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"ABSTRAKTesis ini melaporkan proses dan hasil penelitian yang dilengkapi oleh karakterisasi materialLa0,67Sr0,33Mn1-xNixO3 dengan variasi x = 0,00 ; 0,15 ; 0,20 ; 0,25 yang telah berhasildisintesis dengan metode sol gel. Hasil refinement dari data XRD menunjukkan bahwa padamaterial La0,67Sr0,33Mn1-xNixO3 telah terbentuk fasa tunggal untuk empat variasi sampel yaituLa0,67Sr0,33Mn1-xNixO3 dengan x = 0,00 ; 0,15 ; 0,20 ; 0,25. Dari hasil refinementmenggunakan perangkat lunak High Score didapatkan ukuran kristal pada masing ? masingsampel 22,66 nm ; 23,26 nm ; 21,18 nm ; 18,62 nm. Gugus fungsi Mn-O-Mn terbentuk darihasil uji FTIR bervibrasi regangan pada bilangan gelombang sekitar 600 cm-1. Dari hasil ujiSEM Informasi mengenai morfologi sampel La0,67Sr0,33Mn1-xNixO3 menunjukkan bahwaantara partikel saling teraglomerasi. Pada hasil pengujian distribusi ukuran partikelmenunjukkan bahwa rata ? rata ukuran partikel x = 0,00 ; 0,15 ; 0,20 ; 0,25 yaitu 502,9 nm ;447,6 nm ; 264,8 nm ; 371,7 nm. Jumlah konsentrasi spin pada sampel pada masing ? masingnilai x pada hasil uji ESR menunjukkan penurunan, yaitu ketika doping Ni ditambah makaluas area dibawah kurva absorpsi menurun. Hal ini dikarenakan adanya ion Ni2+ yangmensubstitusi ion Mn3+ sehingga menghambat hopping elektron dari elektron eg (ion Mn3+)ke t2g (ion Mn4+) pada mekanisme double excange sehingga spin pada elektron t2g akanantiparalel. Kompetisi antara sifat feromagnetik dengan antiferomagnetik menjadikan spinakan berubah arah sehingga kemagnetan sampel akan menurun dan momen magnetikmenjadi acak. Hasil ESR ini digunakan untuk mengkonfirmasi hasil VNA. Kemampuanabsorpsi gelombang mikro ditunjukkan dengan nilai reflection loss pada sampel x = 0,00 ;0,15 ; 0,20 ; 0,25 berturut-turut sebesar -65,37 dB , -66,17 dB, -66,67 dB dan -77,22 dB.Reflection loss meningkat ketika doping Ni ditambah karena gelombang elektromagnetikyang diberikan kepada sampel La0,67Sr0,33Mn1-xNixO3 digunakan untuk menyearahkan momenmagnetik.

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ABSTRACTThis thesis reports the process and the results are supplemented by material characterizationLa0,67Sr0,33Mn1-xNixO3with variation x = 0.00; 0.15; 0.20; 0.25 which has been synthesized bysol gel method. Results refinement of the XRD data showed that the material La0,67Sr0,33Mn1-xNixO3have formed a single phase to four-sample variation is La0,67Sr0,33Mn1-xNixO3with x =0.00; 0.15; 0.20; 0.25. From the results of using the software refinement High Score obtainedcrystal size on each - each sample of 22.66 nm; 23.26 nm; 21.18 nm; 18.62 nm. Functionalgroups Mn-O-Mn is formed from the FTIR test strain vibrate at wave number 600 cm-1.From the test results SEM morphology Information La0,67Sr0,33Mn1-xNixO3samples showedthat the particles are agglomerated. In the particle size distribution of the test results showedthat the average - average particle size x = 0.00; 0.15; 0.20; 0.25 is 502.9 nm; 447.6 nm;264.8 nm; 371.7 nm. Number of spin concentration in the sample on each - each value of x inthe ESR test results showed a decrease, when doping Ni plus, the area under the curve ofabsorption decreases. This is due to the substitution of Ni2+ ions Mn3+ ions thus inhibitingelectron hopping of electrons eg (ion Mn3+) to t2g (Mn4+ ion) in the mechanism of doubleexcange so that the spin of the electrons will t2g antiparallel. Competition betweenferromagnetic properties with antiferromagnetic spin make will change the direction so thatthe sample magnetization will decrease and the magnetic moments become random. ESRresults are used to confirm the results of the VNA. Microwave absorption ability is indicatedby the value of reflection loss on the sample x = 0.00; 0.15; 0.20; 0.25 respectively for -65.37dB, -66.17 dB, -66.67 dB and -77.22 dB. Reflection loss increases when the doping Ni plusbecause the electromagnetic waves given to the sample La0,67Sr0,33Mn1-xNixO3 used to alignthe magnetic moment"

