Investigasi Struktur Kristal, Struktur Lokal, Sifat Listrik, dan Kemagnetan pada Material Feroelektrik Berbasis K0,5Na0,5NbO3 (KNN) Didoping

Nuraini, Umi (2019) Investigasi Struktur Kristal, Struktur Lokal, Sifat Listrik, dan Kemagnetan pada Material Feroelektrik Berbasis K0,5Na0,5NbO3 (KNN) Didoping. Doctoral thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Studi struktur kristal, struktur lokal, sifat listrik, dan kemagnetan berbasis material bebas timbal, (K0,5Na0,5)NbO3 (KNN) telah berhasil dilakukan. Material (Ba0,8Ca0,2) TiO3 (BCT), (Ba0,8Sr0,2)TiO3 (BST), dan BiFeO3 (BF) dipilih sebagai dopan dengan metode sintesis yang berbeda dan disubstitusikan ke dalam sistem KNN. Identifikasi fase dan struktur kristal didapatkan dari difraksi sinar-X (XRD) dan dianalisis melalui penghalusan Rietveld, sedangkan struktur lokal dipelajari dengan X-ray Absorption Spectroscopy (XAS) pada Ti dan Fe K-edge yang melibatkan X-ray Absorption Near Edge Spectroscopy (XANES) dan Extended X-ray Absorption Fine Structure (EXAFS). Selain itu, sifat listrik yang mencakup penentuan nilai konduktivitas listrik dan permitivitas relatif dikarakterisasi dengan menggunakan plot Cole-Cole dari impedansi kompleks. Kebergantungan nilai permitivitas sebagai fungsi dari frekuensi dan temperatur diukur pada temperatur kamar hingga 500 ºC dengan rentang frekuensi 0,1 Hz – 3,2 MHz. Kurva histeresis polarisasi listrik (P-E) didapatkan melalui penerapan medan listrik 10 kV/cm dan frekuensi 50 Hz, sedangkan Superconducting Quantum Interface Device (SQUD) digunakan untuk karakterisasi kemagnetan material KNN pada pendopingan BF. Substitusi dopan baik BCT, BST, maupun BF mampu memodifikasi sistem KNN yang awalnya berstruktur ortorombik menjadi tetragonal. Lebih lanjut, pendopingan material BF menunjukkan struktur tetragonal yang berbeda dengan nilai tetragonalitas c/a>1 (elongated) pada variasi dopan rendah dan pada dopan tinggi c/a <1 (flattenned). Analisis struktur lokal menunjukkan bahwa lingkungan oktahedron pada sistem KNN telah merubah bilangan oksidasi dari atom Ti pada material KNNBC(S)T dan Fe pada KNNBF serta menciptakan defek muatan dan oxygen vacancy sebagai netralitas muatan pada sistem tersebut. Perubahan struktur kristal dan kehadiran defek muatan ini akan menciptakan mekanisme polarisasi yang berbeda di dalam sistem KNN, yaitu polarisasi lattice dipole dan defect dipole. Kehadiran defek muatan juga menjadikan material KNN lebih konduktif yang ditandai dengan penurunan nilai energi aktivasi dari 0,357 eV menjadi 0,312 eV pada KNNBCT dan 0,308 eV pada KNNBST pada temperatur rendah. Terkait sifat dielektriknya kehadiran defek muatan ini dapat meningkatkan nilai permitivitas relatif dan polarisasi remanensi pada KNN dari 1,877 μC/cm2 menjadi 2,651 μC/cm2 pada pendopingan BST. Untuk material KNNBF variasi x<0,1 nilai polarisasi remanensinya semakin meningkat seiring penambahan dopan dengan nilai maksimum mencapai 4,019 μC/cm2 pada x=0,1 kemudian turun hingga 0,708 μC/cm2 pada x=0,175. Secara umum, karakteristik material KNN berubah dari tipikal feroelektrik menjadi relaksor dengan substitusi dopan, baik BCT, BST, ataupun BF. Pada kemagnetan keseluruhan material KNNBF bersifat feromagnetik pada temperatur kamar dengan nilai magnetisasi saturasi mengalami kenaikan seiring penambahan dopan dan mencapai daerah maksimum pada x=0,075-0,1 akibat kehadiran oxygen vacancy dan turun pada variasi x>0,1 akibat netralitas dari interaksi defek.
Kata kunci: KNN, doping, struktur kristal, struktur lokal, konduktivitas, dielektrik, feroelektrik, magnetik.
