Navegando por Autor "Soares, Júlia Cristina"

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Processamento de interlantanídeos e investigação de suas propriedades estruturais e vibracionais.
(2016) Soares, Júlia Cristina; Dias, Anderson; Siqueira, Kisla Prislen Félix
Neste trabalho, foi investigada a produção dos interlantanídeos LnLuO3 (Ln = La, Pr, Nd, Sm e Eu) e LaYbO3, os quais constituem uma importante classe de materiais cerâmicos com propriedades físicas e químicas adequadas para diversas aplicações tecnológicas. Os interlantanídeos apresentam interessantes características estruturais, pois dependendo da proporção dos componentes e da diferença de raio iônico dos cátions, o material se cristalizará preferencialmente em um determinado arranjo cristalino. Os interlantanídeos baseados em itérbio e lutécio foram produzidos a partir de precursores nanoestruturados sintetizados via rota hidrotérmica a 250°C durante 24 horas. Os oxi-hidróxidos e hidróxidos produzidos foram calcinados na faixa de temperatura de 800°C a 1600°C durante 2 horas. Observou-se que os precursores foram convertidos em óxidos de lantanídeos, seguido por reações químicas que permitiram a produção dos interlantanídeos puros com estrutura cristalina homogênea em condições otimizadas. As amostras produzidas foram caracterizadas estrutural e morfologicamente utilizando as técnicas de difração de raios X, espectroscopia vibracional Raman e microscopia eletrônica de varredura e transmissão. Os compostos LaYbO3, LaLuO3 e PrLuO3 se cristalizaram na estrutura perovskita ortorrômbica (grupo espacial Pnma, #62), já o interlantanídeo NdLuO3 foi produzido no arranjo cristalino monoclínico (grupo espacial C2/m, #12) e os compostos SmLuO3 e EuLuO3 foram obtidos na estrutura cúbica (grupo espacial Ia-3, #206). As estruturas monoclínica e cúbica para o NdLuO3 e o SmLuO3, respectivamente, foram obtidas pela primeira vez. Os modos ativos Raman para todos os interlantanídeos foram identificados e atribuídos de acordo com a Teoria de grupos para cada estrutura cristalina particular. Palavras-chave: interlantanídeos, síntese hidrotérmica, estrutura cristalina, Espectroscopia Raman.
Structural and thermal evolution studies of LaSbO4 ceramics prepared by solid-state reaction method.
(2013) Siqueira, Kisla Prislen Félix; Borges, Raquel Moreira; Soares, Júlia Cristina; Dias, Anderson
This work investigates the thermal evolution of LaSbO4 ceramics produced by solid-state method in the temperature range 700e1500 _C, for 6 h. Besides the expected phase transitions, a thermal decomposition at high temperatures to La3SbO7 was observed and discussed. The results showed that the phase LaSbO4 can be obtained only below 1450 _C, while temperatures lower than 1100 _C are not able to produce crystalline structures. The samples were submitted to X-ray diffraction and Raman scattering measurements aiming to determine their crystal structures. LaSbO4 materials exhibited monoclinic structures, space group P21/m ¼ C2 2h(#11), with Z ¼ 4. It was verified that all the 36 Raman-active modes predicted by group-theory calculations were observed. Also, the symmetries could be discerned by using polarized Raman scattering, which allow us to assign the gerade modes. Luminescence properties of LaSbO4 were investigated and the results showed that this compound exhibits sensitivity of the host lattice to UV excitation. PL spectra excited at 360 nm have a blue emission band maximum at 428 nm, corresponding to the self-activated luminescence center of LaSbO4.
Structural and vibrational properties of phase - pure monoclinic NdLuO3 interlanthanides synthesized from nanostructured precursors.
(2016) Soares, Júlia Cristina; Siqueira, Kisla Prislen Félix; Moreira, Roberto Luiz; Dias, Anderson
Phase-pure monoclinic NdLuO3 interlanthanides were successfully synthesized from hydrothermalderived precursors. LuO(OH) and Nd(OH)3 materials were firstly obtained by hydrothermal synthesis at 250 _C, for 24 h. X-ray diffraction, micro-Raman spectroscopy, scanning and transmission electron microscopies were employed to investigate the thermal behavior of these precursors and NdLuO3 interlanthanide up to 1600 _C. It was observed that LuO(OH) and Nd(OH)3 were converted to cubic lanthanide oxides below 1000 _C. Cubic Nd2O3 has changed to the monoclinic structure at 1000 _C, followed by reaction with cubic Lu2O3 at 1400 _C to produce monoclinic NdLuO3. Phase-pure monoclinic (C2/m space group, #12) interlanthanide was then produced at 1600 _C for the first time, as confirmed by all the employed techniques. Phonon modes were additionally determined and assigned for this monoclinic structure.
Thermal, vibrational and optical properties of PrLuO3 interlanthanides from hydrothermally-derived precursors.
(2017) Soares, Júlia Cristina; Siqueira, Kisla Prislen Félix; Sousa Filho, Paulo Cesar de; Moreira, Roberto Luiz; Dias, Anderson
PrLuO3 interlanthanides were prepared at temperatures ranging from 800 °C to 1600 °C using hydrothermally- derived precursors. The chemical reactions observed include the conversion and segregation of Pr(OH)3 and LuO(OH), respectively, into PrO2 and Lu2O3 cubic oxides below 1200 °C, followed by the production of a mixture of hexagonal P63/mmc and orthorhombic Pnma PrLuO3 phases at 1400 °C. Phasepure orthorhombic PrLuO3 was obtained at 1600 °C, which was corroborated by Raman and micro farinfrared spectroscopic analyses. Photoluminescence, colorimetric and lifetime measurements were carried out in PrLuO3 samples. Dominant emission verified in samples calcined at 1400 °C corresponds to the hypersensitive 3P0 → 3F2 transition with a color purity of 97% (decay times of 12 μs and 3 μs), while emissions for the phase-pure samples correspond to the 3P0 → 3H6 and 3P0 → 3H5 transitions with a color purity of 94% (a single luminescence lifetime of 12 μs). The optical properties of PrLuO3 interlanthanides thereby suggest that they can be used as luminescent materials in both structural arrangements.