<p>Electromagnetic wave is an energy flow in the form of electric and magnetic field as the technology development causes electromagnetic wave exposure level changes significantly and resulting an electromagnetic wave radiation that leads bad impacts on human health. In this case, manganite perovskite became an interesting topic of study that aims to produce material engineering to obtain a material with the best property as absorber. This study is based on lanthanum manganite La<sub>0.7</sub>Ca<sub>0.3</sub>Mn<sub>1-x</sub>Ti<sub>x</sub>O<sub>3</sub> ( and ) using sol-gel method with the with a heating temperature in the oven of 200<sup>o</sup>C for 2 hours, calcination temperature of 600<sup>o</sup>C for 6 hours, and sintering temperature of 1000<sup>o</sup>C for 12 hours. The sample is characterized using X-Ray Diffraction (XRD) that shows the sample had succeeded to form single phase and had crystal cubic structure with space group p m -3 m, the substitution of Ti<sup>3+</sup>ions did not cause the structural changes, but it was marked with the changes of lattice parameter, unit cell volume and average crystallite size. Meanwhile Vector Network Analyzer (VNA) on the frequency range 8-12 GHz shows that the sample has ability to absorb microwave until 90.16% on 10.4 GHz frequency. Therefore, the material based on lanthanum manganite La<sub>0.7</sub>Ca<sub>0.3</sub>Mn<sub>1-x</sub>Ti<sub>x</sub>O<sub>3</sub>has the potential as the microwave absorber material.</p>
Sulawesi Island is composed of complex tectonic arrangements. Most earthquake activities in Sulawesi are affected by the Palu - Koro Fault and Matano Fault. Palu - Koro Fault and Matano Fault are one of the faults in Central Sulawesi. Active movement of the fault results in high earthquake activity in the region of Central Sulawesi and its surroundings. This makes the importance of earthquake parameters in Central Sulawesi and surrounding areas. One of the efforts to find out earthquake parameter information accurately is to relocate. The purpose of this study was to conduct hypocenter earthquake relocation and determine the 1-D velocity structure of P waves in Central and surrounding areas using the Coupled Velocity - Hypocenter method with Velest 3.3 software. The data used are tectonic earthquake data from November 2009 to March 2018, data recording stations, and initial speed data. The results of data processing using the Velest 3.3 software are that some of the results of the relocation are close to fault, the final Vp at a depth of 9 km is slower than the initial Vp, the correction of the station obtained in this calculation is in the interval -0.81 to +0.54.
In this research, structural engineering of lanthanum-manganate-based material was studied, starting with material synthesizing La0.7(Ca1-xSrx)0.3MnO3 with variation of x=0; 0.1; 0.2; and 0.3 using the sol-gel method as a microwave material. The effects of Sr substitution on the stucture, size of grain, and microwave-absorbing properties were investigated in detail by various analytical methods. Using XRD (X-Ray Diffraction) showed that the sample had single phase and orthorombic structure (space group of Pnma), substitution of Sr2 + ions did not cause changes in structure. Characterized using SEM (Scanning Electron Microscope) showed change in grain size which increase when given Sr substitution. Characterized using VNA (Vector Network Analyzer) in the 8-12 GHz range shows that the sample La0.7(Ca1-xSrx)0.3MnO3 with x=0 has been able to absorb up to 55.64% microwaves at 10.44GHz. The study concluded the material of La0.7(Ca1-xSrx)0.3MnO3 have a good potential to be a candidate of microwave absorbing materials.
Pada penelitian ini dipelajari rekayasa struktur material komposit berbasis neodymium manganit, yang dimulai dengan mensintesis material Nd0,6Sr0,4MnO3 (NSMO) dengan menggunakan metode sol-gel, lalu dilanjutkan dengan sintesis material komposit (Nd0,6Sr0,4MnO3)1-x/(Fe2O3)x (x= 0; 0,3; 0,5 dan 0,7). Sampel dikarakterisasi dengan menggunakan XRD (X-Ray Diffraction) menunjukkan bahwa sampel NSMO memiliki struktur kristal orthorombik dengan space group P n m a, pengkompositan dengan Fe2O3 tidak menyebabkan perubahan struktur tetapi muncul fasa lain yang ditandai dengan adanya puncak difraksi milik Fe2O3. Karakterisasi FESEM (Field Emission Scanning Electron Microscope) menunjukkan persebaran butir yang merata dengan ukuran butir rata-rata 0.186 μm. Karakterisasi VSM (Vibrating Sample Magnetometer) pada temperatur ruang (298 K) dengan medan magnet 5 T, menunjukkan material komposit NSMO / Fe2O3 bersifat paramagnetik dan nilai magnetisasi serta susceptibilitas sampel semakin menurun seiring dengan penambahan konsentrasi Fe2O3.
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