Defect chemistry of mixed conducting double Perovskites

Barium Gadolinium Lanthanum Cobaltites with the general formula Ba1-xGd0.8-yLa0.2+x+yCo2O6-δ (BGLC) are reported as Mixed Proton and Electron Conducting materials (MPECs), and have been utilized as positrode (positive electrode) materials for Proton Ceramic Electrochemical Cells (PCECs) [1]. A defect chemical model, treating various charge carrying defects in BGLC was published in 2017 [2] and in this work we expand the model to also comprise formation of protons in BGLC. Protons can be incorporated by two different reactions, in a ratio depending on measurement conditions and the oxidation state of the material. Low temperatures and high pO2 leaves BGLC oxidized, and with increasing electron hole concentration, the hydrogenation reaction is promoted with respect to hydration. Hydrogenation is confirmed by use of isothermal Dry-H2O-D2O switches in thermogravimetric measurements, revealing a larger concentration of protons than expected from hydration only (Figure 1, left). The reduction of BGLC by hydrogenation is slowly counteracted by oxygen uptake combined with an expected cation reordering, bringing the material back to its initial oxidation state after equilibration in wet conditions. By combining oxidation and hydration thermodynamics, hydrogenation entropy and enthalpy can be obtained, making it possible to model proton concentrations from hydration and hydrogenation separately by use of advanced defect chemistry (Figure 1, right). Hydration is proposed to be facilitated by a minor concentration of oxygen vacancies in the O-Co-O layers, where acidic vacancies may accommodate basic hydroxyl groups. These vacancies are neighboured by more basic oxide ions in the O-Ba-O and O-Ln-O layers which in turn may accommodate protons. Please click Additional Files below to see the full abstract

Terbium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties

The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La1−xTbxNbO4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 °C, and 530 °C for La0.9Tb0.1NbO4+δ, La0.8Tb0.2NbO4+δ, and La0.7Tb0.3NbO4+δ, respectively. The impedance spectroscopy results suggest mixed conductivity of oxygen ions and electron holes in dry conditions and protons in wet. The water uptake has been analyzed by the means of thermogravimetry revealing a small mass increase in the order of 0.002% upon hydration, which is similar to the one achieved for undoped lanthanum orthoniobate

Praseodymium Orthoniobate and Praseodymium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties

In this paper, the structural properties and the electrical conductivity of La1−xPrxNbO4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) and PrNbO4+δ are presented and discussed. All synthesized samples crystallized in a monoclinic structure with similar thermal expansion coefficients. The phase transition temperature between the monoclinic and tetragonal structure increases with increasing praseodymium content from 500 °C for undoped LaNbO4+δ to 700 °C for PrNbO4+δ. Thermogravimetry, along with X-ray photoelectron spectroscopy, confirmed a mixed 3+/4+ oxidation state of praseodymium. All studied materials, in humid air, exhibited mixed protonic, oxygen ionic and hole conductivity. The highest total conductivity was measured in dry air at 700 °C for PrNbO4+δ, and its value was 1.4 × 10−3 S/cm

Properties of New Composite Materials Based on Hydroxyapatite Ceramic and Cross-Linked Gelatin for Biomedical Applications

The main aim of the research was to develop a new biocompatible and injectable composite with the potential for application as a bone-to-implant bonding material or as a bone substitute. A composite based on hydroxyapatite, gelatin, and two various types of commercially available transglutaminase (TgBDF/TgSNF), as a cross-linking agent, was proposed. To evaluate the impacts of composite content and processing parameters on various properties of the material, the following research was performed: the morphology was examined by SEM microscopy, the chemical structure by FTIR spectroscopy, the degradation behavior was examined in simulated body fluid, the injectability test was performed using an automatic syringe pump, the mechanical properties using a nanoindentation technique, the surface wettability was examined by an optical tensiometer, and the cell viability was assayed by MTT and LDH. In all cases, a composite paste was successfully obtained. Injectability varied between 8 and 15 min. The type of transglutaminase did not significantly affect the surface topography or chemical composition. All samples demonstrated proper nanomechanical properties with Young’s modulus and the hardness close to the values of natural bone. BDF demonstrated better hydrophilic properties and structural stability over 7 days in comparison with SNF. In all cases, the transglutaminase did not lead to cell necrosis, but cellular proliferation was significantly inhibited, especially for the BDF agent

Structural Properties and Water Uptake of SrTi1−xFexO3−x/2−δ

In this work, Fe-doped strontium titanate SrTi1−xFexO3−x/2−δ, for x = 0–1 (STFx), has been fabricated and studied. The structure and microstructure analysis showed that the Fe amount in SrTi1−xFexO3−x/2−δ has a great influence on the lattice parameter and microstructure, including the porosity and grain size. Oxygen nonstoichiometry studies performed by thermogravimetry at different atmospheres showed that the Fe-rich compositions (x > 0.3) exhibit higher oxygen vacancies concentration of the order of magnitude 1022–1023 cm−3. The proton uptake investigations have been done using thermogravimetry in wet conditions, and the results showed that the compositions with x < 0.5 exhibit hydrogenation redox reactions. Proton concentration at 400 °C depends on the Fe content and was estimated to be 1.0 × 10−2 mol/mol for SrTi0.9Fe0.1O2.95 and 1.8 × 10−5 mol/mol for SrTi0.5Fe0.5O2.75. Above 20 mol% of iron content, a significant drop of proton molar concentrations at 400 °C was observed. This is related to the stronger overlapping of Fe and O orbitals after reaching the percolation level of approximately 30 mol% of the iron in SrTi1−xFexO3−x/2−δ. The relation between the proton concentration and Fe dopant content has been discussed in relation to the B-site average electronegativity, oxygen nonstoichiometry, and electronic structure