The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
I. Etxebarria - One of the best experts on this subject based on the ideXlab platform.
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Structural instabilities and sequence of phase transitions in SrBi 2 Nb 2 O 9 and SrBi 2 Ta 2 O 9 from first principles and Monte Carlo simulations
Physical Review B, 2015Co-Authors: Urko Petralanda, I. EtxebarriaAbstract:Despite their structural similarities, ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ (SBT) and ${\mathrm{SrBi}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$ (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the Niobium Compound the intermediate phase is suppressed and a direct transition between the high- and low-temperature structures is observed. We present ab initio calculations that reveal the relevance of a trilinear coupling between three symmetry-adapted modes to stabilize the ground state in both Compounds. This coupling is much stronger in SBN than in SBT. Within the framework of the phenomenological Landau theory, it is shown that, by solely increasing the strength of the trilinear coupling, the topology of the phase diagram of SBT can change enough to suppress the intermediate phase. Monte Carlo simulations on an idealized ${\ensuremath{\phi}}^{4}$ Hamiltonian confirm that the trilinear coupling is the key parameter that determines the sequence of phase transitions, and that for higher dimensionality of the order parameters the stability region of the intermediate phase is narrower.
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Structural instabilities and sequence of phase transitions in SrBi$_2$Ta$_2$O$_9$ and SrBi$_2$Nb$_2$O$_9$ from first principles and Monte Carlo simulations
arXiv: Materials Science, 2015Co-Authors: Urko Petralanda, I. EtxebarriaAbstract:Despite their structural similarities, SrBi$_2$Ta$_2$O$_9$ (SBT) and SrBi$_2$Nb$_2$O$_9$ (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the Niobium Compound the intermediate phase is suppressed and a single transition between the high- and low temperature structures is observed. We present \emph{ab initio} calculations that reveal the relevance of a trilinear coupling between three symmetry-adapted modes to stabilize the ground sate in both Compounds, being this coupling much stronger in SBN. Within the framework of the phenomenological Landau theory, it is shown that by solely increasing the strength of the trilinear coupling the topology of the phase diagram of SBT can change up to suppress the intermediate phase. Monte Carlo simulations on an idealized $\phi^4$ Hamiltonian confirm that the trilinear coupling is the key parameter that determines the sequence of phase transitions and that for higher dimensionality of the order parameters the stability region of the intermediate phase is narrower.
Urko Petralanda - One of the best experts on this subject based on the ideXlab platform.
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Structural instabilities and sequence of phase transitions in SrBi 2 Nb 2 O 9 and SrBi 2 Ta 2 O 9 from first principles and Monte Carlo simulations
Physical Review B, 2015Co-Authors: Urko Petralanda, I. EtxebarriaAbstract:Despite their structural similarities, ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ (SBT) and ${\mathrm{SrBi}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$ (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the Niobium Compound the intermediate phase is suppressed and a direct transition between the high- and low-temperature structures is observed. We present ab initio calculations that reveal the relevance of a trilinear coupling between three symmetry-adapted modes to stabilize the ground state in both Compounds. This coupling is much stronger in SBN than in SBT. Within the framework of the phenomenological Landau theory, it is shown that, by solely increasing the strength of the trilinear coupling, the topology of the phase diagram of SBT can change enough to suppress the intermediate phase. Monte Carlo simulations on an idealized ${\ensuremath{\phi}}^{4}$ Hamiltonian confirm that the trilinear coupling is the key parameter that determines the sequence of phase transitions, and that for higher dimensionality of the order parameters the stability region of the intermediate phase is narrower.
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Structural instabilities and sequence of phase transitions in SrBi$_2$Ta$_2$O$_9$ and SrBi$_2$Nb$_2$O$_9$ from first principles and Monte Carlo simulations
arXiv: Materials Science, 2015Co-Authors: Urko Petralanda, I. EtxebarriaAbstract:Despite their structural similarities, SrBi$_2$Ta$_2$O$_9$ (SBT) and SrBi$_2$Nb$_2$O$_9$ (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the Niobium Compound the intermediate phase is suppressed and a single transition between the high- and low temperature structures is observed. We present \emph{ab initio} calculations that reveal the relevance of a trilinear coupling between three symmetry-adapted modes to stabilize the ground sate in both Compounds, being this coupling much stronger in SBN. Within the framework of the phenomenological Landau theory, it is shown that by solely increasing the strength of the trilinear coupling the topology of the phase diagram of SBT can change up to suppress the intermediate phase. Monte Carlo simulations on an idealized $\phi^4$ Hamiltonian confirm that the trilinear coupling is the key parameter that determines the sequence of phase transitions and that for higher dimensionality of the order parameters the stability region of the intermediate phase is narrower.
Luiz C.a. Oliveira - One of the best experts on this subject based on the ideXlab platform.
