FERRITES IN MICROWAVE APPLICATIONS 



1303 



FERRITE COMPOSITION AND IRON STOICHIOMETRY 



There is a continuous program of measurement in which a large 

 number of ferrites from various sources are tested at X-Band and other 

 frequencies. In the early days of the program the most remarkable feature 

 of the results was the tremendous variation in properties even among 

 materials of supposedly the same composition. More recently some 

 general trends have been observed, and it is now possible to correlate the 

 microwave performance of certain types of ferrites with their chemi- 

 cal and structural nature. The nickel-zinc ferrites in particular have 

 been studied extensively, and those having the approximate formula 

 Nio.3Zno.7Fe204 are quite good for microwave applications so long as 

 they have slightly less iron than the above formula requires. A series 

 of measurements illustrating the effect of slight variations in iron content 

 yielded the data shown in Figs. 18 and 19. These ferrites were prepared 

 by F. J. Schnettler of Bell Telephone Laboratories in such a way that 

 their bulk properties correspond very closely to their crystallite proper- 

 ties. The correspondence between the bulk dc conductivity and the RF 



-001 0X)1 0X)2 0.03 



IRON EXCESS OR DEFICIENCY IN ATOMS PER MOLECULE 



Fig. 18 — DC conductivity versus iron content of NiZn ferrite. 