"Modifikasi permukaan pada semen kalsium fosfat dengan multilapis Ti-Al-Cr dan hidroksiapatit dengan metode sol-gel. Implan gigi berbahan dasar logam paduan titanium Ti-Al-Cr dilapisi hidroksiapatit diketahui masih memiliki kelemahan. Oleh karena itu dilakukan pengembangan dengan modifikasi permukaan dengan multilapis Ti-Al-Cr dan hidroksiapatit pada semen kalsium fosfat untuk aplikasi implan dental. Tujuan: Penelitian ini bertujuan untuk melihat ketebalan multilapis logam paduan Ti-Al-Cr dan hidroksiapatit pada CPC dengan sintesis metode sol-gel. Metode: Analisis ketebalan multilapis dan mikrostruktur logam paduan Ti-Al-Cr dan hidroksiapatit pada CPC dilakukan dengan menggunakan Scanning Electron Microscopy (SEM). Hasil: SEM menunjukkan lapisan logam paduan Ti-Al-Cr pada CPC berhasil dibentuk dengan ketebalan 1µm sedangkan lapisan hidroksiapatit yang terbentuk adalah 10µm. Simpulan: Modifikasi permukaan dengan multilapis Ti-Al-Cr dan hidroksiapatit pada CPC berhasil dilakukan dengan menggunakan metode sol-gel dengan ketebalan bervariasi.

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Implan gigis based on metal still has weaknesses. New development is currently developed with the surface modification of multilayer coatings Ti-Al-Cr and hydroxyapatite on calcium phosphate cement (CPC) for Implan gigi application. Objective: To analize the thickness of multilayer coating alloy Ti-Al-Cr and hydroxyapatite on CPC synthesis by sol-gel method. Methods: Scanning electron microscopy (SEM) was conducted to analyze the thickness and morphology of microstructure layer formed on CPC. Result: SEM showed that coating Ti-Al-Cr on CPC successfully formed 1µm of thickness and showed 10µm of hydroxyapatite. Conclusion: The innovation of modification surface multilayer coatings Ti-Al-Cr and hydroxyapatite on CPC was successfully done by sol-gel method with a variety thickness."

"Telah dilakukan penelitian sifat listrik, sifat magnet, dan efek magnetoresistan bahan perovskite manganites La0,67Sr0,33Mn1-XNixO3. Sampel dibuat dengan metode sol gel. Hasil karakterisasi XRD menunjukkan bahwa sampel sudah memiliki fase tunggal dengan struktur rhombohedral dan space group R-3c. Pemberian doping Ni tidak mengubah struktur kristal namun menurunkan nilai parameter kisi kristal. Karakterisasi SEM-EDX menunjukkan bahwa unsur Ni sudah masuk ke dalam sampel dan adanya perubahan morfologi sampel ketika doping Ni divariasikan. Data resistivitas sebagai fungsi temperatur menunjukkan bahwa doping Ni meningkatkan besar resistivitas bahan dan menggeser temperatur transisi metal-isolator ke temperatur yang lebih rendah. Efek magnetoresistan yang diberikan menunjukkan adanya peningkatan persen magnetoresistan saat doping Ni dinaikkan. Sedangkan kurva histerisis yang dihasilkan menunjukkan bahwa pemberian doping Ni menurunkan sifat kemagnetan bahan yang ditunjukkan oleh penurunan magnetisasi bahan.

