TATIANE DA SILVA NASCIMENTO

TATIANE DA SILVA NASCIMENTO

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Magnetic properties of Er-doped Fe3O4 nanoparticles studied by perturbed angular spectroscopy
2019 - CORREA, E.L.; BOSCH-SANTOS, B.; SALES, T.S.N.; CABRERA-PASCA, G.A.; CORREA, B.S.; CARBONARI, A.W.; OLESHKO, V.P.; DENNIS, C.L.
Investigation of HfO2 and ZrO2, separately and also in the form of mixtures, pure and doped with Si
2019 - NASCIMENTO, CARLOS E.; SALES, TATIANE da S.N.; CARBONARI, ARTUR W.
The HfO2 has been used in several technological applications, one of which is the replacement of silicon oxide as the material for the door in the manufacture of CMOS-FET devices [1]. ZrO2 also has several applications, being more used in the form of solid electrolytes and oxygen sensors and also in electrochemical pumps. Due to the similarity of the size and properties, that is found in the proportion of 1 to 2 % in the ore of this one. Since the ions of these elements are nearly identical in size, the separation is difficult, and is in most cases unnecessary due to the similarity of its properties [2]. Doping with other elements improves the specific characteristics of HfO2 and ZrO2, making them useful for different applications and extending their uses in CMOS-FET devices. It also reduces the ZrO2 defects, such as its low resistance to high temperatures, causing in the formation of polycrystalline films and decreasing the dielectric constant that can occur due to leakage current in the grain boundaries, making it necessary to use an amorphous interface to reduce losses. In addition, grain size and orientation change throughout a polycrystalline film, which can cause variations in the value of producing irreproducible properties [3]. In this project the atomic scale investigation of HfO2 and ZrO2 was carried out separately and also in the form of pure, doped mixtures with Si [4]. They were used (RBS), X-ray Diffraction [5] and SEM for caracterization. The PAC technique was used to measure the hyperfine parameters, such as the electric field gradient (Vzz), the asymmetric parameter of the electric field gradient (η) and the possible magnetic hyperfine field over a wide temperature range (from 10 to 1300 K). The measurements were performed in order to correlate the results with the behavior of the characteristic properties of each compound to understand the microscopic mechanisms that give rise to these phenomena [6].
Study of hyperfine interactions in Perovskite structure CaTiO3 with perturbed angular correlation spectroscopy
2019 - LEITE NETO, O.F.S.; SANTOS, B.S.; NARESSI, A.L.E.; SALES, T.S.N.; SAXENA, R.N.; CARBONARI, A.W.
Ceramic materials of the perovkista were identified as candidates for immobilization of medium and high levels of radioactive waste due to the fact that they are thermodynamically chemically and physically stable. Because it is a nuclear technique, PAC spectroscopy has great precision and efficiency in the measurement of local hyperfine fields on an atomic scale, constituting an ideal tool for the investigation of the atomic origin of structural phenomena, such as the influence of defects in the macroscopic properties of many materials or the local neighborhood of metallic atoms in the oxide structure. The samples has been prepared by sol-gel method and characterized by X-ray diffraction. In this study the time differential perturbed angular correlation (PAC) spectroscopy was used to study the structure of CaTiO3 and the possible defects made by radiation exposure. The probe nucleus used in this research was 111Cd. The PAC method is based on the hyperfine interaction of nuclear moments of the probe with extra nuclear magnetic fields or electric field gradients (EFGs). In the case of quadrupolar electric interaction, the experimental measurement gives the quadrupolar frequency νQ with respective distribution δ as well as the asymmetry parameter η of EFG. The γ-γ PAC measurements were carried out using a standard set up with four conical BaF2 detector scintillators with a time resolution of 0.6 ns (FWHM).
RE-doped Fe3O4 (RE = Eu, Gd, Er) nanoparticles for nanothermometry
2019 - CORREA, E.; BOSCH-SANTOS, B.; SALES, T.; CABRERA-PASCA, G.; CORREA, B.S.; NETO, O.F.; CARBONARI, A.W.; OLESHKO, V.; DENNIS, C.
Temperature affects every physical system, chemical reaction, and biological process. A new method, magnetic nanothermometry, is being explored to measure temperature throughout a volume. This method uses large changes in magnetization as function of temperature, which cannot be obtained with current magnetic nano-objects (MNO). To get a large magnetization change we have examined the magnetic properties of RE-doped Fe3O4 (RE = Eu, Gd, Er) MNO. Samples were synthesized by co-precipitation. For the doped material, RE+3 were chosen in order to replace the Fe+3 in the (Fe+2)(Fe+3)2O4 structure. Structural characterization was performed by X-ray diffraction and transmission electron microscopy. Hyperfine interaction parameters as a function of temperature (300 K to 873 K) were obtained by perturbed angular g-g correlation (PAC) spectroscopy using 111In(111Cd) as probe nuclei. To fit the PAC spectra, the 111Cd probes were considered to occupy three sites: tetrahedral, octahedral, and a third site where the probes are located at the nanoparticle surface [1]. The hyperfine magnetic field Bhf was calculated using the Larmor equation, and its behavior as a function of temperature follows a Brillouin-type transition. For example, the Curie temperature (TC) obtained for 5% Er-doped was approx. 846 K (FIG. 1), which is higher than the expected TC for pure Fe3O4 (approx. 722 K) [2]. Magnetization as a function of temperature shows a 70 % change in magnetization around 100 K for Er-doped Fe3O4 (FIG.2), which is an improvement in temperature on pure Fe3O4 (below 50 K) [3]. Current work is focused on correlating the temperature range in which the magnetization change occurs and determining if it depends on the dopant element.
