الفهرس 
Theoretical considerationsOnly 14 pages are availabe for public view
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Abstract
The aim of the present work is to study the physical properties of Ni-A1 ferrites. Samples of the type NiFea-, Alx 04 were prepared, using ceramic technique (where X = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), prossed into disc form under constant pressure and finally sintered at 1300 OC for 6 hours. The prepared samples were identified by X-ray diffraction method. It was found to have cubic spinel structure and lattice constant was calculated for each. Some physical properties such as experimental density, theoretical density and porosity. Resistivity and thermoelectric power have been studied under vacuum in a wide range of temperature from room temperature up to about 900•‹K. The dielectric constant and dielectric loss have been measured as a function of frequency at room temperature. The temperature dependence of dielectric constant has been measured for some samples. Concl usions1 1- The lattice constant decreases with increasing aluminium content in samples. 2- The experimental density is smaller than theoretical density, as expected, and both are decreasing with increasing of aluminium content, while porosity increases. 3- The conductivity in these samples is due to hopping conduction mechanism of electrons and holes. 4- The activation energy for conduction process increases C47 during transition from ferrimagnetic to the paramagnetic state. These increments ranged between 0.07 and 0.1 eV. 5- Measurements of thermoelectric power show that the conduction occurs by electrons due to the exchange of electrons between Fe3+and Fea+ions in octahedral sites and by holes due to exchange of holes between Nia+and Ni 3+ions. 6- The transition temperature from ferrimagnetic to paramagnetic state (Curie temperature) decreases linearly with increasing aluminium content. 7- The calculated mobilities of the electrons of this samples ranged from 10-4to 10-6cma /V.S at room temperature and increases exponentially with temperature, this behaviour is characteristic for the - 61- hopping conduction mechanism. The dielectric loss (tan 6) decreases with increasing the frequency at room temperature. The dielectric dispersion was observed (€IF). The position of the peak shifts two lower frequency with increasing aluminium content. Temperature dependence on dielectric constant at different frequency shows that the peak (E’r) max. shifted to higher 6Lq~ by increasing C ”5: .This behaviour of dielectric is attributed to the presence of n and p carriers.