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Nanostructured Niobium oxyhydroxide dispersed Poly (3-hydroxybutyrate) (PHB) films: Highly efficient photocatalysts for degradation methylene blue dye
Applied Catalysis B: Environmental, 2016Co-Authors: Ana Pacheli Heitmann, Italo R. Coura, Emerson F. Pedroso, P. S.o. Patrício, Agus Mansur, Patterson P Souza, Herman S. Mansur, Luiz C.a. OliveiraAbstract:In this work, nanostructured Niobium oxyhydroxide was dispersed over poly (3-hydroxybutyrate) (PHB), which is a biopolymer, for application as a photocatalyst using visible and UV light. PHB films with different amounts of Niobium oxyhydroxide were characterized by diffuse UV–vis reflectance spectroscopy, FTIR-ATR and SEM. The characterizations showed particles of the Niobium Compound well-dispersed on the polymeric matrix, thus modifying the bandgap value, which improved the photocatalysis process. The material showed excellent catalytic activity (approximately 100% degradation) for the oxidation of methylene blue dye considering the reaction in a continuous flow bath. Moreover, the polymer films were easily removed from the solution after the reaction and reused several times while retaining their high activity. ESI–MS studies showed that the dye removal occurs by the formation of reaction intermediates due to the successive hydroxylation of the dye structure, confirming that the reaction took place improved by photocatalytic conditions.
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Nanostructured oxyhydroxide Niobium (NbO2OH) as UV radiation protector for polypropylene
RSC Advances, 2016Co-Authors: Samara D. Souza, Luiz C.a. Oliveira, Iaci M. Pereira, Ana Pacheli Heitmann Rodrigues, Túlio P. Boaventura, Alexandre R. Souza, Rodrigo Lambert Oréfice, Patrícia Santiago De Oliveira PatrícioAbstract:In this study a novel approach for improving the photo-stabilization of polymers by incorporation of nanoparticles of a new Niobium Compound is reported. For the first time, this approach uses the electronic properties of Niobium oxyhydroxide to absorb UV light efficiently to avoid the decomposition of the polymers. The innovative results of this work consist of preparing nanoparticles of Niobium oxyhydroxide and its modification by treatment with hydrogen peroxide to alter their ability to absorb radiation and act as a photo-stabilizer for preventing polypropylene degradation. Synchrotron radiation was employed: (i) to explore the Niobium nanoparticle form and (ii) to investigate the macromolecular structure of neat PP and PP/Nb Compounds before and after degradation. The results from this research study using FTIR-ATR, DSC and microscopies, as TEM, SEM and OM, indicate that the incorporation of Niobium oxyhydroxide nanoparticles into the PP matrix provides stability against the action of ultraviolet radiation.
Patrícia Santiago De Oliveira Patrício - One of the best experts on this subject based on the ideXlab platform.
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Nanostructured oxyhydroxide Niobium (NbO2OH) as UV radiation protector for polypropylene
RSC Advances, 2016Co-Authors: Samara D. Souza, Luiz C.a. Oliveira, Iaci M. Pereira, Ana Pacheli Heitmann Rodrigues, Túlio P. Boaventura, Alexandre R. Souza, Rodrigo Lambert Oréfice, Patrícia Santiago De Oliveira PatrícioAbstract:In this study a novel approach for improving the photo-stabilization of polymers by incorporation of nanoparticles of a new Niobium Compound is reported. For the first time, this approach uses the electronic properties of Niobium oxyhydroxide to absorb UV light efficiently to avoid the decomposition of the polymers. The innovative results of this work consist of preparing nanoparticles of Niobium oxyhydroxide and its modification by treatment with hydrogen peroxide to alter their ability to absorb radiation and act as a photo-stabilizer for preventing polypropylene degradation. Synchrotron radiation was employed: (i) to explore the Niobium nanoparticle form and (ii) to investigate the macromolecular structure of neat PP and PP/Nb Compounds before and after degradation. The results from this research study using FTIR-ATR, DSC and microscopies, as TEM, SEM and OM, indicate that the incorporation of Niobium oxyhydroxide nanoparticles into the PP matrix provides stability against the action of ultraviolet radiation.
Maxim N Sokolov - One of the best experts on this subject based on the ideXlab platform.
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alnbbr8 preparation crystal structure and vapor pressure studies
Zeitschrift für anorganische und allgemeine Chemie, 2016Co-Authors: A V Rogachev, L N Zelenina, T P Chusova, Alexander V Virovets, Maxim N SokolovAbstract:The ternary Niobium Compound AlNbBr8 (1) was synthesized by degradation of NbS2Br2 in AlBr3 and from elements. Crystal structure and thermodynamic properties of sublimation process were studied.
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AlNbBr8 – Preparation, Crystal Structure, and Vapor Pressure Studies
Zeitschrift für anorganische und allgemeine Chemie, 2016Co-Authors: A V Rogachev, L N Zelenina, T P Chusova, Alexander V Virovets, Maxim N SokolovAbstract:The ternary Niobium Compound AlNbBr8 (1) was synthesized by degradation of NbS2Br2 in AlBr3 and from elements. Crystal structure and thermodynamic properties of sublimation process were studied.