Study of the hyperfine parameters in Si and Fe doped HfO2 nanoparticles by perturbed angular correlation spectroscopy
2019 - SALES, T.S.N.; SAXENA, R.N.; CARBONARI, A.W.
Nanoparticles (NPs) have attracted a great deal of interest due to their desirable properties suited for technological and medical applications. Hafnium dioxide (HfO2) can be used in both areas. HfO2 NPs were synthesized through sol-gel method, which allows an efficient and controlled doping of HfO2. In this work, we have investigated the effect of (5% at.) doping of HfO2 NPs with Si and Fe by measuring hyperfine interactions at 181Ta probe nuclei on Hf sites using the perturbed γ–γ angular correlations (PAC) spectroscopy. The structural and morphological analysis was carried out by X-ray diffraction (XRD) and transmission microscopy (TEM) techniques. For both samples, XRD results showed a single phase with the expected monoclinic structure and TEM results indicated NPs with an average diameter of approximately 30 nm. The hyperfine parameters were measured in the temperature range of 200-900 ºC. The radioactive 181Hf was produced by irradiating the samples with neutrons in the IEA-R1 reactor at IPEN. The samples were enclosed in the alumina tube instead of usual silica tube to avoid the formation of hafnon. Results of both samples showed that probe nuclei occupy three sites with different electric quadrupolar interactions. The major fractions (~65%), in both cases however, showed the well-known monoclinic structure of pure HfO2 [1]. The characterization of one of the minor fractions in Si doped HfO2 showing a tetragonal structure between 400-600 ºC is discussed.
Magnetic field at Ce impurities in La sites of LaBaMn2O6 double perovskites
2019 - BOSCH-SANTOS, B.; NASCIMENTO, N.; SAIKI, M.; CORREA, E.L.; SALES, T.S.; PEREIRA, L.F.; CABRERA-PASCA, G.A.; CARBONARI, A.W.
Magnetic behavior in LaBaMn2O6 double perovskite compounds has been investigated with various techniques, due to the rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine field at the 140Ce nucleus of Ce impurities occupying La sites. The radioactive 140La nuclei with a half-life of 40.8 h were produced by direct activation of natural La present in the samples through the irradiation with neutrons in the IEA-R1 nuclear research reactor of IPEN. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. This double perovskite samples were synthesized by sol-gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group. This phase occurs due to an oxygen deficiency. The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites, which can be ascribed to the contribution of 4f band of Ce to Bhf at low temperatures due to the increase in its localized character.
Magnetic field at Ce impurities in La sites of La0.5Ba0.5MnO3 double perovskites
2019 - BOSCH-SANTOS, B.; NASCIMENTO, N.M.; SAIKI, M.; CORREA, E.L.; SALES, T.S.N.; PEREIRA, L.F.D.; CABRERA-PASCA, G.A.; SAXENA, R.N.; SCHELL, J.; CARBONARI, A.W.
Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol- Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and a pure antiferromagnetic interaction below 100 K. Moreover, it also indicates an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites measured with 140Ce probe nuclei, which can be ascribed to the contribution of 4f band of Ce to Magnetic Hyperfine Field (Bhf) at low temperatures due to the increase in its localized character.
Low temperature synthesis of pure and Fe-doped HfSiO4: Determination of Si and Fe fractions by neutron activation analysis
2019 - SALES, T.N.S.; BOSCH-SANTOS, B.; SAIKI, M.; BURIMOVA, A.; PEREIRA, L.F.D.; SAXENA, R.N.; CARBONARI, A.W.
A new method of synthesis of hafnium silicate HfSiO4 (also known as hafnon) is reported. We observed a selfcontrolled incorporation of SiO2 from the quartz tube in which a sample of hafnium oxide nanoparticles was heated. This approach was then adapted to Fe-doped hafnon production. Sample structure, morphology and composition were characterized by X-ray diffraction, electron microscopy and neutron activation analysis. Diffraction data has shown that lattice parameters of doped HfSiO4 thus obtained are very close to those previously known for bare hafnon. The hafnon-like phase stabilized at T=900 °C which is about 500 °C lower than the corresponding transition of bare bulk hafnium silicate. The fractions of Si and Fe in the composite matrices were determined with neutron activation analysis. These results completed by X-ray diffraction data allowed to assume that (i) Fe initially substituted Hf in the HfO2 lattice; (ii) there was no migration of iron atoms from Hf to Si sites at the formation of hafnon-like phase; (iii) doped and undoped hafnium oxide has taken as much Si from the quartz as was needed for the arrangement of Fe1-xHfxSiO4 tetragonal system, 0≤x<0.2. Our results are consistent with those obtained for similar materials, such as metal (Fe,V) doped zircon, where the dopant also demonstrated catalytic effect on phase stabilization.
