49 documents found, page 1 of 5
Development of carbon quantum dots-based transparent coatings for enhanced UV s...
Silva, Mariana R. F.; Alves, Manuel F. R. P.; Ananias, Duarte; Ivanov, Maxim; Fernandes, Maria Helena V.; Vilarinho, Paula M.; Ferreira, PaulaThe development of easy, translucent, and scalable UV-protection coatings for transparent containers is of utmost importance to ensure the safety of several food and medical products. Here it is studied the preparation of coatings based on carbon quantum dots (C-QDs) with very high absolute emission quantum yields (above 55%) for an excitation wavelenght of 360 nm, and polyvinyl alcohol, using the same temperat...
Nanoscale Study of the Polar and Electronic Properties of a Molecular Erbium(II...
Ivanov, Maxim; Grempka, Arkadiusz; Buryakov, Arseniy; Nikitin, Timur; Justino, Licínia de L. G.; Fausto, Rui; Vilarinho, Paula M.; Paixão, J. A.We successfully synthesized millimeter-sized single crystals of the molecular erbium(III) complex Er(acac)3(cphen), where acac = acetylacetonate and cphen = 5-chloro-1,10-phenanthroline. The novelty of this work stems from the exhaustive examination of the polar and electronic properties of the obtained samples at the macro-, micro-, and nanoscale levels. The single crystal X-ray diffraction method demonstrates...
Local piezo- and ferroelectric properties of γ-glycine single crystal observed ...
Ivanov, Maxim; Buryakov, Arseniy; Khusyainov, Dinar; Silibin, Maxim; Vilarinho, Paula M.; Paixão, José AntónioIn this work, we demonstrate an approach of local mechanical polishing processing to modify the type of intrinsic piezoelectric activity of γ-glycine polymorph grown in a form of a single crystal. By using the piezoresponse force microscopy, the increase in intensity for both out-of-plane (3 times) and inplane (5 times) piezoelectric tensor components is demonstrated. Application of local switching spectroscopy...
FLASH sintering of porcelain stoneware: effect of composition modifications
Ribeiro, Camila; Figueiredo, Luis; Serrazina, Ricardo; Almeida, José C.; Salgado, Joana; Santos, Regina; Jorge, Hélio; Serrão, Álvaro; Marcos, PedroIn this work, we have exploited FLASH sintering as an alternative sintering process in the production of porcelain stoneware. FLASH sintering of porcelain stoneware occurred at temperatures ∼ 1020 °C, for 500 V cm-1, 2 mA mm-2 in 30 s. These conditions are significantly less severe than those typically applied in its conventional sintering, 1150–1250 °C for 1 h. Despite the reduction of time and sintering tempe...
Ultrafast high-temperature sintering of gadolinia-doped ceria
Alemayehu, Adam; Biesuz, Mattia; Javan, Kimia Y.; Tkach, Alexander; Vilarinho, Paula M.; Sglavo, Vincenzo M.; Tyrpekl, VáclavUltrafast high-temperature sintering (UHS) is a rapidly growing research area of material science and engineering. Herein we present UHS of gadolinia-doped ceria (GDC) powders in single and multi-step approaches. The sintered ceramics were characterized from a physical and electrochemical point of view. When the power is applied gradually during the multistep UHS process crack-free GDC ceramics can be obtained ...
High-frequency dielectric properties of K1-xLixTaO3 ceramics compared to crystals
Nuzhnyy, Dmitry; Petzelt, Jan; Bovtun, Viktor; Kempa, Martin; Repček, Dalibor; Tkach, Alexander; Vilarinho, Paula M.; Kamba, StanislavSecond harmonic generation (SHG) and high-frequency dielectric properties of Li-doped KTaO3 (K1-xLixTaO3, KLT100x) ceramics, KLT5 and KLT10, are studied in the 15–300 K temperature range. Using the resonant microwave spectroscopy at 5.8 GHz, time-domain THz spectroscopy (∼10–40 cm−1) and far-infrared reflectivity (∼30–650 cm−1) in conjunction with the dielectric properties earlier published in the 100 Hz – 100 ...
Low-temperature solution processing route for potassium sodium niobate (KNN) th...
Pinho, Rui; Bretos, Iñigo; Jimenez, Ricardo; Calzada, M. Lourdes; Hortigüela, María J.; Otero-Irurueta, Gonzalo; Ivanov, Maxim; Tkach, AlexanderA major challenge for integration of functional oxides, such as ferroelectrics, into microelectronics and flexible electronics is the reduction of their processing temperature, which needs to be lower than the degradation temperature of silicon and flexible plastic substrates. Aiming that, attention has been given to low-temperature processing of oxide films by chemical solution deposition (CSD). In the field o...
Nanostructured transparent solutions for UV-shielding: recent developments and ...
Silva, Mariana R.F.; Alves, Manuel F.R.P.; Cunha, João P.G.Q.; Costa, João L.; Silva, Cristina A.; Fernandes, Maria H.V.; Vilarinho, Paula M.Ultraviolet (UV) radiation is known to promote health concerns that can manifest over both short and long terms. Aging, sunburn, skin cancer, and other conditions are related to UV radiation. Medication can also be negatively affected by this radiation. Moreover, UV radiation modifies the taste, colour, and texture of food, and may compromise its suitability for human consumption. Therefore, the development of ...
Design and Characterization of Novel Barium Strontium Titanate Thick Films for ...
Bouca, Patricia; Figueiredo, Ricardo; Wlodarkiewicz, Anna; Tkach, Alexander; Matos, Joao Nuno; Vilarinho, Paula M.; de Carvalho, Nuno BorgesIn this article, a novel study of the design and characterization of barium strontium titanate (BST) thick films produced by electrophoretic deposition (EPD) on flexible platinum foils is reported. Intended for sub-6 GHz radio frequency (RF) applications, a study on film and electrode thickness is conducted. First, a comparison of tunability and quality factor between different film thicknesses regarding freque...
Elastic moduli of potassium sodium niobate ceramics: Impact of spark plasma tex...
Pinho, Rui; Tkach, Alexander; Carpenter, Michael A.; Noudem, Jacques; Costa, M. Elisabete; Vilarinho, Paula M.An alternative sintering methodology, Spark Plasma Texturing (SPT), allowed us to prepare 98.0% dense lead-free piezoelectric (K1-xNax)NbO3 (KNN) ceramics with a homogenous microstructure of small grains. In this work, Resonant Ultrasound Spectroscopy (RUS) was used to measure bulk, K, and shear, G, moduli of SPT KNN for comparison with conventionally sintered (CS) KNN. SPT fabrication resulted in the highest e...