Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-10-10T12:18:35Z No. of bitstreams: 1 brunanadianevesdasilva.pdf: 7267349 bytes, checksum: 105653b8c907fb40f7e88e2da5b3173c (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-10-10T12:23:12Z (GMT) No. of bitstreams: 1 brunanadianevesdasilva.pdf: 7267349 bytes, checksum: 105653b8c907fb40f7e88e2da5b3173c (MD5) / Made available in DSpace on 2017-10-10T12:23:12Z (GMT). No. of bitstreams: 1 brunanadianevesdasilva.pdf: 7267349 bytes, checksum: 105653b8c907fb40f7e88e2da5b3173c (MD5) Previous issue date: 2017-07-28 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nióbio está entre os metais de alta importância tecnológica e o Brasil tem a maior reserva, produção global e do comércio nessa área. As perovskitas (ABO3), tais como o PZT, exibem propriedades ferroelétricas e piezoelétricas, importantes no setor eletrônico. Por questões ambientais busca-se por materiais livres de chumbo e o niobato de sódio (NaNbO3) é um bom candidato nesse caso, pois também possui uma série de fases em função da temperatura. Porém, esse polimorfismo ainda é pouco compreendido experimentalmente e cálculos DFT podem ser uma boa ferramenta de auxílio para estudo estrutural. Portanto, foi dado como objetivo do trabalho investigar fases do NaNbO3, comparando resultados teóricos e experimentais. O NaNbO3 foi sintetizado pelo Nb2O5 e tratado termicamente para caracterizações por TG-DTA, RMNES de 23Na e DRX. Modelos teóricos foram elucidados a partir de dados da literatura e todos os cálculos ab initio usando DFT se procederam com o pacote de programa QUANTUM ESPRESSO. As otimizações de geometria tiveram boa concordância com os parâmetros da literatura. A análise térmica confirmou formação do niobato. Após tratamento térmico, foram comparados picos de difrações de raios X das amostras com as simulações dos modelos otimizados. As análises de RMNES do núcleo de 23Na mostrou distinção entre os sítios químicos nas amostras pela convolução de sinais quadrupolares obtidos no cálculo, servindo, portanto, como uma sonda para o estudo desse polimorfismo. Além disso, os parâmetros de RMNES calculados dos núcleos de 93Nb identificou as distorções estruturais de cada fase. Ambas as técnicas concluíram que as amostras B1 e C1 sugeriram ser da fase S; D2 entre a R e a S; D1 entre as fases P e R. Pela estrutura de bandas, houve decaimento de gap para a sequência das fases. Cálculos de pDOS e cargas de Bader indicaram que essas propriedades eletrônicas não foram alteradas pelas diferenças estruturais entre os modelos. O cálculo de fônons identificou uma frequência imaginária na fase cúbica e foi proposto modificações dentro da célula unitária. Os espectros de IV das fases mostraram acoplamentos específicos de modos vibracionais, cuja diferenças entre elas se deve às distorções estruturais. A análise termodinâmica concluiu que a fase B possuía o maior valor de energia total, porém, pelas variações energéticas de menos de 2 kcal/mol, não havia como predizer pela DFT qual delas era a mais estável. / Niobium is among the metals for high technological importance and Brazil has the largest reserve, global production and trade in this area. The perovskites (ABO3), such as PZT, exhibits ferroelectric and piezoelectric properties, important to electronic setor. For environmental reasons, lead-free ceramics are used and sodium niobate (NaNbO3) is good candidate in this case, which also has a series of phases as a function of temperature. However, this polymorphism is still little known experimentally and DFT calculations can be a good tool for the structural study. Therefore, the goal of this work was to investigate phases of the NaNbO3, comparing theoretical and experimental results. Sodium niobate was synthesized by Nb2O5, and thermally treated for their characterizations by TG-DTA, solid-state NMR 23Na nuclei and Xray diffraction. Theoretical models were building from literature datas and all the ab initio calculations using DFT were done with program package QUANTUM ESPRESSO. The geometry’s optimizations had good agreement with the parameters of literature. The thermal analysis confirmed the formation of the niobate. After thermal treatment, the peaks of X-ray diffraction were compared with the simulations of the optimized models. The solidstate NMR analysis of the 23Na nuclei showed distinction between chemical sites at the samples according to the convolution of quadrupole signals obtained by calculations, thus serving as a probe for identification of polymorphism. In addition, the NMR parameters calculated of 93Nb nuclei identified the structural distortions of each phases. The both techniques concluded that the B1 and C1 samples suggested to be of S phase; D2 was between R and S; D1 was an intermediate of the P and R phases. By the band’s structure, there was a decreasing of gap for the sequence of phases. Bader charge analysis and pDOS calculations indicated that these electronic properties were not altered by structural differences between the models. The phonon calculations identified an imaginary frequency in the cubic phase and modifications was proposed inside the unit cell. The IR spectra of the phases showed specified couplings of vibrational modes, whose the differences between them are due to structural distortions. The thermodynamic analysis conclude that B phase had the highest total energy value, however, by the variations of energy less than 2 kcal.mol-1 there was no way to predict by DFT which one was the most stable.

