region and gave very good fits to experimental data for T TN. Perovskite Structure Fractal Grain Boundary Conductivity PACS . n Fractals - Grains - Crystal structure and defects 1. Introduction The application of the fractal techniques to study the conduction mechanism in the perovskite superconductors 1-3 is not new but for the manganate perovskites there is a lack of studies dealing directly with the grain boundary conductivity. We know only one work from Dobrescu et al. reporting the fractal dimension determination for Lai-xSrxCoOs 4 . Although many studies showed the essential effects of grain boundary on the macroscopic resistivity of perovskite 5 up-to-date there is still absent the knowledge about the boundary geometry. For the perovskites one .

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