Until now, lead zirconate titanate (PZT) based ceramics are the most widely used in piezoelectric devices. However, the use of lead is being avoided due to its toxicity and environmental risks. ...Indeed, the attention in piezoelectric devices has been moved to lead-free ceramics, especially on (K,Na)NbO3-based materials, due to growing environmental concerns. Here we report a systematic evaluation of the effects of the compositional modifications induced by replacement of the B-sites with Sb5+ ions in 0.96(K0.48Na0.52)0.95Li0.05Nb1–x Sb x O3-0.04BaZrO3 lead-free piezoceramics. We show that this compositional design is the driving force for the development of the high piezoelectric properties. So, we find that this phenomenon can be explained by the stabilization of a Rhombohedral–Tetragonal (R–T) phase boundary close to room temperature, that facilities the polarization process of the system and exhibits a significantly high piezoelectric response with a d 33 value as high as ∼400 pC/N, which is comparable to part soft PZTs. As a result, we believe that the general strategy and design principles described in this study open the possibility of obtaining (K,Na)NbO3-based lead-free ceramics with enhanced properties, expanding their application range.
The solid-state method was used to synthesize single phase potassium-sodium niobate (KNN) co-doped with the La
-Mn
and Eu
-Fe
ion pairs. Structural determination of all studied solid solutions was ...accomplished by XRD and Rietveld refinement method. Electron paramagnetic resonance (EPR) studies were performed to determine the oxidation state of paramagnetic centers. Optical spectroscopy measurements, excitation, emission and decay lifetime were carried out for each solid solution. The present study reveals that doping KNN with La
-Mn
and Eu
-Fe
at concentrations of 0.5 mol % and 1 mol %, respectively, improves the ferroelectric and piezoelectric behavior and induce the generation of optical properties in the material for potential applications.
Lead-free 0.98(K0.48Na0.52)0.95Li0.05Nb1−xSbxO3–0.02Ba0.5(Bi0.5Na0.5)0.5ZrO3 (KNLNSx–BBNZ) solid solution with 0.04<x<0.08 was prepared by traditional solid-state process. Samples were sintered using ...a conventional method at 1120°C for 4h. The effect of Sb5+ content on the phase structure, microstructure, ferroelectric, dielectric and piezoelectric properties of the KNLNSx–BBNZ ceramics was studied. The phase transition of the ceramic was determined by the temperature dependence of the dielectric properties, while the structural properties, like the phase coexistence, were studied by X-ray diffraction. It was found that ceramics in the composition range of 0.06<x<0.08 possess an orthorhombic (Amm2) and tetragonal (P4mm) phases coexistence. The best piezoelectric properties were obtained in the ceramics with x=0.07: d33=282pC/N, −d31=103pC/N, kp=46%, ɛr=1820, tanδ=3% and Tc=271°C. Furthermore, this composition exhibited a good thermal stability, up to 200°C on d33 piezoelectric constant, indicating that this material have great potential for application from room temperature until this temperature limit.
La solución sólida libre de plomo 0.98(K0.48Na0.52)0.95Li0.05Nb1-xSbxO3-0.02Ba0.5(Bi0.5Na0.5)0.5ZrO3 (KNLNSx-BBNZ) con 0.04<x<0.08 fue sintetizada por el método tradicional de estado sólido. Las muestras se sinterizaron a 1120°C durante 4 horas. Se estudió el efecto del contenido de Sb5+ en las propiedades estructurales, microestructurales, ferroeléctricas, dieléctricas y piezoeléctricas de las cerámicas KNLNSx-BBNZ. La transición de fase de los materiales cerámicos se determinó mediante la dependencia de las propiedades dieléctricas con respecto a la temperatura, mientras que las propiedades estructurales, como la coexistencia de fase, se estudiaron mediante difracción de rayos X. Se encontró que los materiales cerámicos con composición entre 0.06<x<0.08 muestran una coexistencia de fases ortorrómbica (Amm2) y tetragonal (P4mm) (O-T). Las cerámicas con la composición x=0.07 presentaron las mejores propiedades: d33=282pC/N, −d31=103pC/N, kp=46%, ɛr=1820, tanδ =3% y Tc=271°C. Además, se observó una buena estabilidad térmica de la propiedad piezoeléctrica (d33), hasta 200°C, indicando un gran potencial en aplicaciones hasta este límite de temperatura.
