Using Raman spectroscopy, the study of a polymorphic phase transition in the KNNLiTaLa
0.01
compound is presented. An analysis of the behavior with temperature, wavenumber and half width at full ...maximum of the individual bands, corresponding to the vibration modes of the (Nb/Ta)O
6
octahedra of the KNNLiTaLa
0.01
compound's structure, is performed. This analysis determined that the polymorphic phase transition of the KNNLiTaLa
0.01
compound occurs in the 90 to 105°C temperature interval. Using the Hard Mode Spectroscopy method, the value of the critical exponent of the order parameter was determined to be β ≈ ½, indicative of a second order transition.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•Pt/CNT/TiO2 electrocatalyst was successfully prepared by the sonochemical method.•The electrocatalyst Pt/CNT/TiO2 was synthesized without heat treatments, additives or surfactants.•The TiO2-Pt ...interaction improves the CO-tolerance of Pt/CNT/TiO2, as well as the electrocatalyst stability.•Low amount of multi-walled carbon nanotubes increases the current density of Pt/CNT/TiO2 significantly compared to Pt/TiO2.
Pt electrocatalyst supported on composite formed of multi-walled carbon nanotubes and titanium oxide (CNT/TiO2) was successfully synthesized by a sonochemical method without heat treatments, surfactants or additives. This electrocatalyst could be used for direct methanol fuel cells (DMFC) applications. For comparison, Pt/CNT and Pt/TiO2 electrocatalysts were prepared as reference samples. Structural properties and morphology of the synthesized materials were examined by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and their specific surface areas were determined by the Brunauer-Emmett-Teller method. The Pt and acid-treated CNT contents were analyzed by inductively coupled plasma atomic emission spectroscopy and thermogravimetric analysis, respectively. The electrochemical properties of the synthesized electrocatalysts were evaluated by cyclic voltammetry (CV) and chronoamperometry in a three-electrode cell at room temperature. The evaluation performed using electrochemical techniques suggests that TiO2 promotes the CO-tolerance due to TiO2-Pt interaction. The CV tests demonstrated that 6wt.% of acid-treated CNT increases significantly the current density when Pt selectively interacts with TiO2.
A structural and physical properties study on ferroelectric (K0·44Na0·52Li0.04)0.97La0·01Nb0·9Ta0·1O3 ceramics with monocrystalline grains of orthorhombic (O) and tetragonal (T) perovskite phases ...coexisting at room temperature (RT) is presented. Different sintering temperatures were evaluated. XRD analysis demonstrates high crystalline quality of both phases with volume fractions depending of the sintering temperature. SEM shows grain facets and morphologies of both phases in all samples. Raman analysis confirms the dopant incorporation and the coexistence of both phases. The contributions of each phase in the dielectric response are deconvoluted using the frequency-temperature dielectric analysis. The orthorhombic-to-tetragonal (TO-T) and tetragonal-to-cubic (TT-C) phase transition temperatures shift ~100 °C below those reported for pure-KNN in all samples, as consequence of the Li, La, and Ta doping combination. Li doping promotes T-phase grain growth and decreases TO-T below RT. La incorporation promotes the O-phase grain growth and decreases TO-T and TT-C. The optimal sintering temperature is 1180 °C with 50-50 volume fractions of T-O phases. Piezoresponse studies show a complex 180°-domain structure.
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•Lead free Li/La doped KNNTa ceramic is constituted by coexisting tetragonal and orthorhombic structured grains.•Li doping promotes tetragonal grain growth and La incorporation promotes the orthorhombic grain growth.•Li and La combination shifts the FE-FE transition below room temperature.•The coexistence of two phases provides better room temperature functionality for applications.
This work presents a study of ceramics with the (K0.44Na0.52Li0.04)0.97La0.01Nb0.9Ta0.1O3 composition through their Raman spectra. In the previous studies 1, this particular composition has shown ...good permittivity and piezoelectric parameter values that justify a deeper investigation. Two sets of samples of these ceramic compounds were prepared using different methods. The first set was prepared using a classical solid-state reaction of oxides and carbonates, as described in Ref. 2. The second set was prepared using the NaNbO3 as a precursor. The Raman spectra of the samples obtained by the direct ceramic method consisted of 4 modes. In contrast, the spectra of the samples obtained using the precursor showed a shift of the wavenumber of the A1g(ν1) mode peak towards lower values and consisted of six modes with the appearance of two additional IR modes, F1u(ν3) and F2g(ν4). Notably, the use of the precursor preparation route led to important improvements resulting in a more straightforward method than that of Saito et al. 3.
In the current study, a new approach to the synthesis of highly destacked ReS2 layers embedded in amorphous carbon via the thermal decomposition of a tetraoctylammonium perrhenate precursor, under ...sulfidizing atmosphere (15% v/v H2S mixture H2S/H2 gas), is described. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analysis of the thermolysis product confirm the formation of rhenium disulfide. The synthesized compound is found as single layers with a minor proportion of few-layer arrangements, embedded in amorphous carbon. X-ray diffraction, UV–visible diffuse reflectance, and thermogravimetry analysis were made in order to characterize the metal-organic salt precursor, showing that the perrhenate ions are dispersed widely from each other in the matrix of the organic cations, forming an inorganic-organic salt. The special arrangement of these ReS2 layers has a potential use as a heterogeneous catalyst due to the high proportion of edge sites.
•Highly destacked ReS2 layers embedded in amorphous carbon were synthesized.•The novel synthesis involved the sulfidization of an (Oct4N)ReO4 precursor.•Amorphous carbon act as a structural stabilizer in the final composite.