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The electrical properties, magnetic properties, and magnetoresistance effect of perovskite manganites La0,67Sr0,33Mn1-XNixO3 material have been studied. Samples were synthesized by using sol gel method. The result of XRD characterization showed that samples were single phase with Rhombohedral structure and R-3c space group. Ni doped did not change crystal structure but decreased lattice parameter. SEM-EDX characterization showed that Ni was included in the samples as a doping and the morphology of samples changed with various Ni doped.

Resistivity as temperature function showed that Ni doped increased the resistivity and decreased the metal-insulator transition temperature. Magnetoresistance effect of samples relatively enhanced with increased of Ni doping. While the hysteresis curve from VSM characterization showed that Ni doped decreased magnetic properties of samples."

"Pada penelitian ini dibuat lapisan tipis LaMnO3 menggunakan metode deposisi elektroforesis pada susbtrat stainless steel SS-316 ukuran 1 x 10 x 30 mm. Serbuk LaMnO3 disintesis memakai metode sol-gel dengan campuran stokiometri antara La(NO3)3.6H2O dan Mn(NO3)2.4H2O. Sebagai larutan suspensi dipakai campuran ethanol dan deionized water dengan komposisi 90 : 10 serta serbuk LaMnO3 sebesar 30 mg dalam 50 ml larutan. Dengan memberikan tegangan DC (direct current) sebesar 60 V dan waktu deposisi 15 menit, dapat menghasilkan lapisan tipis dengan permukaan yang homogen yang ditunjukkan dengan nilai root mean square (RMS) roughness sebesar 30,96 nm. Karakterisasi menggunakan X-ray diffractometer (XRD) menunjukkan bahwa sampel lapisan tipis menghasilkan fasa senyawa substrat dan LaMnO3 dengan volume sel dan ukuran kristal meningkat dengan meningkatnya temperatur anil. Hasil scanning electron microscope (SEM) memperlihatkan bahwa morfologi sampel lapisan tipis memperlihatkan ukuran grain berkisar antara 200-400 nm. Karakterisasi dengan fourier transform infra red (FTIR) memperlihatkan bahwa material memiliki pita serapan pada 580 cm-1, merupakan karakteristik absorbsi ikatan Mn-O (streaching Mn-O-Mn pada oktahedral MnO6) yang berhubungan dengan gerakan internal perubahan panjang dari batas Mn-O-Mn. Hasil karakterisasi dengan vibration sample magnetometer (VSM) menunjukkan bahwa lapisan tipis LaMnO3 memiliki sifat feromagnetik. Kurva histerisis yang dihasilkan menunjukkan bahwa kenaikan temperatur anil menyebabkan meningkatnya sifat kemagnetan bahan. Nilai magnetisasi saturasi Ms sebesar 2,377 emu/g dan koersivitas Hc sebesar 212,03 Oe dicapai ketika temperatur anil 950°C. Hasil proses deposisi selama 15, 25 dan 35 menit, didapatkan hasil bahwa lapisan tipis LaMnO3 dapat digunakan sebagai bahan penyerap gelombang mikro. Bahan ini memiliki nilai permitivitas dan permeabilitas yang relatif tinggi dengan empat puncak serapan pada range frekuensi 8 – 12 GHz. Nilai reflection loss paling besar dalam tanda negatif dicapai oleh sampel dengan waktu deposisi 15 menit serta suhu anil 900°C sebesar - 49,25 dB pada frekuensi 8,59 GHz dan bandwidth sebesar 0,86 GHz. Sampel ini memiliki impedansi (Zin=33,3-j37,3 Ω) mendekati nilai impedansi line transmisition Zo (50 Ω)

