Volume 91, Issue 11

Speciation and location of Co 2+ , Mn 2+ and Ni 2+ in the extraframework positions of the dehydrated zeolite matrix of ferrierite structure were studied in detail using FTIR spectroscopy of antisymmetric T–O–T vibrations of the zeolite framework. Me 2+ –ferrierites were prepared by the ion exchange of the NH 4 – and Na–zeolite forms and by impregnation of the NH 4 form. Bare Me 2+ occupies all three known cationic sites in dehydrated cationic zeolite. The wavenumbers of bands of individual cations in individual sites were identified. At low Me 2+ loadings (Me 2+ /Al < 0.15), Me 2+ replaces two protonic sites and exclusively bare Me 2+ is present in dehydrated samples. Sets of such samples were employed for the estimation of extinction coefficients of Co 2+ , Mn 2+ and Ni 2+ in cationic sites. These coefficients differ for individual cations but are the same for a cation at different sites. Ion exchange to the NH 4 form allows preparation of samples with maximum possible loading of bare Me 2+ only for Co 2+ . In the case of Mn 2+ , exchange to the Na-parent zeolite or impregnation is required for this purpose while samples with maximum loading by bare Ni 2+ can be prepared only by impregnation.

This paper reports an original nonstandard green concept to obtain TiO 2 microrods with polyhedral densely stacked 3D nanovoids prepared via the heat treatment of a hydrogen titanate. The intermediate hydrogen titanate was synthesized by a solid-liquid-solid (SLS) route from an ammonia-saturated aqueous solution of TiOSO 4 at 0 °C. The effect of the postgrowth thermal annealing procedure to remove ice (water) and the proposed mechanism to explain the underlying transitions from the intermediate precursor to nanostructured TiO 2 microrods with stacked 3D nanovoids were investigated. The small-angle X-ray scattering (SAXS) analysis indicates that at temperatures above 500 °C, the release of confined ice (water) takes place, which leads to the creation of self-assembled polyhedral nanovoids open to the surface. Their size ranges from 5 to 78 nm in both length and width, with a depth of ~3.88 nm. The first use of these stacked 1D TiO 2 microrods as the working electrode in a photoelectrochemical (PEC) cell for water splitting is demonstrated. The estimated value of ζ-potential depends on both annealing temperature and crystallite size. Anatase sample 1D TiO/800 with ζ-potential (−29.1) mV and average crystallite size ~68 nm was observed to be highly stable in aqueous suspension. The SLS method yields low-cost 1D TiO 2 materials possessing high photoreactivity with water. The PEC measurements indicate that three-dimensional hollow structures with a controlled geometry via patterned 1D TiO 2 surface are promising materials for hydrogen generation from water splitting.

Raman spectroscopy has a long-standing reputation as a powerful tool for structural investigation of the various materials. However, application of this technique to study the melt structure directly under high-temperature requires its certain modification. The methods of the registration of high-temperature Raman spectra were considered. Particular attention was paid to considering the systems on time-resolved filtering of the thermal radiation.

The paper reports on ≈1.5 μm Stokes photoluminescence (PL) emission and upconversion photoluminescence (UCPL) emission in the visible and near-infrared spectral region in Er 3+ -doped Ge 25 Ga 8 As 2 S 65 chalcogenide glasses at pumping wavelengths of 980 and 1550 nm. The ≈1.5 μm PL emission spectra are broadened with increasing concentration of Er ions which is discussed in terms of radiation trapping and UCPL dynamics affecting the Er 3+ : 4 I 13/2 level lifetime. The UCPL emission was observed at ≈530, ≈550, ≈660, ≈810 and ≈990 nm and its overall intensity as well as red-to-green UCPL emission intensity ratio increases with increasing Er concentration. To explore the UCPL dynamics we measured double logarithmic dependency of green (≈550 nm) and red (≈660 nm) UCPL emission versus pump power at pumping wavelength of 975 nm. Moreover, we measured quadrature frequency resolved spectroscopy (QFRS) on green UCPL emission (≈550 nm) using 975 nm pumping wavelength and various excitation powers. The QFRS spectra on green UCPL were analyzed in term of QFRS transfer function for three-level model from which we deduced energy transfer upconversion rate w 11 (s −1 ) originating from Er 3+ : 4 I 11/2 , 4 I 11/2 → 4 F 7/2 , 4 I 15/2 transitions.

