For the first time, it was demonstrated that the catalytic properties of semiconductors can be activated using an external electric field only. More particularly, the TiO2 and Fe2O3 were found to ...produce noticeable amounts of carbon monoxide from carbon dioxide – water vapor gas mixture under the electric field with the strength in the 104 V/cm range. The reported process, i.e. the activation of semiconductors using the electric field is more efficient than the utilization of UV–vis radiation in terms of energy efficiency and amount of products formed.
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•Catalytic properties of semiconductors was activated using the external electric field only.•Wet CO2 was converted into CO over TiO2 and Fe2O3 in the presence of field in the 104 V/cm range.•The activity of investigated semiconductors depended on both surface and electronical properties.
In present work, two types of substrates for the surface enhanced Raman scattering (SERS) spectroscopy based on silver-coated porous silicon (por-Si) and HfO
x
/por-Si are engineered. The por-Si ...samples are formed by electrochemical etching the monocrystalline silicon and have a mean pore diameter of 850 nm and a porous layer thickness of 5 µm. Deposition of the hafnium oxide film on the por-Si surface is performed by atomic layer technique, while the SERS-active silver particles are grown by the chemical “silver mirror” method. The HfO
x
-free substrates demonstrate better SERS-activity but result in changes of the analyte molecule (Ellman’s reagent) spectra, which is supposed to associate with their thermal degradation. Oppositely, the Ag/HfO
x
/por-Si samples provide sufficient and stable enough SERS-activity during at least 1-min SERS-measurements. We assume the observed stability of the analyte on the substrates containing HfO
x
can be caused by the faster heat dissipation from the laser spot due to more uniform and conformal silver coating than that on HfO
x
-free sample. The conformal deposition of silver is provided by passivation of the por-Si surface with auxiliary HfO
x
layer. An analytical enhancement factor for the Ag/HfO
x
/por-Si substrate equals to 2·10
3
. Therefore, the SERS-active substrate containing HfO
x
provided athermal effect on analyte.
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•Ca/Ti and Ca/Nb substitutions modify the antiferromagnetic structure of BiFeO3.•The cycloidal structure → canted structure transformation is studied.•Lattice defects contribute to ...the instability of the cycloidal antiferromagnetic order.
Herein, we report on the crystal structure, magnetic and local ferroelectric properties of the Bi1−xCaxFe1−xTixO3 and Bi1−xCaxFe1−x/2Nbx/2O3 perovskites prepared by a solid state reaction method. It has been found that the Ca2+/Nb5+-containing series is characterized by a narrower concentration range (x ≤ 0.2) over which the acentric R3c structure specific to the pure BiFeO3 can be stabilized. The compositional variation in the critical concentration defining the polar/nonpolar (R3c/Pnma) phase boundary can be understood as related to the chemical modification-induced changes in the lattice spacing diminishing the stability of the a−a−a− tilting in favor of the a−b+a− one. Both the Ca2+/Ti4+ and Ca2+/Nb5+ substitutions ensure the suppression of a cycloidal antiferromagnetic order, thus leading to the formation of a weak ferromagnetic polar state. While this effect is proven to be associated with a composition-driven reduction in polar displacements, lattice defects are supposed to contribute to the instability of the cycloidal spin arrangement.
•High-temperature neutron diffraction study of Ca/Ti- and Ba/Ti-doped BiFeO3 was performed.•The heating-induced R3c ↔ Pnma (Ca/Ti) and R3c ↔ Pm3-m (Ba/Ti) phase transitions were revealed.•The ...temperature-driven changes in structural parameters of the ferroelectric phase were described.
The structural parameters of the Bi0.85AE0.15Fe0.85Ti0.15O3 (AE = Ca and Ba) multiferroics have been determined using variable temperature neutron powder diffraction. The compounds adopt the polar rhombohedral R3c structure near room temperature and undergo phase transitions into either the nonpolar orthorhombic Pnma (AE = Ca) or cubic Pm3-m (AE = Ba) structures on heating. In the ferroelectric phase, a temperature-driven lattice expansion is accompanied by both a diminishing of the off-center ionic displacements (thus resulting in a decrease in the spontaneous electric polarization) and a reduction in the magnitude of the antiphase oxygen octahedra tilting. Being largely different for the materials under study, the latter parameter is supposed to specify the dissimilarity in their magnetic properties.
