Bahan yang memiliki sifat ferroelektrik dan ferromagnetik berpotensi sebagai absorber gelombang mikro dan memiliki peranan penting pada dunia militer. BiFeO3 merupakan salah satu bahan multiferroik yang memiliki sifat ferroelektrik dan ferromagnetik. Pada penelitian ini dilakukan rekayasa sintesa BiFeO3 dengan doping Yttrium dan Seng dengan variasi konsentrasi (%wt) 6, 12, dan 18%. Sintesa BiFeO3 telah berhasil disintesis dengan metode sol-gel autocombustion. Melalui uji XRD, fasa BiFeO3 diperoleh pada temperatur 750°C selama 5 jam. Hasil refinement menunjukkan bahwa BiFeO3 memiliki struktur kristal rhombohedral space grup R3c. BiFeO3 doping Yttrium dan Seng di atas 12% (%wt) terjadi perubahan struktur kristal dari rhombohedral ke orthorombic. Kurva hysterisis menunjukkan bahwa BiFeO3 memiliki saturasi magnetik 3.04 emu/g, remanen magnetik 0.26 emu/g, dan medan koersivitas 0.0013 T. BiFeO3 doping Yttrium dengan konsentrasi (%wt) 12% terjadi peningkatan nilai saturasi magnetik, remanen magnetik, dan medan koersivitas namun BiFeO3 doping Seng dengan konsentrasi (%wt) 12% terjadi penurunan nilai saturasi magnetik, remanen magnetik, dan medan koersivitas. BiFeO3 doping Yttrium 12% (%wt) dan Seng 12% (%wt) memiliki nilai saturasi magnetik 8.18 emu/g, remanen magnetik 2.92 emu/g, medan koersivitas 0.0036 T. Pada frekuensi 1 kHz BiFeO3 memiliki konstanta dielektrik sebesar 239.12 dan adanya doping Yttrium dan Seng terjadi penurunan nilai konstanta dielektrik. Hasil pengujian sifat penyerapan gelombang mikro pada frekuensi X band (8.2 ? 12.4 GHz) diperoleh bahwa bahan Bi0.88Y0.12FeO3/C memiliki refleksi loss -39.42 dB pada frekuensi resonansi 11.47 GHz. Dengan demikian bahan Bi0.88Y0.12FeO3/C dapat dijadikan bahan penyerap gelombang mikro pada frekuensi X band.

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Materials with both ferroelectric and ferromagnetic properties are potential candidate for microwave absorbers and play important role in military world. One of them is BiFeO3, a multiferroic material with both ferroelectric and ferromagnetic properties. In this research, BiFeO3 has been synthesized successfully via auto-combustion sol-gel method. To improve its properties, yttrium- and zinc-doped BiFeO3 has been synthesized with various doping concentrations, i.e. 6, 12, and 18 wt.%. X-ray diffraction patterns showed that BiFeO3 phase was obtained after heating at 750ᵒC for 5 hours with rhombohedral crystal structure and space group of R3c. The hysteresis curve of BiFeO3 showed a magnetic saturation of 3.04 emu/g, magnetic remnant 0.26 emu/g and coercive field 0.0013 T. Yttrium- and zinc-doped BiFeO3 over 12wt.% showed a structural change from rhombohedral to orthorhombic with magnetic saturation of 8.18 emu/g, the magnetic remnant of 2.92 emu/g and coercive field of 0.0036 T. Yttrium-doped BiFeO3 showed an increase in the magnetic saturation, the magnetic remnant and the coercive field; however zinc-doped BiFeO3 showed a decrease in the magnetic saturation, the magnetic remnant and coercive field. At a frequency of 1 kHz, the dielectric constant of BiFeO3 was 239.12, and this value will decrease when it was doped by yttrium and zinc. Further investigation on the application of this material, composites Bi0.88Y0.12FeO3/C has also been synthesized. The composites showed a reflection loss of -39.32 dB within the frequency range of 8.2-12.4 GHz (X-band) particularly at the frequency of 11.47 GHz with the absorptivity of 98.60%. Based on this results, composite Bi0.88Y0.12FeO3/C material could be used as a potential microwave absorber in the X-band frequency.