Ferroelectrics are a group of advanced electronic materialswith a wide variety of properties useful in applications suchas memory devices, resonators and filters, infrared sensors,microelectromechanical systems, and optical waveguides andmodulators. Among the oxide perovskite-structured ferroelectricthin film materials sodium potassium niobate or Na0.5K0.5NbO3(NKN) has recently emerged as one of the most promisingmaterials in microwave applications due to high dielectrictunability and low dielectric loss. This licentiate thesispresents results on growth and structural, optical, andelectrical characterization of Na0.5K0.5NbO3 thin films. Thefilms were deposited by rf-magnetron sputtering of astoichiometric, high density, ceramic Na0.5K0.5NbO3 target ontosingle crystal LaAlO3 and Al2O3, and polycrystalline Pt80Ir20substrates. By x-ray diffractometry, NKN films on c-axisoriented LaAlO3 substrates were found to grow epitaxially,whereas films on hexagonal sapphire and polycrystallinePt80Ir20 substrates were found to be preferentially (00l)oriented. Optical and waveguiding properties of theNa0.5K0.5NbO3/Al2O3 heterostructure were characterized using aprism-coupling technique. Sharp and distinguishable transversemagnetic (TM) and electric (TE) propagation modes wereobserved. The extraordinary and ordinary refractive indiceswere calculated to ne = 2.216±0.003 and no =2.247±0.002 for a 2.0 μm thick film at λ = 632.8nm. This implies a birefringence Δn = ne - no =-0.031±0.003 in the film. The ferroelectric state inNKN/Pt80Ir20 films at room temperature was indicated by apolarization loop with polarization as high as 33.4 μC/cm2at 700 kV/cm, remnant polarization of 9.9 μC/cm2 andcoercive field of 91 kV/cm. Current-voltage characteristics ofvertical Au/NKN/Pt80Ir20 capacitive cells and planar Au/NKN/LaAlO3 interdigital capacitors (IDCs) showed very goodinsulating properties, with the leakage current density for anNKN IDC on the order of 30 nA/cm2 at 400 kV/cm. Rf dielectricspectroscopy demonstrated low loss, low frequency dispersion,and high voltage tunability. At 1 MHz NKN/LaAlO3 showed adissipation factor tan δ of 0.010 and a tunability of 16.5% at 200 kV/cm. For the same structure the frequencydispersion, Δεr, between 1 kHz and 1 MHz was 8.5%. <b>Key words:</b>ferroelectrics, sodium potassium niobates,thin films, rf-magnetron sputtering, waveguiding, refractiveindex, prism coupling, dielectric tunability / NR 20140805

L'objectif de ce travail était l'élaboration par ablation laser pulsé (PLD) et la caractérisation de couches minces d'oxydes dans le système K-Nb-O, et plus précisément d'une phase de structure bronze de tungstène quadratique (TTB) sous forme de nanorods, potentiellement intéressante dans le contexte de la recherche de nouveaux piézoélectriques sans plomb. Malgré une forte compétition de croissance entre les différentes phases, l'étude approfondie des conditions de dépôt a montré la possibilité d'obtenir les phases KNb3O8, K4Nb6O17, K6Nb10,88O30 (TTB) et KNbO3, en films minces après une phase d’optimisation essentielle. Nous avons déterminé l'influence des conditions de dépôt sur la formation et la nanostructuration de ces composés en couches minces. En particulier, il a été démontré que la température et la composition de la cible PLD avaient une forte influence sur la croissance de la phase de structure TTB. Une étude plus approfondie de ces phases a révélé que toutes avaient une morphologie spécifique liée à leur structure anisotrope, que nous avons pu contrôler par la croissance épitaxiale sur les substrats SrTiO3 orienté (100) et (110). L'existence d'une activité piézoélectrique dans des couches minces de la phase TTB, mise en évidence par PFM, lui confère un intérêt certain. Cette phase TTB a également été obtenue