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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 pyroelectric properties of polyvinylidene fluoride/trifluoroethylene doped with graphene oxide were studied. The pyroelectric current measurements were performed for polarized and non-polarized ...samples with different amount graphene oxide: 5, 10, 15, 20, 25%. The polarization process influence on pyroelectric current was discussed. Moreover the impact of different amount of dopant on pyroelectric properties of polyvinylidene fluoride/trifluoroethylene was analyzed. On the basis of obtained results the phase diagram was performed.
•The pyroelectric current measurements of P(VDF-TrFE) (70%–30%) doped with grapheme oxide were performed.•The model of structure of P(VDF-TrFE) doped with GO proposed in https://doi.org/10.1016/j.polymertesting.2017.04.003 was confirmed.•The phase diagram of P(VDF-TrFE)-GO was performed. The morphotropic phase boundary has been predefined.
The reaction of tyre rubber crumb with nitrous oxide (N2O) in an organic solvent at 180–230 °C and pressure of 3–5 MPa was studied. The process is accompanied by controllable destruction of ...vulcanised rubber with the formation of a plastic reclaim product consisting of a sol and gel fractions. The amount of the sol fraction increases proportionally to the conversion of the rubber CC bonds in the reaction with N2O and can be regarded as a measure of the degree of vulcanisate destruction. The method is applicable to the recycling of both rubber crumb and tyre chips.
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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 work is concerned with developing an approach to producing an array of plasmonic Ag nanoparticles on the nanopipette surface. The vacuum thermal evaporation method followed by annealing was used ...to form the nanoparticle array. The surface morphology of the modified pipettes was investigated by scanning electron microscopy. Based on the SEM images obtained, the most efficient method for particle deposition on the pipette was selected. It was found that two-stage depositions on the horizontally mounted pipette formed an array of silver nanoparticles with a size of about 16 nm. The obtained modified nanopipettes were investigated by Raman spectroscopy. A laser with a wavelength of 532 nm was used to obtain the spectra. Rhodamine in the R6G modification was used as an analytical substance. The enhance factor of the modified pipette was calculated by comparing it with pure glass at the same power values of the laser and concentration of the analytical substance, rhodamine R6G. The developed approach to modifying the surface of nanopipettes allows fabricating SERS pipettes for monitoring various intracellular biomarkers.
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.
Abstract
This work shows the possibility of forming a planar diode structure based on carbon nanotubes formed on a catalytic alloy film Co-Nb-N-(O). The paper presents a technological route for the ...formation of a planar diode structure Si/SiO
2
/Si
3
N
4
/Co-Nb-N-(O)/SiO
2
and studies the emission characteristics. The current-voltage characteristic of the obtained diode structure in the Fowler-Nordheim coordinates is close to linear in the range from 15 to 22 V, which confirms the phenomenon of electron emission.
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