Powder samples of Yb3+-doped TiO2 (0.5 mol%) -exhibiting anatase and rutile phases- CaTiO3, SrTiO3 and Na0.5Bi0.5TiO3 were synthesized by the sol-gel and polymeric complex methods. The crystal ...structure, microstructure and optical properties of the powders annealed at 800 °C and 1000 °C for 1 h were investigated by X-ray diffraction, scanning electron microscopy, diffuse reflectance and photoluminescence spectroscopies, respectively. X-ray diffraction patterns show the presence of the expected crystalline phase for each compound. Reflectance spectra for all compounds exhibit a broad absorption band below 425 nm ascribed to the ligand-to-metal charge transfer (LMCT) O2− → Ti4+ fundamental state. The Yb3+ excitation spectra for all titanates show a broadband being also compatible with the LMCT O2− → Ti4+ state, indicating the energy transfer from the host to the Yb3+. Interestingly, the excitation band edges follow the same order as that of the optical bandgap energy of the investigated titanates. A conspicuous excitation band in the CaTiO3:Yb3+ provides evidence about the importance of intrinsic defects in the energy transfer process from the host to Yb3+. Photoluminescence emission and diffuse reflectance spectra in the visible and NIR, reveal an emission band that overlaps with the absorption band of the Yb3+, explaining reasonably well the energy transfer process from the host to Yb3+. According to each compound, the integrated intensity of the Yb3+ emission follows the order Na0.5Bi0.5TiO3 > CaTiO3 > SrTiO3 > TiO2. Finally, it is shown that titanates may downshift photons from UV to wavelengths where a crystalline-silicon photovoltaic solar cell has its higher spectral responsivity.
Sketch of the energy transfer from the O2− → Ti4+ ligand-to-metal charge transfer state (LMCT) to the Yb3+ excited state via intrinsic defect levels. Display omitted
•Yb3+-doped anatase, rutile, CaTiO3, SrTiO3 and (Na0.5, Bi0.5)TiO3 are synthesized.•Yb3+-emission excited through the O2− .→ Ti4+ state in the five titanates is present.•Near infrared photon downshifting from near UV-violet to 1000 nm is achieved.•The energy transfer between the O2− .→ Ti4+ state and Yb3+ is mediated by intrinsic defects.•Stoichiometric changes on Yb3+-doped CaTiO3 support that energy transfer mechanism.
A chabazite-type zeolite was prepared by the hydrothermal method. Before ion exchange, the chabazite was activated with ammonium chloride (NH
Cl). The ion exchange process was carried out at a ...controlled temperature and constant stirring to obtain ion-exchanged chabazites of Ti
chabazite (TiCHA), Zn
chabazite (ZnCHA), Cu
chabazite (CuCHA), Ag
chabazite (AgCHA) and Au
chabazite (AuCHA). Modified chabazite samples were characterized by X-ray diffraction (XRD), scanning electron microscope equipped with energy-dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), N
adsorption methods and UV-visible diffuse reflectance spectroscopy (DRS). XRD results revealed that the chabazite structure did not undergo any modification during the exchange treatments. The photocatalytic activity of chabazite samples was evaluated by the degradation of methylene blue (MB) in the presence of H
O
under ultraviolet (UV) light illumination. The photodegradation results showed a higher degradation efficiency of modified chabazites, compared to the synthesized chabazite. CuCHA showed an efficiency of 98.92% in MB degradation, with a constant of k = 0.0266 min
following a first-order kinetic mechanism. Then, it was demonstrated that the modified chabazites could be used for the photodegradation of dyes.
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•Through DFT, electronic and magnetic properties have been studied in the YIG.•Y3Fe5O12, Y2.75Bi0.25Fe5O12, Y3Fe4GaO12, and Y2.75Bi0.25Fe4GaO12 solid solutions.•Independent ...substitution of Bi3+ induces a reduction in the bandgap of Y3Fe5O12.•The Increase in magnetization is due to the disruption of the magnetic substructures of Fe3+.
The stability, structural, magnetic, and band structure properties of Y3Fe5O12, Y2.75Bi0.25Fe5O12, Y3Fe4GaO12, and Y2.75Bi0.25Fe4GaO12 solid solutions were studied by first-principles calculations. The results demonstrated that the substitution of Bi3+ induces a reduction in the bandgap of Y3Fe5O12. At the same time, Ga3+ was introduced in both the octahedral and tetrahedral sites of Fe3+ and it was found that the bandgap remained almost unchanged. On the other hand, the magnetization was reduced with the incorporation of Bi3+, coinciding with the experimental trend observed in the literature while increasing with Ga3+ incorporation. This behavior is attributed to the disruption of the magnetic sublattices. These results help to understand the ferrimagnetic behavior of YIG and encourage its use as a promising material for optoelectronic and spintronic applications. It is also shown that there is a margin for manipulating the magnetic response through appropriate doping.