dans le système Na-K-Nb-O, très connu pour ses propriétés piézoélectriques et ferroélectriques, ouvrant la voie sur de nouvelles recherches. / The purpose of this work was the elaboration by pulsed laser deposition (PLD) and the characterization of thin films of oxides in the K-Nb-O system, and more precisely that of a tetragonal tungsten bronze phase (TTB) as nanorods, of potential interest as a new lead free piezoelectric. In spite of a strong growth competition between the different phases, the detailed study of the deposition conditions showed that it is possible to obtain KNb3O8, K4Nb6O17, K6Nb10,88O30 (TTB ) and KNbO3 in thin films form after an important optimization step. We have determined the influence of these deposition conditions on the formation and the nanostructuration of these compounds as thin films. In particular, it was shown that the temperature and the PLD target’s composition has a strong influence on the growth of the TTB structure. A further study of these phases revealed that all have a specific morphology related to their anisotropic structure, that we have controlled by the epitaxial growth on the (100) and (110) SrTiO3 substrates. The existence of a piezoelectric activity in the TTB thin films, evidenced by PFM, gives a great interest to this phase. This TTB phase was also obtained in the Na-K-Nb-O system, well known for its piezoelectric and ferroelectric properties, opening the way to new research.

O estudo apresentado nesta Tese diz respeito à química dos niobatos lamelares e aborda a síntese, caracterização, avaliação da reatividade intracristalina e das propriedades luminescentes desses materiais. Os niobatos lamelares utilizados foram o hexaniobato K4Nb6O17, o triniobato KNb3O8 e as perovskitas lamelares K1-xLnxCa2-xNb3O10 (Ln = La, Eu e x = 0,02; 0,25; 0,50; 0,75 e 1,00). Esses materiais são constituídos de lamelas que apresentam cargas negativas e a região interlamelar é preenchida por íons de potássio que mantêm a neutralidade dos sistemas. A reatividade intracristalina dos niobatos lamelares foi avaliada frente à intercalação de espécies simples como a butilamina e volumosas como o macrociclo porfirínico, o polioxocátion de alumínio e compostos orgânicos de silício. A alta densidade de carga lamelar dos niobatos lamelares dificulta a intercalação direta de espécies volumosas, o que fez com que novas rotas sintéticas fossem desenvolvidas a fim de permitir a imobilização de tais espécies na região interlamelar. As metodologias sintéticas desenvolvidas foram baseadas, principalmente, no uso de dispersões coloidais dos niobatos esfoliados que, a partir da reestruturação na presença da espécie convidada de interesse, tornou possível a intercalação de espécies volumosas. As propriedades luminescentes dos niobatos lamelares são extremamente dependentes da estrutura do material. Os niobatos com estrutura tipo perovskita não apresentam emissão enquanto que o hexaniobato apresenta emissão apenas a 77 K e o triniobato, à temperatura ambiente. Neste estudo foram avaliadas as propriedades luminescentes dos niobatos EuxK4-3xNb6O17, EuxK1-3xNb3O8 e KCa2Nb3O10 (intercalado com Eu3+ e dopado com 1 % de Eu3+ ou La3+). Foram observados processos de transferência de energia tanto nos niobatos intercalados com Eu3+ quanto nos dopados. A dopagem também provocou mudanças nas propriedades fotofísicas dos niobatos com estrutura perovskita, os quais passaram a apresentar emissão da matriz de niobato mesmo à temperatura ambiente. / The study described in this Thesis is related to the synthesis and evaluation of some chemical properties of layered niobates with formulas K4Nb6O17 (hexaniobate), KNb3O8 (triniobate) and K1-xLnxCa2-xNb3O10 (layered perovskites - Ln = La, Eu and x = 0.02; 0.25; 0.50; 0.75 and 1.00). These