Structural and electrical properties of Zr-doped K0.48 Na 0.52 NbO 3 ceramics: “Hard” lead-free piezoelectric

The structural and electrical properties of K0.48Na0.52Nb1−xZrxO3−δ (x = 0–0.04) ceramics prepared by the conventional solid-state reaction method were studied. Pellets with composition x ≤ 0.03 sintered at 1125 °C for 2 h showed single-phase of potassium sodium niobate (KNN) perovskite structure. Based on X-ray diffraction and Raman results, a mixture of orthorhombic and monoclinic phases was observed in intermediate compositions. The addition of Zr improved the sinterability and the “hard” piezoelectric properties of KNN, increasing the Ec and Qm values. The composition with x = 0.03 presented the highest permittivity at room temperature, ɛr′ = 363 and the lowest dielectric losses, tan δ = 0.027. Moreover, it was the sample with the highest Qm and d33 values, with Qm = 1781 and d33 = 82 pC/N. It was therefore the best compositions to obtain a “hard” piezoelectric material based on Zr-doped KNN, which makes it promising candidate for use as “hard” lead-free piezoelectric material for high power applications

Induced p-type semiconductivity in Mg-doped Nd2Zr2O7 pyrochlore system

Heterovalent B-site MgO substitution in the Nd2Zr2O7-system (Nd2Zr2−xMgxO7−x) has been explored. The pyrochlores were synthesized by a polymeric sol-gel method and characterized by X-ray diffraction (XRD), Raman spectroscopy and Scanning Electron Microscopy to determine structure, phase composition and microstructure. Impedance Spectroscopy (IS) was employed to study the electrical behavior of the ceramics over the ranges 200–800 °C and under pure N2 and O2. The XRD showed that the solid solution limit was x > 0.02 and all the materials show a cubic ̅ structure. The Raman results confirm the structural disorder created by the introduction of Mg2+ and the subsequent generation of oxygen vacancies. The IS data shows a dramatical increase of the oxide-ion conductivity when doping and that the conductivity depends strongly on the atmosphere, leading to p-type semiconductivity under pure O2 atmosphere. The present study highlights the use of heterovalent dopants to drastically increase the oxide-ion conductivity of pyrochlore-like materials

The catalytic activity of the Pr2Zr2-xFexO7±d system for the CO oxidation reaction

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO2, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr2Zr2-xFexO7±d (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO2 sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction.Postprint (published version

Semblanza de la Profesora Purificación Escribano. A la Profesora Dra. Purificación Escribano López, en recuerdo

Nota póstuma dedicada a la Profesora Purificación Escribano López, Catedrática de Química Inorgánica en la Universitat Jaume I de Castelló. El artículo repasa los aspectos más relevantes de su obra y de su trabajo como docente e investigadora en la universidad de Castelló

Supporting Information: A site-selective fluorescence spectroscopy study of the crystal phases of KY3F10: Leveraging the optical response of Eu3+ ions