β-Tricalcium phosphate (β-TCP) is one of the most investigated calcium phosphates to be used in bone tissue regeneration. Nowadays, β-TCP has been synthetized by different methods that allow ...obtaining different morphologies with chemical compositions similar to the bone tissue, broadening the possibilities of use. In this work, β-TCP powders were obtained using two different routes: mechanosynthesis and sol–gel. Results shown that both methods had significant effects on morphology and size particle of the obtained powders. The average size particles obtained using mechanosynthesis at 24 and 12h of milling time were 1000 and 170nm, respectively. The average size particles of the powders fabricated using sol–gel was 350nm, and the average powder particle size of the sigma reagent was 1450nm. Besides, sol–gel and sigma reagent powders were observed residual phases, instead mechanosynthesis shown only tricalcium phosphate beta phase. The formation of agglomerates with different sizes was observed in both methods by sol–gel and mechanosynthesis.
El fosfato tricálcico fase β (β-TCP) es uno de los fosfatos de cálcico más investigados para el uso de la ingeniería de tejidos óseos. Hoy en día, el β-TCP ha sido sintetizado por diferentes métodos, que han permitido obtener diversas morfologías con composiciones químicas similares a las del tejido óseo ampliando las posibilidades de uso. En este trabajo se obtuvieron polvos de β-TCP usando dos rutas diferentes: mecanosíntesis y sol-gel. Los resultados mostraron que ambos métodos presentan efectos significativos sobre la morfología y el tamaño de partícula de los polvos de fosfato tricálcico. Las partículas de tamaño promedio obtenidas por la ruta de mecanosíntesis con condiciones de 12 y 24h presentaron valores de 1000 y 170nm, respectivamente. Las partículas de tamaño promedio de los polvos fabricados por sol-gel fueron de 350nm y el tamaño promedio del reactivo sigma fue de 1450nm. Además, se observó que los polvos obtenidos por sol-gel y el reactivo sigma presentaron fases residuales, en cambio por mecanosíntesis mostró solo fosfato tricálcico fase beta. La formación de aglomerados se observó en ambos métodos tanto en sol-gel como en mecanosíntesis.
This work reports the first-principles calculations, which describe the structural, magnetic and polar properties of different supercells of ZnO and R-doped ZnO (R = Co2+, Cr2+, Cu2+ and V2+). Here ...the Hubbard approximation was applied in 3d orbitals of some transition metals and in the O-2p, allowing a more realistic approximation of the bandgap and the magnetic properties. The results show a reduction in the bandgap for all doping, from 3.07 eV for ZnO to 1.94 when ZnO is doped with Cu. In turn, the density of states is calculated and ferromagnetic states are induced by unpaired electrons in the transition metals. On the other hand, the ZnO polar state is caused by the relative displacement of ions along the c-axis, and the maximum polarization is observed in V-doped ZnO, which is associated with the decrease in the degree of covalence of ZnO. Thus, simple doping can produce magnetic and polar states, opening up a range of possibilities in the field of multifunctional materials.
•Magnetic and polar effects in ZnO structure doped with Co, V, Cr, and Cu.•Ferromagnetic states in Cr-doped ZnO are produced by unpaired electrons in the transition metals.•Polarization value of 84.76 μC/cm2 for V doped ZnO.
In this work nanostructured powders with nominal composition Y4Zr3O12, undoped and doped at Yb3+ 1 mol%, were synthesized by the polymerizable complex method. The crystal structure, microstructure ...and performance to produce white-light continuous emission spectra of powders under 975 nm continuous laser irradiation were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and optical spectroscopy. Continuous emission spectra of white-light were well-fitted by Planck's law of blackbody radiation. The threshold power values for generating white-light in sample annealed at 800 °C and 1100 °C were 1.36 W and 1.75 W, respectively. This difference was attributed to the crystallite size. The dependence of the absolute temperature, obtained from Planck's law fittings, as a function of the laser's power is explained as due to the microstructural changes, verified by XRD measurements. Finally, a stimulating mechanism of white-light generation involving non-radiative processes of Yb3+ is suggested.
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Synthesis of sodium and potassium–sodium niobates (NaNbO3 and K0.5Na0.5NbO3) was achieved by reducing the reaction time via microwave-assisted hydrothermal route. Sodium niobate was synthesized at ...180°C for 15min using NaOH 6M. During the synthesis of KNN at 180°C, the K4Na4Nb6O19–9H2O intermediate phase appeared. By increasing the temperature to 200 and 220°C, the pure KNN phase was obtained. Potassium–sodium niobate was prepared at 220°C for 15min using KOH/NaOH 8 and 10M. These results were confirmed by X-ray diffraction, Scanning Electron Microscopy and Raman spectroscopy. The NaNbO3 and K0.5Na0.5NbO3 powders consisted of agglomerated pseudo-cubic crystals.
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