niobates are constituted of negative layers and an interlayer region filled with potassium ions that maintain the system charge neutrality. The reactivity of these niobates was evaluated through intercalation reactions of simple species such as butylamine and bulky species such as porphyrin, aluminum polyoxocation and organosilanes. The high charge density of the niobate layer makes the direct intercalation of bulky guest species more difficult. Therefore, to overcome this situation, new synthetic routes were developed. The intercalation of bulky species was achieved by using colloidal dispersions of exfoliated niobates that, upon restaking, incorporate the guest species into the interlayer region. The luminescent properties of the lamellar niobates are very dependent on the structure. Niobates that present a perovskite structure do not show emission even at liquid helium temperature. The hexaniobate presents emission at nitrogen liquid temperature and triniobate at both room and 77 K temperatures. In this study the luminescent properties of EuxK4-3xNb6O17, EuxK1-3xNb3O8 e KCa2Nb3O10 (intercalated with Eu3+ and doped with 1 % of Eu3+ or La3+) were evaluated. Charge transfers processes were observed in both intercalated and doped niobates with Eu3+ ion. The lanthanide doping also promoted changes in the photophysical properties of niobates with perovskite structure, which become to show emission of the niobate group even at room temperature.

O estudo apresentado nesta Tese diz respeito à química dos niobatos lamelares e aborda a síntese, caracterização, avaliação da reatividade intracristalina e das propriedades luminescentes desses materiais. Os niobatos lamelares utilizados foram o hexaniobato K4Nb6O17, o triniobato KNb3O8 e as perovskitas lamelares K1-xLnxCa2-xNb3O10 (Ln = La, Eu e x = 0,02; 0,25; 0,50; 0,75 e 1,00). Esses materiais são constituídos de lamelas que apresentam cargas negativas e a região interlamelar é preenchida por íons de potássio que mantêm a neutralidade dos sistemas. A reatividade intracristalina dos niobatos lamelares foi avaliada frente à intercalação de espécies simples como a butilamina e volumosas como o macrociclo porfirínico, o polioxocátion de alumínio e compostos orgânicos de silício. A alta densidade de carga lamelar dos niobatos lamelares dificulta a intercalação direta de espécies volumosas, o que fez com que novas rotas sintéticas fossem desenvolvidas a fim de permitir a imobilização de tais espécies na região interlamelar. As metodologias sintéticas desenvolvidas foram baseadas, principalmente, no uso de dispersões coloidais dos niobatos esfoliados que, a partir da reestruturação na presença da espécie convidada de interesse, tornou possível a intercalação de espécies volumosas. As propriedades luminescentes dos niobatos lamelares são extremamente dependentes da estrutura do material. Os niobatos com estrutura tipo perovskita não apresentam emissão enquanto que o hexaniobato apresenta emissão apenas a 77 K e o triniobato, à temperatura ambiente. Neste estudo foram avaliadas as propriedades luminescentes dos niobatos EuxK4-3xNb6O17, EuxK1-3xNb3O8 e KCa2Nb3O10 (intercalado com Eu3+ e dopado com 1 % de Eu3+ ou La3+). Foram observados processos de transferência de energia tanto nos niobatos intercalados com Eu3+ quanto nos dopados. A dopagem também provocou mudanças nas propriedades fotofísicas dos niobatos com estrutura perovskita, os quais passaram a apresentar emissão da matriz de niobato mesmo à temperatura ambiente. / The study described in this Thesis is related to the synthesis and evaluation of some chemical properties of layered niobates with formulas K4Nb6O17 (hexaniobate), KNb3O8 (triniobate) and K1-xLnxCa2-xNb3O10 (layered perovskites - Ln = La, Eu and x = 0.02; 0.25; 0.50; 0.75 and 