In this work, we clearly demonstrate the efficacy of using XANES spectroscopy in conjunction with a Pilatus detector as a sensitive tool to allow the study of the oxidation process in GeTe alloys via depth profile analysis. On the basis of Ge K-edge XANES spectra, it was found that GeTe alloys do not oxidize readily after an initial native surface oxidation that occurs upon exposure to oxygen in the air at the elevated temperatures, 100 °C and 330 °C. We demonstrate that amorphous GeTe possesses a higher predisposition to oxidation than crystalline GeTe when exposed to the air at temperature of 100 °C. When the temperature is set to 330 °C in an air ambient, we show that the amorphous to crystal phase transition affects the oxidation process more significantly than the simple annealing of crystalline GeTe. We suggest that the higher tendency of GeTe films to oxidize during the phase transition is a consequence of the breaking of Ge–Ge bonds in the presence of oxygen atoms which subsequently leads to the extra formation of Ge–O bonds during crystallization.

2D van der Waals chalcogenides such as topological insulators and transition-metal dichalcogenides and their heterostructures are now at the forefront of semiconductor research. In this paper, we discuss the fundamental features and advantages of van der Waals bonded superlattices over conventional superlattices made of 3D materials and describe in more detail one practical example, namely, interfacial phase change memory based on GeTe–Sb 2 Te 3 superlattice structures.

In this paper, GeSe 2 thin film and glass ingot were prepared in a layered structure. Subsequently, the 2D amorphous monolayers were achieved from layered thin film and layered glass ingot. The thicknesses of monolayers from thin film range from 1.5 nm to 5 nm. And the thickness of monolayer from glass ingot is 7 μm. The fast cooling of material results in the formation of self-assembled monolayers. In the case of thin film, layers are connected with “bridge”. After doping of Ag, the precipitation of nano particles exfoliates the adjacent monolayers which can be further dispersed by etching of Ag particles. In the case of glass ingot, the composition changes at 1 % between adjacent monolayers, according to EDX (energy-dispersive X-ray spectroscopy) spectra. And the glass 2D monolayer can be mechanically peeled off from the glass ingot.

The properties of the materials are intimately related to the nature of the chemical bond. Research to explain the peculiarities of superionic materials by focusing on the bonding character of the materials is presented. In particular, a brief review of some fundamental aspects of superionic conductors is given based on the talk presented at “Solid State Chemistry 2018, Pardubice” in addition to some new results related to the subject. Specifically, the topics on bond fluctuation model of ionic conductors, the role of medium range structure in the ionic conductivity, bonding aspects of non-Arrhenius ionic conductivity and elastic properties of ionic conductors are discussed. Key concepts that are gained from these studies is stressed, such as the importance of the coexistence of different types of bonding, and the role of medium range structure in glasses for efficient ionic transport in solids. These concepts could help the development of new materials.

Quasi -ternary (AgI) x (HgS) 0.5− x /2 (GeS 2 ) 0.5− x /2 glasses, 10 −4 ≤ x ≤0.6 were studied over a wide composition range covering nearly 4 orders of magnitude in the mobile cation content. The glasses show a remarkable increase of the ionic conductivity by 12 orders of magnitude and exhibit two drastically different ion transport regimes: (i) a power-law critical percolation at x ≲0.04, and (ii) a modifier-controlled conductivity, exponentially dependent on x ≳0.1. Using Raman spectroscopy and high-energy X-ray diffraction supported by DFT modelling of the Raman spectra we show that the glass network is essentially formed by corner-sharing CS-GeS 4/2 tetrahedra. Mercury sulfide in glasses is dimorphic. The majority of Hg species (70% at x <0.2) exist as two-fold coordinated (HgS 2/2 ) n chains. Silver species have mixed (2I+2S) tetrahedral environment forming either edge–sharing ES-Ag 2 I 2 S 4/2 dimers or corner-sharing (CS-AgI 2/2 S 2/2 ) n chains. The relationship between the ionic transport and atomic structure of the glasses is discussed.

Silver photodiffusion is one of the attractive photo-induced changes observed in amorphous chalcogenides. In this research, we focus on amorphous S-rich germanium sulphide and study the kinetics of the silver photodiffusion by neutron reflectivity, as well as optical reflectivity. It was found from the neutron reflectivity profiles with 30 s time resolution that silver dissolved into the germanium sulphide layer, forming a metastable reaction layer between the Ag and the germanium sulphide layers, within 2 min of light exposure. Subsequently, silver slowly diffused from the metastable reaction layer to the germanium sulphide host layer until the Ag concentration in both layers became identical, effectively forming one uniform layer; this took approximately 20 min. Optical reflectivity reveals the electronic band structure of the sample, complementary to neutron reflectivity. It was found from the optical reflectivity measurement that the metastable reaction layer was a metallic product. The product could be Ag 8 GeS 6 -like form, which is regarded as the combination of GeS 2 and Ag 2 S, and whose backbone is composed of the GeS 4 tetrahedral units and the S atoms. We attribute the first quick diffusion to the capture of Ag ions by the latter S atoms, which is realised by the S–S bond in amorphous S-rich germanium sulphide, while we attribute the second slow diffusion to the formation of the Ag–Ge–S network, in which Ag ions are captured by the former GeS 4 tetrahedral units.

