ROLE OF GADOLINIUM DOPANT IN GD3XY3(1-X)FE5O12 FERRITE GARNET THROUGH PHASE CONVERSION MODELING AS THE BASE OF MICROWAVE RESPONSE

• Main Author: Subawi, Handoko
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/65139
• Institution: Institut Teknologi Bandung

This study of yttrium iron garnet (YIG)-based ferrite garnet was chosen because YIG garnet plays an important role as a circulator component in microwave radar and telecommunications equipment. Although YIG garnet showed positive results in the microwave response test, it was considered unsatisfactory so that improvements were needed. An understanding of the sintering conditions is needed to determine its benefits for the formation of the dominant phase. The steps of the YIG sintering reaction with rare-earth doping, need to be confirmed through phase conversion modeling to determine the effective pattern of formation of the ferrite dominant phase. The rare earth element chosen in this research is gadolinium which has seven unpaired electrons. Gadolinium doping is used as the basis for microwave response with the benefit of being able to significantly reduce insertion loss. Experiments were carried out by considering several factors before and during the sintering process. The sample preparation method begins with setting the composition between Fe2O3, Y2O3 and Gd2O3 quality > 99% (pure grade) using a digital scale. The compound mixture is then hydraulically compacted by dry pressing before the sintering process is carried out in the furnace. High purity solid oxide compounds with small and uniform sizes facilitate the hydraulic compaction step in the formation of green pellets. The sample density indicator was based on the densification parameter, while the phase morphology that appears in the microstructure is based on images obtained using an optical microscope and SEM. The sintering operating conditions were adjusted to obtain the dominant phase ferrite, considering the information obtained from the literature data. The application of the right sintering temperature and time facilitates the formation of the dominant phase and anticipates the presence of the secondary phase. The dominant phase sintering reaction makes the compound reaction mechanism simpler because it does not involve a secondary phase reaction. The reaction steps during the sintering process were confirmed through phase conversion modeling to ensure the achievement of the ferrite dominant phase formation. Potential presence of undesired impurity and secondary phases, identified from X-RD diffractogram. The magnetic characterization from the hysteresis loop was obtained from the Remacomp test. The performance of microwave response is predicted theoretically based on the composition of gadolinium doping on YIG. The insertion loss value from the calculation results is validated through a microwave response test using a vector network analyzer. The X-RD analysis identified the experimental sample as the product of the dominant phase, where gadolinium doping accelerated the formation of the dominant phase. The OM and SEM images show the surface appearance of the sample after sintering, while the density level is identified through the densification parameter. The measurement tests resulted YIG value of 73.3% (> 70%). This research proves that the shrinking core model as a phase conversion model best describes the role of Gd doping in Gd3xY3(1-x)Fe5O12, where the sintering reaction takes place in two stages through the formation of an unstable perovskite. The microwave response test of Gd3xY3(1-x)Fe5O12 with gadolinium doping 14.3–25.3% mol, produces an insertion loss value close zero. This is in accordance with the measurement results of insertion loss YIG (Gd 15% mol) of 0.24 dB. This insertion loss value shows a very significant improvement compared to the microwave response performance of pure yttrium iron garnet (without gadolinium doping) with an average value of 5.51 dB. Overall, this research proves that gadolinium doping plays an important role in improving the microwave response performance of yttrium iron garnet compounds.