Geometrical and electrical properties of NTC polycrystalline thermistors vs. Changes of sintering parameters

NTC thermistor powder was made of a Mn, Ni, Fe and Co oxide mixture calcinated at 1050°C / 60 min. The powder was milled in a ball mill down to an average particle diameter of 0.9 μm. Small disc shaped pills of the powder obtained were made by pressing with a pressure of 2.5 MPa. The pills were sintered in the temperature range of 900-1400 °C for 30-240 min. The volume and specific volume resistivity change were measured as a function of sintering conditions. Microstructure development was observed using a SEM microscope. Using the results obtained, optimization of sintering parameters was performed in order to determine optimal electrical properties of the selected thermistor composition

Investigation of zinc stannate synthesis using photoacoustic spectroscopy

Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200°C with a heating rate of 5°C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained a correlation between thermal diffusivity and experimental conditions as well the samples microstructure characteristics was discussed.

Synthesis of barium-zinc-titanate ceramics

Mixtures of BaCO3, ZnO and TiO2 powders, with molar ratio of 1:2:4, were mechanically activated for 20, 40 and minutes in a planetary ball mill. The resulting powders were compacted into pellets and isothermally sintered at 1250°C for 2h with a heating rate of 10°C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained correlation between thermal diffusivity and experimental conditions, as well the samples microstructure characteristics, was discussed

Structural and electrical properties of Ti doped α-Fe2O3

In this work we have analyzed the effects of Ti doping on structural and electrical properties of α-Fe2O3. When the amount of added Ti (5 wt.%TiO2) was within the solubility degree and XRD, SEM and EDS analysis revealed a homogenous hematite structure, with lattice parameters a= 5.03719(3) Å, c=13.7484(1) Å slightly increased due to incorporation of Ti into the rhombohedral hematite lattice. Higher amounts of Ti (10 wt.%TiO2) resulted in the formation of pseudobrookite, besides hematite, confirmed by SEM and EDS analysis. Studies of electric properties in the temperature range 25-225oC at different frequencies (100 - 1Mz) showed that Ti doping improved electrical conductivity. Impedance analysis was performed using an equivalent circuit, showing one relaxation process and suggesting dominant grain boundary contribution. [Projekat Ministarstva nauke Republike Srbije, br. III45014 i br. III43008

Thermoelastic and electronic strain contributions to the frequency transmission photoacousticeffect in semiconductors

The photoacoustic effect is investigated as a function of the modulation frequency in a transmission detection configuration for semiconductor samples. The theoretical model for this configuration is given for the thermal and elastic processes besides the carrier-transport characteristics. The dependence of the photoacoustic effect on thermodiffusion, thermoelastic, and electronic-transport parameters is identified. The experimental photoacoustic data for Si samples are tested and they exhibit satisfactory agreement with the theoretical model