Solids, Volume 4, Issue 3 (September 2023) – 8 articles

A generic expression is derived for the dynamical response function of metal films, with conductivity tensors as the only input. The semi-classical model is then used to provide an analytical expression for the conductivity tensor, thus establishing a kinetic theory for the response function. A major advantage of the theory is its ability to handle surface roughness effects through the use of the so-called specularity parameter. We applied the theory to study the properties of surface plasma waves. It is found that surface roughness does not affect the dispersion, but rather the decay rate of these waves. Furthermore, it significantly affects the spectral weight carried by the SPW resonances, which diminishes toward zero as the specularity parameter approaches unity. Full article

Polystyrene has limited adhesivity to inorganic materials such as metals. However, the inorganic surface can be treated to enhance bonding to energetically stable polystyrene. This concept is verified in this paper with organosilane aminopropyltriethoxysilane (APTES) as the coupling agent primed on hydroxylated aluminum alloy AA2024-T3. We characterize the structural integrity and electrical impedance of the polystyrene coating on APTES-primed surfaces with different cured conditions after exposure to 3.5 wt.% NaCl solution for seven days. The results show that top-coated polystyrene on APTES is more structurally intact and less electrically conductive than the polystyrene coating alone. The coating layer made of top-coating polystyrene on a curing APTES film has the largest water uptake rate in the early stage of immersion in the corrosion solution. In the later stage, all coating layers tested regained their impedance while losing structural integrity. The charge transfer in the double layer of coated specimens for all types of coatings tested is predominantly through capacitance-based charging/discharging, presumably governed by the adsorption mechanism of ions at the coating/substrate interface. Full article

This article reports the pressure-dependent crystal radii of Mg, Si, Ge, Be, Fe, Ca, Sr, Ba, Al, Ti, Li, Na, K, Cs, and of some rare earths, that is: the major Earth mantle elements, important minor, and some trace elements. Pressure dependencies of O²⁻, Cl⁻, and Br⁻ are also reported. It is shown that all examined cation radii vary linearly with pressure. Cation radii obey strict correlations between ionic compressibilities and reference 0 GPa radii, thus reducing previous empirical rules of the influence of valence, ion size, and coordination to a simple formula. Both cation and anion radii are functions of nuclear charge number and a screening function which for anions varies with pressure, and for cations is pressure-independent. The pressure derivative of cation radii and of the anion radii at high pressure depends on electronegativity with power −1.76. Full article

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF₄/H₂ etching gas mixture with a constant volumetric flow of 30 sccm and a variable H₂ concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ c_HF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements. Full article

The metal–insulator transition induced by the gate electric field in the charge order phase of the $\alpha$-(BEDT-TTF)${}_2$I${}_3$ single-crystal field-effect transistor (FET) structure was clearly observed near the phase transition temperature. An abrupt increase in the electrical conductance induced by the applied gate electric field was evident, which corresponds to the partial dissolution of the charge order phase triggered by the gate electric field. The estimated nominal dissolved charge order region (i.e., the gate-induced metallic region) was overestimated in 130–150 K, suggesting additional effects such as Joule heating. On the other hand, in the lower temperature region below 120 K, the corresponding dissolved charge order was several monolayers of BEDT-TTF, suggesting that it is possible to dissolve the charge order phase within the bistable temperature region. Full article