In order to investigate the full potential of the Electrical Impedance Spectroscopy (EIS) when used to address various aspects of conductive and dielectric response within the field of Condensed Matter Physics and Electrochemistry, a new analysis of the electrical impedance experiments has been undertaken. Within the framework of quantum mechanical band structure and using the concept of electrochemical potential for each of the relevant energies, the problem of electrical response in condensed phase has been formulated, using augmented Maxwell equations of Classical Electrodynamics, as a boundary value problem of a set of coupled, non-linear parabolic equations in energy, space and time. The result of this numerical analysis is a principal possibility of a complete electrical characterisation of both monocrystals, glassy solids and liquids. The EIS has been put in this way on a new qualitative level and should be considered now as the most general electrical experimental characterisation tool available. In this article, a methodology of numerical simulations of electrical response in condensed matter systems at classical frequencies (from ~1 THz down to dc) is presented and the numerical simulation results are then discussed, using monocrystalline Silicon, chalcogenide glass ion conductor Ag x (AsS 2 ) 1−x and simple aqueous chloride solution as experimental test cases. Some other unique results of the new EIS analysis will also be discussed. These include the possibility of a clear distinction between the contribution to the electrical response from bound and mobile electrical charges, the possibility of simultaneous and independent determination of the mobile electrical charges mobility and their density in one EIS experiment and incorporation of the interfacial regions of the system under test (SUT) as an essential part of the overall electrical response.

In the invited article, we review observations on changes in meteorite texture relevant to the early stages of formation of the Solar System based on the experimental shock wave loading of the material at the laboratory. Investigation of the physical and structural properties of high-pressure impacts on meteorites is important for few reasons, such as: Protection of the Earth from the near-Earth objects (NEOs); Study of processes that cannot yet be achieved under laboratory conditions; Understanding of conditions for asteroid mining.

In 2003–2014, a study on the effect of isotopic composition on the triple point temperature of neon was conducted under the framework of a Project involving laboratories from 11 countries. Natural neon from commercial sources of different isotopic composition, high-purity 20 Ne and 22 Ne isotopes, and certified artificial isotopic mixtures were used. The thermometric studies comprised: a) a total of 131 analytical assays from 3 laboratories on the isotopic composition of samples taken from 31 different bottles of neon with chemical gas purity 99.99 mol % to 99.9995+ mol %, including chemical impurities for some samples, with up to 12 assays per sample; b) multi-laboratory thermal analyses, with accuracies ranging up to better than 50 μK ( k ≈2), on 39 samples, almost all permanently sealed in metal cells, for the determination of the liquidus-point temperature of the triple point as a function of isotopic composition. The thermometric studies also constitute an international inter-comparison of thermal and analytical assays on the isotopic composition—and occasionally of the chemical impurities—of neon. These tests are critically needed for top-accuracy thermometry. The main results of the inter-comparison of the various chemical assays, and of the comparisons between the assays and the results of thermal analyses, are reported. They show discrepancies in x ( 20,21,22 Ne), especially for x ( 22 Ne), in ‘natural’ neon, for the same gas bottle, equivalent to an uncertainty of up to 165 μK ( k  = 1) in the triple point temperature, as measured by all testing laboratories, and of about 100 μK ( k  = 1) as measured from a single testing laboratory. This is an unsatisfactory situation for thermometry, since it is difficult to obtain a reliable and accurate isotopic assay for neon, thus limiting the accuracy of the realisation of the neon triple point temperature as a ITS-90 reference point to well above 50 μK. However, it also discloses a strong limitation in the relevant analytical chemistry.

Arrhenius parameters capturing the temperature dependence of radical polymerization propagation rate coefficients, k p , for methyl acrylate, butyl acrylate, and vinyl acetate in bulk are reported, based on the fitting of benchmark data sets compiled from independent laboratories using the pulsed-laser polymerization/size exclusion chromatography method. The reported k p values for acrylates hold for secondary-radical propagation and are needed to calculate effective propagation rate coefficients in situations where there is a significant population of mid-chain acrylate radicals resulting from backbiting, as will be the case at technically relevant temperatures. The results are compared to those previously reported for styrene and methacrylates to highlight the large differences in k p values seen between the major monomer families.

This recommendation proposes a definition for the term “chalcogen bond”; it is recommended the term is used to designate the specific subset of inter- and intramolecular interactions formed by chalcogen atoms wherein the Group 16 element is the electrophilic site.