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In this study, a thin layer of LaMnO3 was prepared using the electrophoretic deposition method on a 1 x 10 x 30 mm stainless steel SS-316 substrate. LaMnO3 powder was synthesized using the sol-gel method with a stoichiometric mixture of La(NO3)3.6H2O and Mn(NO3)2.4H2O. As a suspension solution used a mixture of ethanol and deionized water with a composition of 90 : 10 and LaMnO3 powder of 30 mg in 50 ml of solution. By providing a DC (direct current) voltage of 60 V and a deposition time of 15 minutes, it can produce a thin layer with a homogeneous surface as indicated by the root mean square (RMS) roughness value of 30.96 nm. Characterization using an X-ray diffractometer (XRD) showed that the thin layer samples produced a substrate and LaMnO3 compound phase with cell volume and crystalline size increasing with increasing annealing temperature. Scanning electron microscope (SEM) results show that the morphology of the thin layer samples shows grain sizes ranging from 200-400 nm. Characterization with Fourier transform infrared (FTIR) produces an absorption band of about 580 cm-1, which is a characteristic of Mn-O bond absorption (Streaching Mn-O-Mn on the MnO6 octahedron) which is related to the internal movement of changes in length from the Mn-O Mn boundary. The results of characterization with a vibration sample magnetometer (VSM) showed that the LaMnO3 thin layer has ferromagnetic properties. From the resulting hysteresis curve, the increase in sintering temperature increases the magnetic properties of the material. The saturation magnetization value of Ms reached 2.377 emu/g and the Hc coercivity of 212.03 Oe was achieved when the annealing temperature was 950°C. The results of the deposition process for 15, 25 and 35 minutes showed that the LaMnO3 thin layer could be used as a microwave absorbent material. This material has relatively high permittivity and permeability values ​​with four absorption peaks in the frequency range of 8 – 12 GHz. The larger the negative value of reflection loss was achieved by samples with a deposition time of 15 minutes and annealing time of 900°C of -49.25 dB at a frequency of 8.59 GHz and a bandwidth of 0.86 GHz. This sample has an impedance (Zin=33.3-j37.3Ω) close to the line transmission impedance value Zo (50Ω)."

"Telah dilakukan penelitian mengenai pengaruh doping nikel terhadap sifat penyerap gelombang mikro pada senyawa La0,67Sr0,33Mn 1-x NixO3 yang disintesis dengan Metode Sol-gel. Karakterisasi XRD menunjukkan bahwa La0,67Sr0,33Mn 1-x NixO3 memiliki fasa tunggal dengan struktur kristal rhombohedral. Dari hasil SEM-EDX terlihat bahwa ukuran partikel cenderung mengecil dan tidak ada unsur lain impuritas pada material. Pengujian dengan menggunakan Cryogenic Magnetometer menunjukan nilai resistivitas terbesar yaitu 1.49 ?m untuk x = 0,3. Hasil karakterisasi VNA menunjukan doping Ni dapat meningkatkan kemampuan penyerapan gelombang mikro. Nilai Reflection Loss terbesar yaitu -11,492 dB untuk x = 0,3<.

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A research on the effect of nickel doping on microwave absorption properties of La0,67Sr0,33Mn1 xNixO3 had been reported. The samples were synthesized by the sol gel method. The XRD characterization shows that La0,67Sr0,33Mn 1 x NixO3 had a single phase with a rhombohedral crystal structure. SEM EDX results show that there is no other element besides main elements and particle size decrease after doping Ni. Cryogenic Magnetometer showed that the resistivity increase after incoporation of Ni, the largest resistivity is 1,49 for x 0,3. The VNA characterization showed that after doping Ni The microwave absorption properties had been significantly improved. The largest Reflection Loss value is 11.49 dB for x 0,3<."

