Thermal diffusivity of NTC layers obtained with photoacoustic technique

The thermal diffusivity of thick film NTC layers based on a metal oxide powder mixture was measured at room temperature by the photoacoustic (PA) technique. The powder mixture was composed of MnO (60 percent), CoO (32 percent) and Fe2O3 (8 percent), which were ball milled to nanometer particle size. NTC layers of different thicknesses were made by sequentional screen-printing followed by drying and co-firing at 850, 900 and 1,000degreesC in a hybrid conveyor furnace. The experimental PA phase and amplitude diagrams were numerically analyzed and the thermal diffusivity and electron transport parameters were calculated. An increase of thermal diffusivity with sintering temperature was observed. The fractal structure model was in agreement with the experimental data for modulation frequencies in which the sample behaved as thermally thick.