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Leyet Y.,University of the East of Cuba | Guerrero F.,University of the East of Cuba | Guerrero F.,Federal University of São Carlos | Perez-Delfin E.,University of the East of Cuba | And 3 more authors.
Phase Transitions | Year: 2012

High-energy ball milling technique was successfully applied to calcinated lead zirconate titanate (PZT 60/40) powders. After 20h of ball milling, large PZT particles were completely broken down, reducing its initial size in three orders of magnitude. Experimental results show a huge sinterability enhancement of the PZT powders by using this technique, achieving its maximum sintering rate at ∼800°C. Relatively low densities (∼91%) were achieved in stoichiometric samples, while in 3% lead excess samples sintered at 950°C for 30, 45, 60, 90 and 120min using a fast firing process and a post-annealing treatment at 800°C for 4 h, densities of ∼97% of the theoretical were achieved. PZT nanostructured ceramics prepared under optimized processing conditions (60h of powder milling, 950°C of sintering temperature, 60min of sintering time and a post-annealing process at 800°C during 4h) show high dielectric constant (ε′) values (900) and low dielectric loss (tan δ) at room temperature and a ferroelectric-paraelectric transition temperature at 375°C. Copyright © 2011 Taylor and Francis Group, LLC.

Leyet Y.,University of the East of Cuba | Guerrero F.,University of the East of Cuba | de la Cruz J.P.,INESCPorto
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2010

The temperature and frequency dependences of the undoped BaTiO3 ceramics dielectric properties were measured between 25 °C and 700 °C and 100 Hz to 10 MHz, respectively. A dielectric anomaly was observed at low frequencies in the temperature range of 400-700 °C. This anomaly was associated to a low frequency dispersion process taking place at high temperature. The relaxation dynamics of the conductive process in BaTiO3 ceramics was investigated. A relaxation function in the time domain (Φ(t)) was determined from the frequency dependence of the dielectric modulus, using a relaxation function in the frequency domain (F*(ω)). In BaTiO3 ceramics context, the best relaxation functions (F*(ω)), in the temperature ranges of 220-400 °C and 425 °C and 630 °C, were found to be a Cole-Cole and Davidson-Cole distribution functions, respectively. The relaxation function (f(t)) obtained by the time domain method was found to be a Kohlrausch-Williams-Watts (KWW) function type. The activation energy values (0.72 eV and 0.8 eV) reveal a mechanism correlated with the movement of single ionized oxygen vacancies and electrons of the second level of ionization, probably due to the formation of a titanium liquid phase during the sintering process. © 2010 Elsevier B.V. All rights reserved.

Pontes M.J.,Ferrari | Coelho T.V.N.,Federal University of Juiz de fora | Carvalho J.P.,INESCPorto | Santos J.L.,INESCPorto | Guerreiro A.,INESCPorto
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

This work discusses remote fiber sensors enabled by optical amplification. Continuous wave numerical modeling based on the propagation of pumps and signal lasers coupled to optical fibers explores Raman amplification schemes to predict the sensor's behavior. Experimental analyses report the results to a temperature remote optical sensor with 50 km distance between the central unit and the sensor head. An electrical interrogation scheme is used due to their low cost and good time response. Different architectures in remote sensor systems are evaluated, where diffraction gratings are the sensor element. A validation of calculated results is performed by experimental analyses and, as an application, the noise generated by Raman amplification in the remote sensors systems is simulated applying such numerical modeling. The analyses of sensors systems based on diffraction gratings requires optical broadband sources to interrogate the optical sensor unit, mainly in long period gratings that shows a characteristic rejection band. Therefore, the sensor distance is limited to a few kilometers due to the attenuation in optical fibers. Additional attenuation is introduced by the sensor element. Hence, to extend the distance in the optical sensor system, the optical amplification system is needed to compensate the losses in the optical fibers. The Raman amplification technology was selected mainly due to the flexibility in the gain bandwidth. The modeling can be applied to sensor systems that monitor sites located at long distances, or in places that the access is restricted due to harsh environment conditions in such cases conventional sensors are relatively fast deteriorated. © 2013 SPIE.