1.00). These niobates are constituted of negative layers and an interlayer region filled with potassium ions that maintain the system charge neutrality. The reactivity of these niobates was evaluated through intercalation reactions of simple species such as butylamine and bulky species such as porphyrin, aluminum polyoxocation and organosilanes. The high charge density of the niobate layer makes the direct intercalation of bulky guest species more difficult. Therefore, to overcome this situation, new synthetic routes were developed. The intercalation of bulky species was achieved by using colloidal dispersions of exfoliated niobates that, upon restaking, incorporate the guest species into the interlayer region. The luminescent properties of the lamellar niobates are very dependent on the structure. Niobates that present a perovskite structure do not show emission even at liquid helium temperature. The hexaniobate presents emission at nitrogen liquid temperature and triniobate at both room and 77 K temperatures. In this study the luminescent properties of EuxK4-3xNb6O17, EuxK1-3xNb3O8 e KCa2Nb3O10 (intercalated with Eu3+ and doped with 1 % of Eu3+ or La3+) were evaluated. Charge transfers processes were observed in both intercalated and doped niobates with Eu3+ ion. The lanthanide doping also promoted changes in the photophysical properties of niobates with perovskite structure, which become to show emission of the niobate group even at room temperature.

Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, and electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies. Ferroelectric materials usually have high dielectric constants, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used in fabrication capacitors for electronic industry because of their high dielectric constants, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure, and electrically tunable microwave integrated circuits using ferroelectric thin films can be developed. Therefore, it is very important to characterize the dielectric constant and tunability of ferroelectric thin films. This thesis shows experimental results for growth, crystalline properties and microwave characterization of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering of a stoichiometric, high density, ceramic NKN, ATN, BST target onto single crystal LaAlO3(LAO), Al2O3 (sapphire), and Nd:YAlO3, and amorphous glass substrates. By x-ray diffractometry, NKN, ATN, BST films on LAO substrates were found to grow epitaxially, whereas films on r-cut sapphire substrates were found to be preferentially (00l) oriented. Coplanar waveguide interdigital capacitor (CPWIDC) structures were fabricated by standard photolithography processing and metal lift-off technique. Microwave properties of the NKN/Sapphire and ATN/Sapphire with CPW structures were characterized using on-wafer microwave measurement technique. Measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field through the connection between network analyzer and power supply was applied to measure voltage tunability. Measured S-parameter were used for the calculation of capacitance, loss tanδ, tunability and K-factor. The NKN films interdigital capacitors with 2 μm finger gap on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor = tunability/tanδ from 152% @ 10GHz to 46% @ 40GHz. The microwave performance of ATN film CPWIDC with 2 μm finger gap on sapphire substrate in the microwave range from 1 to 40 GHz showed that frequency dispersion is about 4.3%, voltage tunability was 4.7% @ 20GHz and 200 kV/cm, loss tangent ∼ 0.068 @ 20GHz, K-factor = tunability/tanδ is ranged from 124% @ 10GHz to 35% @ 40GHz. The BST films CPWIDC with 2μmfinger gap on Al2O3 substrate showed frequency dispersion of capacitance in the microwave range from 1 to 40 GHz about 17%, voltage tunability = 1 - C(40V)/C(0) ∼ 22.2%, loss tangent ∼ 0.137 @ 20GHz, and K-factor = tunability/tanδ from 281% @ 10GHz to 95% @ 40GHz. / QC 20101207