"[ABSTRAKPenggunaan gelombang mikro dalam beberapa tahun terakhir ini mengalami peningkatan yang sangat pesat seiring berkembangnya teknologi komunikasi dan informasi. Hal ini menimbulkan masalah baru yakni terjadinya polusi gelombang mikro. Untuk mengimbangi dampak negatif polusi interferensi gelombang elektromagnetik, para peneliti mencoba mengembangkan material penyerap gelombang elektromagnetik. Salah satu material yang menjadi kandidat potensial untuk aplikasi penyerap gelombang mikro adalah material berbasis lantanum manganat. Pada penelitian ini dipelajari rekayasa struktur material berbasis lantanum manganat dengan sistem La0,67Ba0,33Mn1-xNix/2Tix/2O3 (x = 0; 0,02; 0,04 dan 0,06). Fasa tunggal senyawa La0.67Ba0.33Mn1-xNix/2Tix/2O3 berhasil dibuat melalui proses pemaduan mekanik menggunakan prekusor-prekusor La2O3, MnCO3, BaCO3, TiO2, dan NiO dengan tingkat kemurnian tinggi. Selanjutnya serbuk hasil pemaduan mekanik menjalani perlakuan pemanasan pada suhu 1200oC selama 10 jam. Material yang telah dipanaskan kemudian dihaluskan kembali selama 20 jam. Hasil refinement pola difraksi sinar X menunjukkan bahwa senyawa La0,67Ba0,33Mn1-xNix/2Tix/2O3 memiliki strukstur kristal monoklinik untuk seluruh variasi x. Kurva histerisis sampel menunjukkan bahwa material ini termasuk magnet lunak. Hasil evaluasi distribusi ukuran partikel material dengan komposisi terbaik yakni La0,67Ba0,33Mn0,06Ni0,03Ti0,03O3 adalah 82,4 nm. Hasil pengujian sifat serapan gelombang mikro pada rentang 8-12,4 GHz menunjukkan material mampu mereduksi gelombang mikro hingga 94 % pada frekuensi 11,4 GHz. Dengan demikian senyawa La0,67Ba0,33Mn1-xNix/2Tix/2O3 dapat dijadikan sebagai material penyerap gelombang mikro.;

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ABSTRACTIn recent years, application of microwaves has been increased along with the development of communication and information technology and highly produces electromagnetic wave interference. To solve this problem, scientist tries to develop a new material that could absorb electromagnetic waves. One of potential candidates for absorbing materials is lanthanum manganese-based system. In this research, La0.67Ba0.33Mn1-xNix/2Tix/2O3 (x = 0, 0.02, 0.04, and 0.06) compound were studied as a microwaves absorber materials. Single phase of La0.67Ba0.33Mn1-xNix/2Tix/2O3 were successfully synthesized by mechanical alloying method. The mixture of all precursors were first mechanically milled for 20 hours and then sintered at a temperature of 1200oC for 10 h in which a fully crystalline material is ensured. The sintered materials were then re-milled for 20 hours to obtain powder-based nanoparticle. X-ray diffraction refinement shows that the samples have monoclinic structure at all x compositions. The hysteresis curve evaluation showed that the sample materials is soft magnetic. The best composition of La0.67Ba0.33Mn1-xNix/2Tix/2O3 with x = 0.06 has been evaluated. The compound has 82.4 nm particle size distributions and it is able to absorb up to 94% microwaves at 11.4 GHz. The study concluded the material of La0.67Ba0.33Mn1-xNix/2Tix/2O3 have a good potential to be a candidate of microwaves absorbing materials.;In recent years, application of microwaves has been increased along with the development of communication and information technology and highly produces electromagnetic wave interference. To solve this problem, scientist tries to develop a new material that could absorb electromagnetic waves. One of potential candidates for absorbing materials is lanthanum manganese-based system. In this research, La0.67Ba0.33Mn1-xNix/2Tix/2O3 (x = 0, 0.02, 0.04, and 0.06) compound were studied as a microwaves absorber materials. Single phase of La0.67Ba0.33Mn1-xNix/2Tix/2O3 were successfully synthesized by mechanical alloying method. The mixture of all precursors were first mechanically milled for 20 hours and then sintered at a temperature of 1200oC for 10 h in which a fully crystalline material is ensured. The sintered materials were then re-milled for 20 hours to obtain powder-based nanoparticle. X-ray diffraction refinement shows that the samples have monoclinic structure at all x compositions. The hysteresis curve evaluation showed that the sample materials is soft magnetic. The best composition of La0.67Ba0.33Mn1-xNix/2Tix/2O3 with x = 0.06 has been evaluated. The compound has 82.4 nm particle size distributions and it is able to absorb up to 94% microwaves at 11.4 GHz. The study concluded the material of La0.67Ba0.33Mn1-xNix/2Tix/2O3 have a good potential to be a candidate of microwaves absorbing materials., In recent years, application of microwaves has been increased along with the development of communication and information technology and highly produces electromagnetic wave interference. To solve this problem, scientist tries to develop a new material that could absorb electromagnetic waves. One of potential candidates for absorbing materials is lanthanum manganese-based system. In this research, La0.67Ba0.33Mn1-xNix/2Tix/2O3 (x = 0, 0.02, 0.04, and 0.06) compound were studied as a microwaves absorber materials. Single phase of La0.67Ba0.33Mn1-xNix/2Tix/2O3 were successfully synthesized by mechanical alloying method. The mixture of all precursors were first mechanically milled for 20 hours and then sintered at a temperature of 1200oC for 10 h in which a fully crystalline material is ensured. The sintered materials were then re-milled for 20 hours to obtain powder-based nanoparticle. X-ray diffraction refinement shows that the samples have monoclinic structure at all x compositions. The hysteresis curve evaluation showed that the sample materials is soft magnetic. The best composition of La0.67Ba0.33Mn1-xNix/2Tix/2O3 with x = 0.06 has been evaluated. The compound has 82.4 nm particle size distributions and it is able to absorb up to 94% microwaves at 11.4 GHz. The study concluded the material of La0.67Ba0.33Mn1-xNix/2Tix/2O3 have a good potential to be a candidate of microwaves absorbing materials.]"

