Nanocrystalline Zn2SnO4 powders doped with Eu3+ ions were synthesized via a mechanochemical solid-state reaction method followed by postannealing in air at 1200 °C. X-ray diffraction (XRD), ...energy-dispersive X-ray (EDX), and Raman and photoluminescence (PL) spectroscopies provide convincing evidence for the incorporation of Eu3+ ions into the host matrix on noncentrosymmetric sites of the cubic inverse spinel lattice. Microstructural analysis shows that the crystalline grain size decreases with the addition of Eu3+. Formation of a nanocrystalline Eu2Sn2O7 secondary phase is also observed. Luminescence spectra of Eu3+-doped samples show several emissions, including narrow-band magnetic dipole emission at 595 nm and electric dipole emission at 615 nm of the Eu3+ ions. Excitation spectra and lifetime measurements suggest that Eu3+ ions are incorporated at only one symmetry site. According to the crystal field theory, it is assumed that Eu3+ ions participate at octahedral sites of Zn2+ or Sn4+ under a weak crystal field, rather than at the tetrahedral sites of Zn2+, because of the high octahedral stabilization energy for Eu3+. Activation of symmetry forbidden (IR-active and silent) modes is observed in the Raman scattering spectra of both pure and doped samples, indicating a disorder of the cation sublattice of Zn2SnO4 nanocrystallites. These results were further supported by the first principle lattice dynamics calculations. The spinel-type Zn2SnO4 shows effectiveness in hosting Eu3+ ions, which could be used as a prospective green/red emitter. This work also illustrates how sustainable and simple preparation methods could be used for effective engineering of material properties.
In the last decades, water pollution from different industries has been one of the largest environmental issues. Many efforts have been made to develop technologies to remove toxic pollutants from ...the contaminated waters, which are direct threats to the aquatic environment and human health. Among different technologies, heterogeneous catalysis has shown to be very effective for water purification. The main issue regarding this method is the water recovery after the treatment, which is a very expensive and laborious procedure but can be addressed by the immobilization of photocatalytic particles on the support material. Here, we present efficient and green technology for water purification based on ZnO/SnO2-poly(methyl methacrylate) (PMMA) nanocomposite foils utilizing superior photocatalytic properties of coupled ZnO and SnO2 photocatalysts. We investigated the influence of the ZnO/SnO2 nanoparticle concentration on the removal efficiency of methylene blue dye and found exceptional removal efficiency for even very low ZnO/SnO2 nanoparticle loadings. The investigated foils were found to be highly reusable, with no change in performance after five successive usages. The composition, optical properties, surface morphology, and surface roughness of the foils were characterized by X-ray diffraction, UV–vis spectroscopy, scanning electron microscopy, and atomic force microscopy. The thermal measurements performed with differential scanning calorimetry suggested the reinforcement effect of ZnO/SnO2 nanoparticles on the PMMA matrix, which is essential for practical applications of the foils.
In this study, dielectric and bipolar resistive switching properties of the chalcogenide from the Ag–As40S30Se30 system were investigated for potential application in non-volatile memory devices. ...Preparation of the glasses was done with the use of melt-quenching technique. Current–voltage (I–V) characteristics were determined at different temperatures, and stability of the Ag/chalcogenide sample/Ag structure through constant value of memory window was noticed. Namely, it was observed that a bipolar resistive switching effect is present in the prepared samples with noticeable transitions between high-resistance and low-resistance states when the voltage polarity was changed. Temperature dependent I–V measurements indicated that resistive switching voltage decreases as temperature increases suggesting thermally activated motion of charge carriers. The conduction model fitting results suggested that the Ohmic and space-charge limited current conduction are responsible for resistive switch. Based on the analysis of the obtained results, resistive switching mechanism was explained by using filamentary conduction. In addition, study of dielectrical properties indicated presence of space charge polarization. The presented results show that the synthesized material has properties that suggest them for potential application in non-volatile memory devices.
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•Ag-doped As–S–Se chalcogenide manifest bipolar resistive switching effect.•At all temperatures, the ratio of OFF and ON state resistance are constant.•Ohmic and SCLC are responsible for resistive switch.•Dielectric properties indicated presence of space charge polarization.