S1. Rietveld Refinement: The experimental powder X-ray diffraction pattern of sample 1DA was refined using the Rietveld method by means of GSAS software. A Pseudo-Voight function was used to simulate the peak shape and the log-interpolate function with ten coefficients was used to simulate the background. The Rietveld refinement graphic is depicted in Figure S1, while the refined parameters (including the percentage of phase fraction) are included in Table S1 and Table S2.S2. Structural Characterization: Figure S2 shows the FT-IR spectra of samples 1D (δ), 1DA (δ + α), and 1A (α) as an example of the different crystal phases. The broad, weak bands at ≈ 3100–3500 cm–1 and ≈ 1640 cm–1 are assigned to the O–H stretching vibrations and H–O–H bending mode of H2O molecules, respectively. This indicates the presence of some absorbed water in the materials. In sample 1D, a notable difference is appreciated in the stretching and bending vibrational modes of H2O molecules, since they are associated with crystalline water molecules localized in the channels of the δ-KY3F10·xH2O host lattice. These bands are sharper and stronger. For all the samples, the Y–F host lattice vibrations were observed below 600 cm–1 . On the other hand, the FT-IR spectrum of sample 1DA can be interpreted as a combination of the spectra of samples 1D and 1A, which is very good agreement with the results of XRD and the coexistence of δ and α crystal phases in the same sample. It is observed a major response from the response of the α-phase (see indeed the Y–F host lattice vibrations), a fact that suggests that there is a higher amount of this crystal phase.S3. DLS measurements: Figure S3 shows the particle size distribution of samples doped with 1 mol% Eu 3+ content. For the DLS measurements, the powder concentration was 1 mg/mL in distilled water. Sample 1DA (α + δ) was previously filtered using a 0.4 µm cellulose filter to eliminate the agglomerates corresponding to the α-phase. Otherwise, neither a good dispersion nor good data from the DLS measurements could be obtained. The maximum peak for sample 1DA-filtered was found at 195 nm (mainly due to the δ-phase nanospheres), which is quite close to the value obtained for sample 1D (δ-phase), 175 nm. The obtained hydrodynamic diameters were in very good agreement with the SEM results.Peer reviewe

Evaluation of Pr2Zr2-xCexO7±δ pyrochlores as a potential Cu support catalysts for CO oxidation in simulated GDI conditions

This study evaluates the catalytic activity, both as bulk catalysts and as supports for copper catalysts for CO oxidation in a simulated Gasoline Direct Injection Engine (GDI) of two pyrochlores: Pr2Zr2O7 (PZ) and Pr2Zr1.9Ce0.1O7±δ (PZC). These pyrochlores were synthesized by the solvothermal method. XRD, FE-SEM, HR-TEM, XPS, H2-TPR, and O2-TPD characterization techniques were employed to determine the structural, microstructural, and redox properties of the samples. All materials exhibited high catalytic activity for CO oxidation, with Cu-PZC showing the best performance, which is comparable to that of a 1% Pt/Al2O3 commercial catalyst used as a reference. Thus, the synthesized solids could be a promising and cost-effective alternative to noble metal-based catalysts used to control GDI exhaust gas composition.H.B-M, E.C. and E.L.S.V. thank the Spanish Government (Ministerio de Ciencia e Innovación, Project PID2020-116149GB-I00) for the financial support. E.L.S.V thanks the Generalitat Valenciana for the predoctoral contract (GRISOLIA/2019/054) and for the financial support for the international stay (CIBEFP/2021/22). A.D-V and MJ.I-G thank the Spanish Government (Ministerio de Ciencia e Innovación, Project PID2019-105542RB-I00), the European Union (FEDER Funds) and the Regional Government (Generalitat Valenciana, Project CIPROM/2021-070) for the financial support. A.D-V thanks the University of Alicante the financial support for the predoctoral contract

Understanding the rapid reoxidation process and the electrical properties of Spark Plasma sintered pyrochlores

Pyrochlore structures with composition Pr2−xSmxZr2O7 (x = 0, 1, and 2) were synthetized and studied. Spark Plasma Sintering (SPS) was employed to produce ceramics with over 95% of relative density. The reoxidation behavior and the influence of the sintering process on the electrical properties were studied by Electrochemical Impedance Spectroscopy. The overall conductivity of the materials is higher for the samples with Pr, while the introduction of Sm induced an additional electrical contribution. The reoxidation of the samples presented fast kinetics and increased conductivity, particularly in the PrSmZr2O7 (PSZO) sample. PSZO also exhibits a total conductivity comparable to that of the reference materials used as ionically conductive solid electrolytes. The prepared ceramics, especially the PSZO sample, demonstrate excellent relative density, good conductivity, and fast oxidation, holding promise for applications such as Solid Oxide Fuel Cells, gas sensors, and clean energy technologies that require thermal and physical stability, as well as rapid oxidation-reduction processes