الفهرس 
Theoretical considerationsOnly 14 pages are availabe for public view
 |  | from | 122 |  |  |
| | | from | 122 | | |
Abstract
The aim of the present work i s to study some of the transport properties of mixed ferri tes for d i f f e r e n t compositions CuFe Cr 0 where x= 0.0.- 0 . 2 , 0 . 4 , 0.6, and 2-x x 4 0 . 8 . The samples were prepared using the ceramic method. They are pressed into disc form under constant pressure of about 5 2 0 ton/cm and f i n a l l y sintered a t 1150 c for 6 hours. The prepared samples were i d e n t i f i e d by x-ray d i f f r a c t i o n method, and the l a t t i c e parameters were calculated. Some physical properties such as experimental densi t y , X-ray densi t y and porosi t y are calculated. The thermoelectric power and the rrsisti vi ty was determined a t differem t- i-c-rnpe1.a t - u r ~ n F t ~ r - J i samples. The a. c. conductivity and the ’ d i e l e c t r i c constant were 2 measured for all samples a t different frequencies f r o m 20 to 5 10 Hz and a t d i f f e r e n t temperatures from room temperature up 550 K. It- was found that:; All compositions were found to have tetraqonal spinel structure. The lattice parameter, a , increase2 w h i l e the . f a t t f c c parameter, c, decreases both with increasing Crsdbsti tution. The experimental density increased while the porosity decreased both with increasing Cr-substi tution. The theoretical density i s greater than the experimental density for a1 1 samples. A t romm tenlperqture the thermovol tage was negative formost samples. This indicates that: t-he ma jr?ri t y i : t ~ . r . r ~ PI.:^ j n fhpse .qamples a r e elect.rons . A t room temperature the thermovol taqe i s positive f o r sample CuCr Fe 0 . This indicates that the majority 0.8 * . 2 4 carriers are holes which decreasrs wi th imcz-eaaing ,I The r e s i s t i v i t y increases with increasing Cr-substitution a t room temperature . D. C. r e s i s t i v i t y decreases wi th increasing tempera tiire qi vinq semiconducting behaviour. The activation energy for e l e c t r i c conduction increases during transition from ferrimagnetic s t a t e into paramaqne t i c s t a t e , and the difference between the two activation enerqies increases with increasinq Cr-substi tution, The transi ti on temperature (Curie temperature) increases with increasing ~ r - s u b s t i t u t i o n . the mobility was calculated for samples x = 0.0, 0 . 2 , 0 . 4 , and 0.6 at d i f f e r e n t temperatures. I t i s found t h a t the mobil i t y increases with increasing temperature and it decrease as C’r-content increases. The mobil i t y is rang-ed 2 -i -1 from 16’ to cm . vol t sec . The activation energy for mobility i s calcuiated for s = 0 . 0 , 0.2, 0.4 and 0.6 and it i s found to be 0.18, 0.3, 0.24 and 0.42 ev respectively. The a . c. conducti vi t y increases wi th increasing both the frequency and temperature lower than Curie point, while i t becomes frequency independent- at temperatures higher than Curie temperature. The activation energy for a . c. conduct:i vi t y in paramagnetic state is h i y h e r than t h a t i n f ~ r l - - i m : r n e t i c s t a t ? . the pure a . c . component of the measured a . c, conducti vi t y is s e y a r , ~ fed arid i f is forlntl to be i t cfp;,c-.rrclt:rr t according to the law rj a = A w ac where n, A are constants and w i s the angular frequency. l’he constant n is det-ermined for acme sdrlrrpia:; aari i t rv.q.- found to be l e s s than unity. he d i e l e c t r i c constant decreases with increasing both , frequency and Cr-substitution a t room temperature. W i th increasing the frequency the die1 e c t r i c constant exhibits a dispersion peak which i s shifted towards the higher frequencies with increasinq the temperature. the d i e l e c t r i c loss was determined a t d i f f e r e n t frequencies a t room temperature, and it was f o t i ~ d to be decreased with increasinq the frequency and Cr-substi tution. The d i e l e c t r i c behaviour was discussed in l i g h t o f the presence of both p- and n-types of charpr carriers.