"ABSTRAKTujuan: Mengetahui pengaruh gel ekstrak belimbing wuluh terhadap perubahanwarna email gigi. Metode: 30 spesimen gigi sapi dibagi menjadi 6 kelompok, yaitukelompok aplikasi gel ekstrak belimbing wuluh Aceh 70% , 80%, dan 90%, sertaekstrak belimbing wuluh Bogor 70%, 80%, dan 90%. Aplikasi gel dilakukan selama4 jam per hari dalam 14 hari aplikasi. Pengukuran nilai warna dilakukan awal,setelah 7 hari, dan 14 hari aplikasi menggunakan VITA Easyshade® denganperhitungan perubahan warna didapat melalui rumus CIEL*a*b. Hasil: Dari uji tberpasangan, didapatkan terjadi perubahan warna yang bermakna setelah 7 hari dan14 hari aplikasi gel ekstrak belimbing wuluh Aceh dan Bogor konsentrasi 70% dan80%. Kesimpulan: Peningkatan perubahan warna menyebabkan diskolorasipermukaan email setelah aplikasi gel ekstrak belimbing wuluh.

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ABSTRACTObjectives: To investigate the effect of gel containing small starfruit extracts to thecolour change of tooth enamel. Methods: 30 specimens of bovine teeth were dividedinto 6 groups which would be applied with gels with different concentration (withAceh?s small starfruit extracts 70%, 80%, 90%, and Bogor?s small starfruit extracts70%, 80%, 90%). Gel application was done 4 hours per day in 14 days. Themeasurement of the colour change performed before application, 7 days, and 14 daysof application using VITA Easyshade® with calculation of the colour change wasobtained through CIEL*a*b* formula. Results: From dependent t-test, there was asignificant color change after 7 days and 14 days application of gel containing 70%and 80% small starfruit extracts. Conclusion: Increased color changes causesdiscoloration of enamel surface after application of gel starfruit extracts."

"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."

"Telah dilakukan penelitian mengenai sifat penyerapan gelombang mikro material La0.8Ca0.2-xAgxMnO3 x= 0;0,05;0.1;0,15 yang termasuk golongan material perovskit manganat. Material disintesis menggunakan metode sol gel, kemudian dilakukan kalsinasi pada suhu 550?C, dan sintering di suhu 900?C. Karakterisasi XRD menunjukkan bahwa sampel berada dalam fasa tunggal. Dilakukan uji SEM yang menunjukkan morfologi sampel serta EDX yang menampilkan kemurnian sampel. Pengujian menggunakan magnetometer kriogenik menunjukkan penurunan resistivitas bahan. Sampel telah dikonfirmasi ulang menggunakan uji ESR, untuk melihat konsenterasi elektron bebas pada sampel. Terakhir, sampel diuji menggunakan VNA untuk mengetahui Refleksi hilang, permittivitas dan permeabilitas bahan, dengan RL paling tinggi sebesar -4,965 dB.Kata kunci: Perovskit manganat, Sol Gel, Refleksi Hilang, Permitivitas, Permeabilitas.