Estudo de interações hiperfinas em materiais nanoestruturados de HfO2 dopados com Si, Fe, Y, La e HfSiO4 dopado com Fe pela técnica de correlação angular gama-gama perturbada
2018 - SALES, TATIANE da S.N.
No presente trabalho é apresentado o estudo sistemático das interações hiperfinas, em compostos de óxido de háfnio (HfO2) dopados com silício (Si), ferro (Fe), ítrio (Y) e lantânio (La) em porcentagens de 5% e 10%. A técnica aplicada para esse estudo foi o de correlação angular gama-gama perturbada (CAP) utilizando o núcleo de prova 181Hf(181Ta). Além disso, o estudo também foi estendido para o háfnio (Hf) na estrutura de ortosilicatos (HfSiO4) dopado com 20% Fe e na forma de filmes finos de HfO2. As amostras foram produzidas pelo método sol gel e para os filmes finos foi utilizado a técnica de spin coating. A caracterização estrutural destas amostras foi pela técnica de difração de raios-X e para morfologia foi utilizada as microscopias eletrônicas de varredura e transmissão. O núcleo de prova 181Hf(181Ta) presente na rede cristalina de todos os compostos forneceu os resultados da frequências de quadrupolo elétrico para o sitio monoclínico do óxido de háfnio (m- HfO2) bem caracterizado e um segundo sítio relacionado as vacâncias de oxigênio e defeitos na rede cristalina do HfO2. Além disso, as medições CAP que foram realizadas para as amostras de HfO2 dopadas, apresentam a formação de um terceiro sítio que está relacionado com o tamanho da partícula e a dopagem. Para o composto de HfSiO4 os resultados CAP indicam a temperatura de difusão do silício (Si), por volta de 700 °C e para o Fe- HfSiO4 mostra a influência do ferro na nucleação do composto que é superior em 30% em relação ao HfSiO4. Para as amostras de filmes finos os resultados CAP evidenciam os efeitos de superfície observado pelo surgimento de um terceiro sítio, ao longo do tratamento térmico 200 - 900 °C durante a medida. Este sítio também foi observado em temperaturas ambiente.
Tuning the dielectric response of HfO 2 nanoparticles by Si-doping
2018 - SALES, T.S.N.; BURIMOVA, A.; CARBONARI, A.W.; BOSCH-SANTOS, B.; PEREIRA, L.F.D.
The properties of bulk materials and corresponding nanostructures may differ significantly which leads to distinct scopes of their applications. As the miniaturization continues, nanostructures show great potential in microelectronics. Among others, nanostructured hafnium (IV) oxide (hafnia, HfO 2 ) has attracted considerable attention due to its chemical stability and physical characteristics 1 . It has high dielectric constant ( ∼ 25) and is relatively thermally stable (melting point at 3085 K) 2 . These qualities have made hafnia an alternative to SiO 2 for gate oxide layers in field-effect transistors, since the leakage current issue and consequent thickness limitations of silica were hindering miniaturization. Clearly, the features of HfO 2 can be further tuned by doping 3 . Understanding the relation between the macro-properties of such complex systems and their architecture at atomic scale should help select doping parameters adequate for particular applications. In this work 0at%, 5at% and 10at% Si-doped HfO 2 nanoparticles (NPs) were synthesized via sol-gel method. Basic characterization included scanning/transmission electron microscopy, electron backscattering and X-ray diffraction. NPs were demonstrated to have spherical shape, sizes in the range of 10─40nm and monoclinic structure (m-HfO 2 ). Local structure and electronic environment of the samples was probed with perturbed angular correlation (PAC) spectroscopy. Sample irradiation resulted in the formation of 181 Hf isotopes (PAC probes 4 ) at several sites whose decay to 181 Ta is preferentially through an intermediate (metastable) state with lifetime depending strongly on local extra-nuclear fields. Thus, time distribution of decay probability provided information on the ambient of the probe. For undoped sample PAC data has revealed two distinct Hf sites, one of those possessing well-defined quadrupole frequency ν Q ≈ 750 MHz and electric field distribution asymmetry η ≈ 0.36. Site occupation raised with temperature from 16% at T = 473K to 75% at T = 1073K, which agrees with the results found in the literature for the quadrupole interactions of 181 Ta in m-HfO 2 4 . For the doped samples (both Si 5at% and 10at%) additional site was observed. Symmetrical electric field distribution ( η = 0) and a greater site fraction at T = 673─873K allowed to attribute it to a tetragonal phase of hafnia. First principles analysis has shown that doping m-HfO 2 with certain cations can induce the formation of tetragonal phase 5 . We emphasize that this phase is desirable for transistor applications since it is associated with the highest dielectric constant.