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Study of the crystal structure, local structure, electrical, and magnetic properties based on lead-free (K0.5Na0.5)NbO3 (KNN) material had been successfully carried out. (Ba0,8Ca0,2)TiO3 (BCT), (Ba0,8Sr0,2)TiO3 (BST), and BiFeO3 (BF) materials were selected as dopants through different synthesized methods and substituted into the KNN systems. The identification of phase and crystal structure was revealed by X-Ray diffraction (XRD) and analyzed through Rietveld refinements, while the local structure was studied by X-ray absorption spectroscopy (XAS) of Ti and Fe K-edge involving X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Furthermore, electrical properties, include the determination of conductivity and relative permittivity values were characterized by using Cole-Cole plot of complex impedance. The dependence of permittivity as a function of frequency and temperature is measured at room temperature until 500ºC with frequency range of 0,1 Hz-3,2 MHz. The electric polarization (P-E) hysteresis was conducted through the application of electric field at 10 kV/cm and a frequency of 50 Hz, while a superconducting quantum interference device (SQUD) was utilized for magnetization characterization, only for BF doped KNN compositions. The substitution of dopants, with BCT, BST, or BF, was successfully modified KNN system which initially orthorhombic symmetry to tetragonal symmetry. Furthermore, BF doped showed two kinds of tetragonal symmetry, on low dopant had tetragonality values of c/a>1 (elongated structure) and on high dopant had tetragonality values of c/a<1 (flattened structure). The analyzation of local structure showed that the octahedron environment on the KNN system had change the oxidation number of Ti from KNNBC(S)T materials and Fe from KNNBF materials then created charge defect and oxygen vacancy as neutrality in these systems. The change of crystal structure and charge defect will produce the different polarization mechanism on KNN systems, lattice dipole and defect dipole. The presence of charge defect and oxygen vacancy modified KNN became more conductive indicated by decreasing on the activation energy from 0,357 eV to 0,312 eV on KNNBCT, and 0,308 eV on KNNBST at low temperature. Related to dielectric properties, the existence of charge defect increased the value of relative permittivity and remnant polarization on KNN material from 1,877 μC/cm2 to 2,651 μC/cm2 on BST doped. On KNNBF materials with variation x<0,1 its remnant polarization increased and had maximum value of 4,019 μC/cm2 then decreased with value of 0,708 μC/cm2 on x=0,175. Generally, the characterization of KNN system changed from ferroelectric typical became relaxor typical by substituting of dopant, BCT, BST, or BF. On the magnetism, all of KNNBF materials had a ferromagnetic behavior at room temperature which the saturation magnetization rose as increasing BF doped and reached maximum region on x=0,075-0,1 due to the presence of oxygen vacancy then decreased at variation x>0,1 because of the neutrality from the defect interaction.

Keywords: KNN, doping, crystal structure, local structure, conductivity, dielectric, ferroelectric, magnetic.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	: KNN, doping, crystal structure, local structure, conductivity, dielectric, feroelectric, magnetic
Subjects:	Q Science > QC Physics > QC271 Temperature measurements Q Science > QC Physics > QC610.3 Electric conductivity Q Science > QC Physics > QC 611.97.T46 Temperature effects. Including transition temperature Q Science > QC Physics > QC765 Magnetic materials
Divisions:	Faculty of Natural Science > Physics > 45001-(S3) PhD Thesis
Depositing User:	UMI NURAINI
Date Deposited:	20 Jul 2026 04:53
Last Modified:	20 Jul 2026 04:53
URI:	http://repository.its.ac.id/id/eprint/70487

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