•Influence of Ag in As-S-Se on physical and topological properties has been analyzed.•Structural and morphological properties were investigated by XRD, EDS and SEM.•Compositional dependence on ...resistive switching properties is studied.•Resistive switching voltage decreases with silver concentrations.•Studied samples show good memristive characteristics.
Physical properties of quaternary chalcogenide Agx(As40S30Se30)100-x, glasses were analyzed. Synthesis of the studied samples x = 6 - 9 at.% Ag was performed by melt quenching in cascade regime of heating. X-ray diffraction analysis verified amorphous character of the synthesized samples. Morphological characterization was carried out using a scanning electron microscopy, and energy-dispersive X-ray mapping. The obtained results show that the density of the system increases upon silver incorporation in the glassy As40S30Se30 matrix, which is manifested through decrease of free volume percentage. Assessment of various physical and topological properties of prepared series of chalcogenide materials was done using theoretical models available in the literature. Specifically, compactness, average coordination number, constraint parameters, cross-linking density, floppy modes, number of lone–pair electrons are analyzed with addition of Ag atoms in the As40S30Se30 matrix. Average single bond energy and the mean bond energy were also discussed. The chemical bond approach model was used to study the cohesive energy of the studied Ag-containing As-S-Se samples. It is found that all studied parameters are dependent upon silver concentrations. Finally, the room-temperature memristive characteristics and compositional dependence on resistive switching properties in a wide range of Ag concentrations were examined in this paper.
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of Electrochemical Impedance Spectroscopy (EIS) are reported for lithium-niobium-titanium-oxide (LNTO) ceramics synthesized by a solid-state reaction method with two functional additives (MoO3 or ...ZnO) in the temperature range 323 K - 573 K and frequencies between 10−1 Hz and 107 Hz. Scanning electron microscopy (SEM) reveals a textured morphology of rod and plate-like particles that are typical for M-phase LNTO materials, while X-ray diffraction (XRD) analysis confirms the formation of an M-phase member compound with an approximate structure of Li7Nb3Ti5O21. Complex impedance analysis indicates that its overall electrical resistivity behavior depends mostly on the grain boundary processes. EIS analysis shows a negative temperature coefficient of resistance behavior (NTCR) in a defined temperature range in two LNTOs and thermal activation of the conduction mechanisms. The low dielectric constants of 5.5 and 12.1 at 1 MHz were found for the first and second LNTOs, respectively. Complimentary Raman spectroscopic measurements, despite very large crystallographic unit cell of LNTO, reveal only a small number of lines, which is the consequence of a “molecular” nature of materials.
•Crystallization of the glasses takes place as a one- or two dimensional growth.•A dominant role in crystallization of glass samples play already present centers.•Variation of crystallization ...activation energy with χ indicate process complexity.•Thermal stability of all compounds decreases with increase in antimony content.•Compounds with optimum crystallization affinity are in the range of x = 50–70 at.%.
This paper presents the results of non-isothermal kinetics of crystallization processes in complex amorphous chalcogenide glassy system (As2Se3)100−x(SbSI)x (x = 20, 30, 50, 70 and 80 at.%). The results were obtained using differential scanning calorimetry in non-isothermal regime of work at different heating rates. The crystal growth kinetics was determined by application of several isokinetic and isoconversional theoretical models on experimental data. Kinetic parameters, such as activation energy of crystallization E and the Avrami exponent n have also been determined. It was established that parameter E depends on degree of conversion. The values of Avrami exponent indicated that crystallization mechanism is one-dimensional and nucleation takes place at the surface in the samples with lower SbSI content. For the compositions with higher SbSI amount crystallization process is realized as a volume nucleation. Also, there is an increase in devitrification affinity with the greater presence of structural units of the type Sb2S3 and SbSI, instead of Sb2Se3 and As2Se3. The decrease in thermal stability for the samples with x = 70 and 80 at.% was also noted and confirmed with several parameters using different criteria.
