Effect of Sol-gel Coating on Microstructure and Electrical Properties of Microwave Garnets

Abstract

ABSTRACTMicrowave magnetic properties of Gd substituted yttrium iron garnets are known to depend on their microstructural characteristics such as porosity and grain size. Surface coating of the garnet powders through a gelation of Si and Mn organic solution was conducted to inhibit the grain boundary movement during sintering with considerable densification. High density and uniform microstructure were obtained after sintering at 1400°C in O2 atmosphere. Grain growth kinetics were studied with variation in sintering time as a function of grain size. An activation energy of 102.9 kcal/mol was obtained for grain growth of the sol-gel coated sample. Grain boundary region was investigated by using TEM and EDS. A very thin grain boundary layer was observed with Si segregation in the region. Electrical resistivity at 100 Hz was 1.46×109 Ωcm for the sol-gel coated sample sintered at 1400°C for 3hrs in O2. Above results were discussed and compared with those obtained by the conventional batch mixing of additives.