Iron-containing nickel sulfides, selenides, and sulfoselenides were synthesized via a simple two-step hydrothermal reaction (temperature ≤ 160 °C) for their application as electrocatalysts in the oxygen evolution reaction (OER) in an alkaline solution (1 mol L⁻¹ KOH). The study demonstrated that iron-containing nickel cobalt sulfides and selenides exhibit superior OER performance with lower overpotentials compared to iron-free nickel cobalt sulfide and selenide, which highlights the significant role of iron in enhancing OER nickel cobalt electrocatalysts: Fe_0.1Ni_1.4Co_2.9(S_0.87O_0.13)₄, η₅₀ = 318 mV; Fe_0.2Ni_1.5Co_2.8(S_0.9O_0.1)₄, η₅₀ = 310 mV; Fe_0.3Ni_1.2Co_2.5(S_0.9O_0.1)₄, η₅₀ = 294 mV; Fe_0.6Ni_1.2Co_2.5(S_0.83O_0.17)₄, η₅₀ = 294 mV; Fe_0.4Ni_0.7Co_1.6(Se_0.81O_0.19)₄, η₅₀ = 306 mV compared to Ni_1.0Co_2.1(S_0.9O_0.1)₄, η₅₀ = 346 mV; and Ni_0.7Co_1.4(Se_0.85O_0.15)₄, η₅₀ = 355 mV (all values at current densities η₅₀ of 50 mA cm⁻²). Furthermore, the iron-containing nickel cobalt sulfoselenide Fe_0.5Ni_1.0Co_2.0(S_0.57Se_0.25O_0.18)₄ displayed exceptional OER performance with η₅₀ = 277 mV, surpassing the benchmark RuO₂ electrode with η₅₀ = 299 mV. The superior performance of the sulfoselenide was attributed to its low charge transfer resistance (Rct) of 0.8 Ω at 1.5 V vs. the reversible hydrogen electrode (RHE). Moreover, the sulfoselenide demonstrated remarkable stability, with only a minimal increase in overpotential (η₅₀) from 277 mV to 279 mV after a 20 h chronopotentiometry test. These findings suggest that trimetallic iron, nickel and cobalt sulfide, selenide, and especially sulfoselenide materials hold promise as high-performance, cost-effective, and durable electrocatalysts for sustainable OER reactions. This study provides a valuable approach for the development of efficient electrocatalytic materials, contributing to the advancement of renewable energy technologies. Full article

Several ternary rare-earth metals containing titanium aluminum intermetallics in the RE₂TiAl₃ series (RE = Y, Gd–Lu) have been synthesized from the elements using arc-melting techniques. All compounds crystallize in the trigonal crystal system with rhombohedral space group R3m (Z = 3) and lattice parameters ranging between a = 582–570 and c = 1353–1358 pm. They adopt the Mg₂Ni₃Si-type structure, which is an ordered superstructure of the cubic Laves phase MgCu₂ and has been observed for Al intermetallics for the first time. Tetrahedral [TiAl₃] entities that are connected over all corners form a network where the empty [TiAl₃] tetrahedra exhibit a full Ti/Al ordering based on the single crystal results. The Al atoms are arranged into 6³ Kagomé nets, while the Ti atoms connect these nets over the triangular units. In the cavities of this three-dimensional arrangement, the RE cations can be found forming a distorted diamond-type substructure. Magnetic measurements revealed that Y₂TiAl₃ and Lu₂TiAl₃ are Pauli paramagnetic substances, in line with the metallic character. The other compounds exhibit paramagnetism with antiferromagnetic ordering at a maximum Néel temperature of T_N = 26.1(1) K for Gd₂TiAl₃. Full article

This study investigated the allowability of materials in the laser powder melting process, with a focus on powder mixing as a means of adjusting the material composition quickly and cost-effectively. By mixing different powders, a desired alloy can be created during additive processing without the need to produce new powder, which can be expensive. However, one of the main challenges in this process is the segregation of powders, which can lead to non-homogeneous alloys. To address this challenge, the study examined the use of a single component 316L mixed with 1% and 5% copper powder in the additive processing. The results showed that homogeneous components with a uniform and targeted copper content could be produced. However, the mechanical-technological properties of both alloys were lower than those of 316L in situ. To optimize and extend this study, further investigation could be conducted to improve the homogeneity of the powder mixture and to enhance the mechanical-technological properties of the alloys produced. This could involve exploring different alloy designs, optimizing the laser powder melting process parameters, and using advanced characterization techniques to gain a deeper understanding of the microstructure and properties of the alloys. By addressing these challenges, the laser powder melting process could become an even more promising method for producing customized alloys with tailored properties. Full article