Neste trabalho, foram sintetizados complexos de cobre e ferro, com ligantes imínicos, obtidos a partir de 2-acetilpiridina e 2-(2-aminoetilpiridina) (apyepy), ou 2-acetilpiridina e 2-(aminometil)benzimidazol (apyambi), e com ligantes comerciais (ácido nitrilotriacético ou picolínico), capazes de catalisar a oxidação de poluentes, como benzeno, tolueno, etilbenzeno e xilenos (BTEX). Foi utilizado o tolueno como composto-modelo destes poluentes, que foi degradado com o uso de peróxido de hidrogênio, persulfato de sódio, ácido peracético ou peróxidos de metais alcalinos como agentes oxidantes. Os ligantes imínicos foram obtidos a partir de precursores carbonílicos e amínicos adequados, através de reações de condensação, e os correspondentes complexos metálicos de cobre(II), ferro(II) ou ferro(III) foram isolados utilizando métodos usuais de nosso laboratório. A caracterização dos compostos foi feita através de diversas técnicas analíticas e espectroscópicas: UV/Vis, infravermelho (IV) e de ressonância paramagnética eletrônica (EPR). Posteriormente, foi feita a inserção desses complexos de ferro e de cobre sintetizados em matrizes inorgânicas de niobatos e a verificação de sua reatividade em comparação com as mesmas espécies em solução. Monitorou-se a degradação do tolueno pelo peróxido de hidrogênio por cromatografia gasosa e os resultados obtidos indicaram boa atividade catalítica dos complexos, tanto em solução como inseridos em matrizes de niobato. Em solução, os complexos imínicos foram mais ativos que os de ligantes comerciais. Os compostos de ferro com ambos os ligantes imínicos mostraram-se melhores catalisadores que os correspondentes de cobre e um dos ligantes testados foi o mais eficiente (apyepy) com ambos os metais. A inserção em niobatos, aparentemente, preserva o catalisador e mantém sua atividade por mais tempo, mostrando que a inserção em niobatos beneficia o processo / In this work, iron and copper complexes were synthesized, with imine ligands obtained from 2-acetylpyridine and 2-(2-aminethylpiridine) (apyepy), or 2- acetylpyridine and 2- (aminomethyl)benzimidazole (apyambi) and commercial ligands (nitriletriacetic and picolinic acids) that are able to catalyze the oxidation of pollutant compounds as benzene, , ethylbenzene and xilenes (BTEX). Toluene was used as model compound of those pollutants, and its degradation was verified by using hydrogen peroxide, alkaline peroxide, sodium persulfate, or peracetic acid as oxidant agent. The imine ligands were obtained from adequate carbonyl and amine precursors, in condensation reactions, and the corresponding copper(II), iron(II) and iron(III) complexes were isolated by usual methods developed in our laboratory. Their characterization was carried out by analytical and spectroscopic techniques (UV/Vis, IR and EPR). Those complexes were then inserted in inorganic matrices (niobates) e its reactivity were compared to that of the analogous species in solution. Toluene degradation by hydrogen peroxide was monitored by gas chromatography, and the results showed good catalytic activity of all the complexes, both in solution and inserted into niobate matrices. In solution, the imine complexes were more efficient than the species with commercial ligands. The iron compounds with both imine ligands acted as better catalysts than the corresponding copper species, and for both metals those with the ligand apyepy were the most efficient in both cases. The insertion in niobates apparently preserves the catalyst and maintains its activity for longer, attesting that the insertion ameliorated the process.

Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies. Ferroelectric materials usually have high dielectric constant, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used to fabricate capacitors for electronic industry because of their high dielectric constant, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure and used for electrically tunable microwave integrated circuits. It is an important task to sinter highly tunable and low loss ferroelectrics, fabricate and test the properties of microwave ferroelectric components. This thesis shows experimental results on growth, crystalline and microwave properties of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), and AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering techniques from stoichiometric high density ceramic NKN, ATN, ATO, ANO and BST targets onto LaAlO3 (LAO), Al2O3 (r-cut sapphire), Nd:YAlO3 single crystals and amorphous glass substrates. Advanced X-ray diffraction examinations showed NKN, ATN, BST films on LAO substrates grow epitaxially, whereas films on r-cut sapphire were found to be preferentially (00l) oriented. Coplanar waveguide 2 µm finger gap interdigital capacitor (CPWIDC) structures were fabricated by photolithography process and metal lift-off technique. On-wafer tests up to 40 GHz were performed to characterize microwave properties of the ferromagnetic film CPWIDC devices. The measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field was applied to planar capacitors to measure tunability. Original de-embedding technique has been developed to calculate capacitance, loss tan δ, and tunability of varactors from the measured S-parameters. NKN film interdigital capacitors on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ~ 0.13, K-factor = tunability/tan δ from 152% @ 10GHz to 46% @ 40GHz. The ATN/sapphire CPWIDCs showed the lowest dispersion ~ 4.3% in whole frequency range from 1 to 40 GHz, voltage tunability 4.7% @ 20GHz and 200 kV/cm, lowest loss tangent ~ 0.068 @ 20GHz, K-factor = tunability/tan δ ranged from 124% @ 10GHz to 35% @ 40GHz. BST film CPWIDCs on sapphire showed frequency about 17%, the highest voltage tunability ~ 22.2%, loss tangent ~ 0.137 @ 20GHz, and K-factor = 281% @ 10GHz to 95% @ 40GHz. / QC 20100906

Ferroelectric oxides are a group of advanced electronic materials with a wide variety of properties useful in applications such as memory devices, resonators and filters, infrared sensors, microelectromechanical systems, and optical waveguides and modulators. Among the oxide perovskite-structured ferroelectric thin film materials, sodium potassium niobate or Na0.5K0.5NbO3 (NKN) has recently emerged as one of the most promising materials in radio frequency (rf) and microwave applications due to high dielectric tenability and low dielectric loss. This thesis presents results on growth and structural, optical, and electrical characterization of NKN thin films. The films were deposited by rf-magnetron sputtering of a stoichiometric, high density, ceramic Na0.5K0.5NbO3 target onto single crystal LaAlO3 (LAO), Al2O3 (sapphire), SrTiO3, and Nd:YAlO3, and polycrystalline Pt80Ir20 substrates. By x-ray diffractometry, NKN films on c-axis oriented LaAlO3, SrTiO3 and Nd:YAlO3 substrates were found to grow epitaxially, whereas films on r-cut sapphire and polycrystalline Pt80Ir20 substrates were found to be preferentially (00l) oriented. The surface morphology was explored using atomic force microscopy. Optical and waveguiding properties of the Na0.5K0.5NbO3/substrate heterostructures were characterized using prism-coupling technique. Sharp and distinguishable transverse magnetic and electric propagation modes were observed for NKN thicknesses up to 2.0 μm. The extraordinary and ordinary refractive indices were calculated together with the birefringence of the NKN material. The electro-optic effect in transverse geometry was measured in transmission, where the effective linear electro-optic response was determined to reff = 28 pm/V for NKN/Al2O3 with an applied dc field up to 18 kV/cm. The ferroelectric state in NKN films on Pt80Ir20 at room temperature was indicated by a polarization loop with saturated polarization as high as 33.4 μC/cm2 at 700 kV/cm, remnant polarization of 10 μC/cm2, and coercive field of 90 kV/cm. Current-voltage characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties, with the leakage current density for an NKN IDC on the order of 30 nA/cm2 at 400 kV/cm. Rf dielectric spectroscopy demonstrated low loss, low frequency dispersion, and high voltage tunability. At 1 MHz, NKN/LAO showed a dissipation factor tan δ = 0.010 and a tunability of 16.5 % at 200 kV/cm. For the same structure the frequency dispersion was Δεr = 8.5 % between 1 kHz and 1 MHz. / QC 20100928

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