Study on thermolysis process of a new hydrated and protonated perovskite-like oxides H2K0.5Bi2.5Ti4O13·yH2O (original) (raw)
Low-temperature aqueous synthesis (LTAS) of ceramic powders with perovskite structure
Journal of Materials Science Letters, 1996
Barium metatitanate is among the most extensively employed ceramics for electronic applications, mainly in the form of miniaturized multilayer and grain boundary layer capacitors with large capacitance values for energy storage. It can also be employed in the field of acoustic transducers, where it can be competitive with PZT when a good hydrostatic response is required. A very fine grained microstructure is often required for many practical purposes, which is, however, difficult to achieve through traditional preparation methods [1]. Considerable effort has been devoted to discovering alternative syntheses to obtain fine powders, especially via metallo-organic precursors . Recently, submicron BaTiO3 crystalline powder has been prepared in our laboratory using a low-temperature aqueous synthesis (LTAS) . Due to the very fine particle size (diameter <0.03#m), relative lowtemperature sintering is possible which reduces grain growth. High purity and reproducibility are achieved through this procedure; excellent control of the Ba:Ti ratio is also obtained, which is of great technological interest as dielectric ageing as well as other dielectric properties strongly depend on it. LTAS can also be used to produce ferroelectric materials with controlled composition, introducing suitable homogeneously dispersed additives and dopants which modify the dielectric characteristics according to the user's requirements .
High Entropy Oxide Phases with Perovskite Structure
Nanomaterials
The possibility of the formation of high entropy single-phase perovskites using solid-state sintering was investigated. The BaO–SrO–CaO–MgO–PbO–TiO2, BaO–SrO–CaO–MgO–PbO–Fe2O3 and Na2O–K2O–CaO–La2O3–Ce2O3–TiO2 oxide systems were investigated. The optimal synthesis temperature is found between 1150 and 1400 °C, at which the microcrystalline single phase with perovskite structure was produced. The morphology, chemical composition, crystal parameters and dielectric properties were studied and compared with that of pure BaTiO3. According to the EDX data, the single-phase product has a formula of Na0.30K0.07Ca0.24La0.18Ce0.21TiO3 and a cubic structure.
Hydrothermal synthesis of perovskite and pyrochlore powders of potassium tantalate
Journal of Materials Research, 2002
Potassium tantalate powders were hydrothermally synthesized at 100 to 200 °C in 4 to 15 M aqueous KOH solutions. A defect pyrochlore, Kta2O5(OH). nH2O (n ≈ 1.4), was obtained at 4 M KOH, but at 7–12 M KOH, this pyrochlore was gradually replaced by a defect perovskite as the stable phase. At 15 M KOH, there was no intermediate pyrochlore, only a defect perovskite, 0.85Ta0.92O2.43(OH)0.57 0.15H2O. Synthesis at higher KOH concentrations led to greater incorporation of protons in the perovskite structures. The potassium vacancies required for charge compensation of incorporated protons could accommodate water molecules in the perovskite structure.
Hydrothermal synthesis of perovskite based materials for microelectronic applications
2000
The hydrothermal technique was used as a perspective method to synthesize barium strontium titanate (BST) bulk materials with nanocrystalline structure. X-ray diffraction, SEM/EDS and dielectric measurements were performed on BST sintered pellets. The results thus obtained are of interest for the optimization of the manufacturing process of perovskite bulk ceramics by controlling synthesis parameters (concentration, temperature, time) and sintering temperature.
Solid State Ionics, 2018
Hydration-dehydration cycles are critical to the mechanical performance of ceramic proton conductors. The development of in situ methods is desirable in order to study their structural response under conditions that mimic the operating ones. Neutron powder diffraction studies combined with simultaneous thermogravimetric analysis were performed on the hydrated forms of two members of the oxygen deficient perovskite BaTi 1-x Sc x O 3-δ series, with x = 0.5 and x = 0.7. Rietveld analyses agreed with in situ gravimetric data, allowing correlation of occupancy factors of the oxygen site to hydration levels and other structural data. Dehydration is an activated process that impacts on structural parameters and the level of Sc substitution was found to control the structural response during in situ dehydration, with higher Sc content leading to significantly greater volume contraction. This was rationalised by the chemical expansion due to hydration of oxygen vacancies within the x = 0.5 sample being anomalously small. Furthermore, the behaviour of the x = 0.5 system revealed an unexpected cell expansion during the early stages of dehydration, suggesting the hydration level may influence the thermal expansion coefficient (TEC).
Further physicochemical studies on aid-sintered and modified perovskite-type ceramics
Materials Letters, 2003
Double A,B-doped and aid-sintered BaTiO 3 perovskite ceramics were prepared by usual ceramic techniques and firing procedure. On pellets of these potential materials, numerous measurements have been undertaken, explained and discussed in detail, namely, X-ray diffraction, IR absorption spectra, electronic absorption spectra and dc electronic conductivity versus temperature in ambient atmosphere. New information was added and supported which are benefit and helpful in modifying the crystallinity and semiconductivity of the potential perovskite ceramics. D
Formation and stability of non-toxic perovskite precursor
Langmuir, 2019
Strontium, calcium, and magnesium silicate hydrate phases are synthesized by the reaction between silica and solution of metal hydroxides. The kinetics of the reaction is recorded using a quartz crystal microbalance (QCM), continuously monitoring the change in frequency and dissipation energy. Based on QCM results, it is shown that properties of solutions like the pH-value or the type of ions play a pivotal function on the ratedetermining stage of the reaction, the thickness of the diffuse layer, the formation of carbonates as well as the kinetics of the formed phases. Further properties of the reaction products are investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and infrared spectroscopy (IR). With the help of thermogravimetric analysis (TGA) and temperature-dependent X-ray diffraction (XRD), we investigate how our synthesized phases can be turned into MSiO 3 structures. Finally, the Goldschmidt rules for perovskites structures show that this might be an attractive way for new and non-toxic phases in the future.
Thermodynamics of Nanoscale Calcium and Strontium Titanate Perovskites
The surface enthalpies of nanocrystalline CaTiO3 and SrTiO3 perovskites were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calo- rimetry. The nanocrystalline samples were synthesized by a hydrothermal method and characterized using powder X-ray dif- fraction, FTIR spectroscopy, and Brunauer–Emmett–Teller sur- face area measurements. The integral heats of water vapor adsorption on the surfaces of nanocrystalline CaTiO3 and SrTiO3 are 78.63 ` 4.71 kJ/mol and 69.97 ` 4.43 kJ/mol, respectively. The energies of the hydrous and anhydrous surfaces are 2.49 ` 0.12 J/m2 and 2.79 ` 0.13 J/m2 for CaTiO3 and 2.55 ` 0.15 J/m2 and 2.85 ` 0.15 J/m2 for SrTiO3, respectively. The stability of the perovskite compounds in this study is discussed according to the lattice energy and tolerance factor approach. The energetics of different perovsk- ites suggest that the formation enthalpy becomes more exother- mic and surface energy increases with an increase in ionic radius of the “A” site cation (Ca, Sr, and Ba), or with the tol- erance factor. PbTiO3 shows a lower surface energy, weaker water binding, and a less exothermic enthalpy of formation than the alkaline-earth perovskites.