Romaguera-Barcelay Y.,INESCPorto | Romaguera-Barcelay Y.,University of Porto | Agostinho Moreira J.,University of Porto | Gonzalez-Aguilar G.,INESCPorto | And 3 more authors.
Journal of Electroceramics | Year: 2011

A novel and general chemical solution route for processing high-quality transition metal and rare-earth orthorhombic manganite thin films on Pt(111)/Ti/SiO2/Si substrates was reported. The precursor solutions decomposition process of the manganites was studied by TG and DTA techniques, showing the formation of the phase above 650°C in LaMnO3 and 750°C in both EuMnO3 and DyMnO3 thin films. X-ray diffraction and Raman spectroscopic analysis reveal the formation of a pure orthorhombic structure, with a space group Pbnm, in LaMnO3, EuMnO3 and DyMnO3 thin films annealed at temperatures above the TG phase formation temperature observed. Microstructure and grain morphology of the films were analyzed by SEM and AFM techniques, showing a progressive improvement of the films structures with the increase of the annealing temperature. The temperature dependence of the magnetic response of the LaMnO3, EuMnO3 and DyMnO3 thin films show typical transition temperatures, compared with those reported for lanthanum, europium and dysprosium manganite single crystals and ceramics. © 2011 Springer Science+Business Media, LLC.

Shamsuzzoha A.,University of Vaasa | Kankaanpaa T.,University of Vaasa | Carneiro L.,INESCPorto
2011 17th International Conference on Concurrent Enterprising, ICE 2011 - Conference Proceedings | Year: 2011

State-of-the-art customization strategies help manufacturing organizations to better fulfill customers' expectation. There is a need to adopt suitable strategic options with the view to develop product variants with minimum lead time and cost. In such perspectives, platform-based product family is an important concept that supports the efficient manufacturing of a stream of product variants created from the basic platform. This approach supports the true customization strategy and especially suitable in the case of customize-to-order (CTO) production scenario, where various modules or components are added or replaced on the basic platform to bring customized variants. Specific module or feature known as white spot can also be added on the common platform to bring the option to specify and manufacture an individualized product. The CTO scenario can be performed in a collaborative manner, where the corresponding partners actively taking part in the product development process to achieve potential benefits such as resource sharing, exchanging of innovative ideas and expertise, higher market segment, etc. This research investigates the outcomes from collaborative platform-based product family approach in terms of assuring higher customization and profitability. © 2011 Research Institute for Ope.

Romaguera-Barcelay Y.,INESCPorto | Romaguera-Barcelay Y.,University of Porto | Moreira J.A.,University of Porto | Almeida A.,University of Porto | De La Cruz J.P.,INESCPorto
Thin Solid Films | Year: 2012

Hexagonal LuMnO 3 thin films have been prepared based on a chemical solution deposition method. These films were deposited by spin-coating technique and annealed at different temperatures from 750 °C up to 850 °C, based on the thermogravimetric and differential thermal analysis results. An amorphous phase is observed in the film annealed at 750 °C, while a pure LuMnO 3 hexagonal phase is reached in the films annealed at 800 °C and 850 °C, along with a visible enhancement in the grain morphology as the annealing temperature increase. Low temperature magnetic analysis of the LuMnO 3 films annealed at 850 °C reveals several magnetic transitions, which are consistent with those reported for both LuMnO 3 ceramics and single crystals. Moreover, the emergence of a canted spin arrangement was evidenced from the temperature dependence of the specific induced magnetization and magnetic hysteretic cycles. No significant effect of the substrate on the magnetic properties was also sorted out. Dielectric measurements reveal the existence of a complex frequency behavior of the dielectric permittivity, which can be associated with relaxation processes arising from the interfaces film/electrodes. © 2011 Elsevier B.V. All rights reserved.

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