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The research about microwave absorption property of La0.8Ca0.2 xAgxMnO3 x 0 0.05 0.10 0.15 material is reported. The material synthesized by sol gel method, calcinated at 550 C and sintered at 900 C. According to XRD characterization, all samples were single phase. By SEM characterization the morphology of the samples are reported. EDX confirmed that all the samples have a good compositional purity.

Cryogenic magnetometer reported that Ag dopant caused the resistivity of materials generally decreased. ESR confirmed that Ag dopant also caused concentration of free electrons were increase. Finally VNA characterization reported the Reflection Loss, permittivity, and permeability, which the maximum RL is 4.965 dB."

"Pengaruh doping Ag terhadap sifat listrik dan magnetoresistansi material La0,8 Ca1-xAgx 0,2MnO3 x = 0; 0,05; 0,15; 0,2 telah diinvestigasi. Material La0,8Ca0,2MnO3 merupakan salah satu member dari material perovskite manganite yang mempunyai struktur umum ABO3. Material yang dihasilkan dikarakterisasi menggunakan XRD, SEM, dan Cryogenic Magnetometer. Hasil karakterisasi XRD didapatkan material memiliki fasa tunggal, dengan menggunakan metode pencocokan rietvield diketahui pendopingan Ag sebesar 0 le; x le; 0,05 memilki struktur orthorombik, namun ketika doping Ag sebesar x ge; 0,15 material mengalami transformasi struktur menjadi rhomohedral. Karakterisasi SEM menunjukkan perubahan ukuran rata-rata grain ketika doping silver meningkat. Dari hasil EDX terlihat unsur Ag telah berhasil tersubstitusi kedalam matriks La0,8Ca0,2MnO3 dengan nilai komposisi dari unsur-unsur yang ada didalamnya mendekati nilai komposisi perhitungan. Hasil karakterisasi cryogenic magnetometer menunjukkan pendopingan silver ke dalam ion Ca pada material La0,8Ca0,2MnO3 dapat menurunkan resistivitas bahan dan menaikkan nilai temperatur transisi metal ke isolator TMI , namun pada x = 0,2 resistivitas bahan kembali meningkat yang diikuti penurunan nilai TMI. Persen magnetoresistansi MR menunjukkan peningkatan ketika bahan La0,8Ca0,2MnO3 didoping oleh 5 dan 15 silver pada ion Ca-nya, namun ketika didoping silver sebesar 0,2 persen MR kembali menurun, yang mana MR terbesar yang didapatkan pada penelitian ini adalah 6 dengan komposisi doping x = 0,15.

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The effect of Ag doping on electrical properties and magnetoresistance of La0,8 Ca1 xAgx 0,2MnO3 x 0 0,05 0,15 0,2 materials has been investigated. La0,8Ca0,2MnO3 material is one member of the perovskite manganite material that has a general structure ABO3. Samples that have been synthesized, XRD measurement were taken. After that, the samples are compressed using dice, in which has a diameter 12 mm. So in here, the shape of the samples will be pellet. The pellet samples characterized using SEM EDX and Cryogenic Magnetometer. XRD characterization results obtained, all the samples has a single phase, by using rietvield refinement technique it is known that the substitution of Ag with large doping x ge 0,15 occurs the transformation of structure to rhombohedral. SEM characterization indicates a grain size change when the level of doping Ag increases. The EDX results indicate that the silver elementhas successfully entered into La0,8Ca0,2MnO3 matrix with the composition value of the elements contained therein close to the composition value from the calculation. Cryogenic Magnetometer results show that substitution of Ag into the material La0,8Ca0,2MnO3 , it can decrease the resistivity of the material and increase the value of TMI of the material, but when doping silver was 0,2, The resistivity of material returns increases and TMI value decreases. The Percentage of magnetoresistance MR shown an increase when the La0,8Ca0,2MnO3 material was doped by 5 and 15 silver, but when silver doped 0,2 , percentage of MR decreased again, the largest MR obtained in this study was 6 with doping Ag was 0,15. "