A new titanium/molybdenum/mixed-oxides (TMO) contact-type heterojunction photocatalyst was prepared by a simple, low-cost, and environmentally-friendly mixing-calcination solid-state method. A ...microstructural investigation by scanning electron microscopy (SEM) showsirregularly shaped agglomerated morphology of TMO that consists of firmly connected globular TiO2 and rod-like MoO3 particles. The detailed structure and optical bandgap investigation by X-ray diffraction, Raman, and UV-Vis spectroscopy revealed the TMO’s composition of ~37 wt.% rutile TiO2, ~25 wt.% of anatase TiO2, and ~38 wt.% of molybdite MoO3 phase and an absorption threshold of around 380 nm, which implies more probability of desirable higher visible light absorption. The removal efficiency of pesticides quinmerac (QUI) and tembotrione (TEM), and pharmaceuticals metoprolol (MET), amitriptyline (AMI), ciprofloxacin (CIP),and ceftriaxone (CEF) from water in the presence of starting pure TiO2, MoO3, and prepared TMO were investigated under different pH values and UV irradiation/simulated sunlight (SS). Each starting metal-oxide precursors and prepared TMO showed a different affinity for adsorption of tested pesticides and pharmaceuticals, and, in general, better photocatalytic degradation efficiency under UV irradiation than under simulated sunlight. The highest photocatalytic degradation efficiency under UV irradiation was 81.6% for TEM using TMO; using TiO2 was 65.0% for AMI, and using MoO3 was 79.3% for CEF after 135 min. However, TMO showed a very high synergic adsorption/photocatalytic under-SS efficiency in the removal of CIP of almost 80% and under UV irradiation of 90% CIP removal after 75 min. The toxicity of catalysts, starting compounds, and their intermediates formed during the removal process was assessed using a rat hepatoma cell line (H-4-II-E). The highest hepatotoxic effects were obtained by using UV irradiated QUI and MET suspension with TMO for up to 60 min.
Er and Er,Yb-activated zinc-tin-oxide-based phosphors are synthesized for the first time by a mechanochemical solid-state method. Several techniques, including X-ray diffraction (XRD), Raman, and ...photoluminescence (PL) spectroscopy are used for structure and optical investigation. Morphology analysis by scanning electron microscopy (SEM) shows agglomerates of non-uniform in size and shape particles. XRD analysis confirms the major inverse spinel Zn2SnO4 phase formation with high crystallinity. Luminescence activation by Er3+ upon 980 nm excitation leads to green emissions centered at 532 nm and 551 nm and a narrow-band red emission centered at 654 nm that double increases by Yb3+ ions cooperative sensitization.
We report on the dynamics of the softening process of Bi
6
(As
2
S
3
)
94
through studying the AC impedance response in the frequency interval of 1 Hz to 10 MHz at operating temperatures of ...323–373 K. The increase of glass fictive temperature with heating rate, observed in DSC curves, is explained using the Lasocka equation. The analysis of impedance spectra indicated single-phase glass behavior for Bi
6
(As
2
S
3
)
94
, whereas the appearance of internal interfaces was confirmed for Bi
7
(As
2
S
3
)
93
at all temperatures. While this was previously assigned to the boundary surface of the matrix–interface region and the crystalline centers themselves, the extension of the observed range now revealed that at low temperatures, amorphous phase separation without crystal precipitation comes into play. By analyzing the impedance data, we determined refined DC resistance and relaxation time values, and also confirmed the decrease of resistance with temperature for both compositions. Similar activation barriers for α relaxation and charge carrier mobility indicate that both processes are strongly coupled. The
I
–
V
characteristics of the Bi
7
(As
2
S
3
)
93
sample recorded up to
T
= 373 K show bipolar resistive switching behavior controlled by voltage. At higher temperatures, there is switching with conducting filament due to the contribution of crystalline centers.
The work is concerned with the effect of copper content on electrical conductivity of the bulk amorphous semiconducting glasses from the system Cu
x
(As
2Se
3)
0.9(AsI
3)
0.1
100
−
x
(
x
=
0, 1, 5 ...and 10
at.% Cu). The DC conductivity, measured in the temperature range of 300–420
K, shows a semiconducting behaviour of the Arrhenius-type. The AC conductivity was measured in the frequency range of 10
2–10
6
Hz in the temperature interval from 298 to 398
K. Results indicate that the increase of copper content yields a significant increase of the conductivity and a lower activation energy. Dominant conduction mechanisms are the transfer of charge carriers between localized states at the band edges (band tails) and hopping between localized states near the Fermi level. The decreasing temperature dependence of the exponent
s points out to the correlated barrier hopping conductivity mechanism.
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