The effect of Zr-substitution on the physical and magnetic properties of Li 0.3+0.5x Zn 0.4 Zr x Fe 2.3-1.5x O 4 ferrites (x=0.0, 0.01, 0.02, 0.03 and 0.05), prepared by the standard ceramic method, has been studied. It is found that the saturation magnetization increases up to x=0.02 and then it decreases. On the other hand, the initial permeability increased while the Curie temperature remained almost constant with increasing x. The behavior of coercivity and remanence ratio was discussed. The composition dependence of the dc electrical resistivity is found to support the hopping conduction mechanism.
Thermoelectric power (α) and electrical resistivity (ϱ) measurements are made for the mixed inverse system CuxCo1−xFe2O4 with x = 0, 0.25, 0.5, 0.75, and 1. The measurements are done from room temperature up to 600 K. It is found that all samples are n‐type semiconductors with activation energy varying from 0.59 to 0.21 eV for different samples. The activation energy plot shows a maximum at x = 0.5. The drift mobility of charge carriers (μd) is calculated at different temperatures. From the values of μd and the temperature dependence of both, (α) and (ϱ) it is suggested that the transport properties measured may be interpreted using the localized model of electron (polarons).
Two types of carbon black namely fast extrusion furnace black (FEF) and high abrasion furnace black (HAF) were incorporated with a concentration of 50 phr into styrene butadiene rubber (SBR) and natural rubber (NR). The effect of the time of aging and temperature on the electrical conductivity was studied. It was found that a thermal aging at 95 "C leads to the appearance of minimum in conductivity ((I) in both FEF/NR and HAF/NR. This was explained by a competition between two factors: degradation and increase of crosslinking density in the rubber matrix. In case of FEF/SBR and HAF/SBR it seems that these factors have comparable effects on the conductivity after 10 days of aging. From the current-voltage (I-V) characteristics the carrier concentration, trap density, and the drift mobility were calculated. The minimum found in the temperature dependence of (I for FEF/NR is discussed and found to be controlled by the relative dimension of carbon and rubber aggregates.
ZUSAMMENFASSUNG:Zwei Typen von RuB ,,fast extrusion furnace black" (FEF) und ,,high abrasion furnace black" (HAF) wurden mit einer Konzentration von 50 Teilen pro 100 Teilen in Styrol/Butadien-und Naturkautschuk eingebaut. Der EinfluB der Zeit, der Alterung und der Temperatur auf die elektrische Leitfahigkeit wurde untersucht. Es zeigte sich, daD eine thermische Alterung bei 95 "C zu einem Minimum in der Leitfahigkeit (a) bei beiden Proben FEF/NR und HAF/NR fuhrte. Dieses wurde mit einer Konkurrenzreaktion zwischen zwei Faktoren erklart: Abbau und Anstieg der Vernetzungsdichte in der Kautschukmatrix. Im Falle von FEF/SBR und HAF/SBR zeigen diese Faktoren vergleichbare Effekte auf die Leitfiihigkeit nach 10 Tagen Alterung. Aus den Strom-Spannungscharakteristiken (I-V) wurden die Tragerkonzentration, Haftstellendichte und Driftbeweglichkeit berechnet. Das fur die Temperaturabhilngigkeit gefundene Minimum der Leitfiihigkeit von FEF/NR wird diskutiert, wobei sich herausstellte, daD sie von der relativen GroDe der Kohlenstoff-und Kautschukaggregate kontrolliert wird. 0 1985 Hiithig & Wepf Verlag, Basel
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