The molecular arrangement and phase transitions in the vanadyl hexadecafluorophthalocyanine (VOPcF16) thin films grown by physical vapor deposition have been studied using in situ X-ray diffraction, ...atomic force microscopy, and optical spectroscopy techniques (UV, IR, and Raman). The complete transition from the low-temperature linear cofacial structure to the slipped dimeric one occurs in the temperature range 160–220 °C. This conversion was found to be irreversible upon cooling the VOPcF16 film back to 20 °C. The structural transformation leads to decrease of the in-plane conductivity of the film by 2 orders of magnitude. According to the polarized Raman spectroscopy measurements, the mean tilt angles between the VOPcF16 species and the substrate surface were 59 ± 5° and 30 ± 5° in the as-deposited and annealed films, respectively. For the sake of comparison, the structure of the thin films of vanadyl phthalocyanine (VOPc) was also studied. The mean tilt angle between the VOPc species and the substrate surface was found to be 77 ± 5°, in good agreement with existing experimental data (∼70°). All intense bands in the experimental IR and Raman spectra of VOPcF16 and VOPc were assigned using DFT calculations (B3LYP) and the 15N isotopic shifts in the vibrational spectra of VOPc.
•Ca/Nb doping can be used to modify the cycloidal antiferromagnetic structure of BiFeO3.•As a result, a weak ferromagnetic ferroelectric state can be stabilized.•The magnetic transformation is driven ...by a doping-induced reduction of electric polarization.•Lattice defects contribute to the instability of the cycloidal antiferromagnetic order.
In this paper, we report on the crystal structure, magnetic and local ferroelectric properties of the Bi1−xCaxFe1−x/2Nbx/2O3 (x ≤ 0.2) compounds prepared by a solid state reaction method. The chemical substitution has been found to reduce the polar ionic displacements in the acentric R3c structure and give rise to the formation of the non-polar Pnma phase at x = 0.2. The substitution-driven decrease of spontaneous polarization is accompanied by the suppression of the cycloidal antiferromagnetic order specific to the parent BiFeO3. As a result, a weak ferromagnetic and ferroelectric state is formed at x ≈ 0.18. Lattice defects contribute to the instability of the cycloidal structure, thus providing the antiferromagnetic + weak ferromagnetic phase coexistence observed over a wide range of Ca/Nb concentrations.
This work justifies the practical importance of corrosion and erosion resistance of refractories during the design of direct electric heating furnaces used for the vitrification of high-level waste ...(HLW). The major promising materials are listed, and an algorithm for assessing their resistance to borosilicate melts during the electric furnace operation is provided. Corrosion testing of the refractories was performed in static and dynamic conditions in a low-melting borosilicate glass melt with and without simulated liquid HLW. Refractory materials were selected with the highest resistance in conditions mimicking a glass melt containing solidifying HLW. The results will be used to guide the choice of the lining material during the design of removable and small-scale melters.
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Integrated field-emission devices and integrated circuits (ICs) based on them are a promising direction in microelectronics, which is associated with the use of low-voltage and stable field ...emitters based on nanomaterials, such as carbon nanotubes (CNTs). The planar design of the field-emission device makes it possible to form CNTs at the end of a thin catalyst film 1–50 nm thick. The paper presents the results of the implementation of an integrated technology for manufacturing planar field-emission diodes with a CNT cathode formed at the end of a thin conducting film. The CNTs are grown by chemical-vapor deposition. A thin film of initially amorphous Co–Nb–N–(O) alloy is used as the growth catalyst. A feature of the technology is the crystallization of Co–Nb–N–(O) alloy during heating in the process of chemical-vapor deposition. As a result, Co nanoparticles are formed on the alloy surface, which catalyze the growth of CNTs. It is shown that this specific feature makes it possible to form CNTs locally, only in open areas of the Co–Nb–N–(O) alloy, for example, at the ends of a thin film. The choice of the Co–Nb–N–(O) alloy is substantiated. The stages of formation of planar field-emission diodes on a silicon substrate are described using standard manufacturing processes. The results of measuring the
I
–
V
characteristics of devices are presented. It is shown that the type of
I
–
V
characteristics is determined by the field emission characteristic of CNTs. The developed technological method for the local synthesis of CNTs at the ends of topologically formed regions of a thin Co–Nb–N–(O) alloy film can be incorporated into an integrated technology for the formation of planar field-emission devices.
This paper presents the results of facile fabrication of a non-enzymatic glucose sensor by forming a sensing element based on TiO2 nanofilaments using direct ink writing (DIW). The glucose ...concentration in the solution was determined by changing the resistance of the TiO2 layer. Nanowires (NW) were obtained by hydrothermal synthesis in 10 M sodium alkali solution followed by heat treatment. The surface morphology of obtained samples was studied using scanning electron microscopy. The formation of a sensitive layer was carried out on a 3D printer with a specially designed print head from a suspension based on an aqueous solution of polyvinyl alcohol (PVA) followed by heat treatment in air. The suspension was analyzed for viscosity and contact angle. The sensitive layers were formed on a silicon substrate with a SiO2 surface oxide layer and gold contacts. Layers of TiO2 NW were formed between the contacts. The sensitivity of the sensor to glucose solutions of various concentrations was studied. As a result of the studies, the studied structures showed sensitivity to a glucose solution in the range from 1 to 100 mmol.
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