Solids

20 pages, 2054 KiB

Open AccessReview

Solid-State Materials for Opto-Spintronics: Focus on Ferromagnets and 2D Materials

by Ana-Maria Florea (Raduta), Stefan Caramizoiu, Ana-Maria Iordache, Stefan-Marian Iordache and Bogdan Bita

Solids 2025, 6(2), 25; https://doi.org/10.3390/solids6020025 - 20 May 2025

Abstract

Opto-spintronics is an emerging field that focuses on harnessing light to manipulate and analyze electron spins to develop next-generation electronic devices. This paper explores recent progress and the role of solid-state materials in opto-spintronics by focusing on key classes of materials, such as [...] Read more.

Opto-spintronics is an emerging field that focuses on harnessing light to manipulate and analyze electron spins to develop next-generation electronic devices. This paper explores recent progress and the role of solid-state materials in opto-spintronics by focusing on key classes of materials, such as ferromagnetic semiconductors, two-dimensional (2D) transition metal dichalcogenides (TMDCs), and topological insulators. It examines the unique properties of ferromagnetic and antiferromagnetic materials and their ability to interact with light to affect spin dynamics, offering potential for improved sensing and quantum computing. By combining opto-spintronics with solid-state systems, spintronic devices could become faster and more efficient, leading to new technological advancements and scalable technologies. Full article

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13 pages, 1932 KiB

Open AccessReview

Diamond-Based Solvated Electron Generators: A Perspective on Applications in NRR, CO₂RR, and Pollutant Degradation

by Mattia Cattelan

Solids 2025, 6(2), 24; https://doi.org/10.3390/solids6020024 - 17 May 2025

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Abstract

The generation of solvated electrons (SEs) from solid-state sources represents a transformative approach to driving challenging reduction reactions under ambient conditions. Diamond, with its almost unique negative electron affinity (NEA) and tunable electronic properties, is emerging as a promising candidate for SE generation [...] Read more.

The generation of solvated electrons (SEs) from solid-state sources represents a transformative approach to driving challenging reduction reactions under ambient conditions. Diamond, with its almost unique negative electron affinity (NEA) and tunable electronic properties, is emerging as a promising candidate for SE generation in aqueous media. This perspective article reviews the current state of diamond-based SE generators and discusses their potential to catalyze sustainable nitrogen reduction (NRR) to ammonia, carbon dioxide reduction (CO₂RR), and the degradation of persistent environmental pollutants. Emphasis is placed on the fundamental processes enabling SE photoinjection from diamond to water, recent experimental breakthroughs, and the prospects for scalable, green applications. Full article

(This article belongs to the Special Issue Young Talents in Solid-State Sciences)

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22 pages, 4250 KiB

Open AccessArticle

Synthesis and Photocatalytic Properties of Manganese-Substituted Layered Perovskite-like Titanates A′₂La₂Mn_xTi_3−xO₁₀ (A′ = Na, H)

by Sergei A. Kurnosenko, Anastasiya I. Ustinova, Iana A. Minich, Vladimir V. Voytovich, Oleg I. Silyukov, Dmitrii V. Pankin, Olga V. Volina, Alina V. Kulagina and Irina A. Zvereva

Solids 2025, 6(2), 23; https://doi.org/10.3390/solids6020023 - 12 May 2025

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Abstract

The search for effective and reliable methods of photosensitization of oxide-based semiconductor materials is of great significance for their use in photocatalytic reactions of hydrogen production and environmental remediation under natural sunlight. The present study is focused on partial substitution of titanium with [...] Read more.

The search for effective and reliable methods of photosensitization of oxide-based semiconductor materials is of great significance for their use in photocatalytic reactions of hydrogen production and environmental remediation under natural sunlight. The present study is focused on partial substitution of titanium with manganese in the structure of layered perovskite-like titanate Na₂La₂Ti₃O₁₀, which was employed to yield a series of photocatalytically active materials, Na₂La₂Mn_xTi_3−xO₁₀ (x = 0.002–1.0), as well as their protonated forms H₂La₂Mn_xTi_3−xO₁₀ and nanosheets. It was established that the manganese cations Mn⁴⁺ are embedded in the middle sublayer of oxygen octahedra in the perovskite slabs La₂Mn_xTi_3−xO₁₀²⁻ and that the maximum achievable manganese content x in the products is ≈0.9. The partial cationic substitution in the perovskite sublattice led to a pronounced contraction of the optical band gap from 3.20 to 1.35 eV (depending on x) and, therefore, allowed the corresponding photocatalysts to utilize not only ultraviolet, but also visible and near-infrared light with wavelengths up to ≈920 nm. The materials obtained were tested as photocatalysts of hydrogen evolution from aqueous methanol, and the greatest activity in this reaction was demonstrated by the samples with low manganese contents (x = 0.002–0.01). However, the materials with greater substitution degrees may be of high interest for use in other photocatalytic processes and, especially, in thermophotocatalysis due to their improved ability to absorb the near-infrared part of solar radiation. Full article

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14 pages, 3551 KiB

Open AccessArticle

Influence of Germanium Sulfide on the Structure, Ag-Ion Conductivity and Stability of Glasses in the GeS₂-Sb₂S₃-AgI System

by Viktor Markov, Talib Farziev and Nikita Dybin

Solids 2025, 6(2), 22; https://doi.org/10.3390/solids6020022 - 9 May 2025

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Abstract

This article discusses the superionic glassy GeS₂-Sb₂S₃-AgI system with mobile silver ions as a material for creating new energy-efficient solid-state ion emitters. The effect of replacing silver iodide with germanium sulfide on the structure of the electrolyte, [...] Read more.

This article discusses the superionic glassy GeS₂-Sb₂S₃-AgI system with mobile silver ions as a material for creating new energy-efficient solid-state ion emitters. The effect of replacing silver iodide with germanium sulfide on the structure of the electrolyte, activation energy of diffusion, and specific ionic conductivity was studied. Electrolytes (2.5 + x)GeS₂-27.5Sb₂S₃-(70 − x)AgI, x = 0, 5, 10, 15 were synthesized using the melt-quenching technique in evacuated quartz ampoules. The temperature dependence of conductivity and glass stability parameters (Hruby’s, Weinberg’s and Lu–Liu’s) were determined for them, and the mechanism for increasing glass-forming ability was clarified. It was shown that the presence of iodine in a germanium structural unit is more preferable than in an antimony structural unit; germanium structural units compete for iodine, reducing the number of SbI₃ crystallization centers and chain terminations, resulting in additional structural connectivity and stability. It was shown that when silver iodide was replaced by germanium sulfide, the decrease in conductivity due to the reduction in charge carriers was less than expected due to the expansion of the conduction channels. Full article

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11 pages, 4492 KiB

Open AccessArticle

Fabrication of High-Quality Er³⁺-Yb³⁺ Co-Doped Phosphate Glasses with Low Residual Hydroxyl Group Content

by Yonglong Liu, Siyu Zhu, Jianan Huang, Xinyu Ye, Chunxiao Liu and Liaolin Zhang

Solids 2025, 6(2), 21; https://doi.org/10.3390/solids6020021 - 8 May 2025

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Abstract

Rare earth-doped phosphate glasses have found widespread application in the field of solid-state and fiber laser technologies. Nevertheless, the fabrication of high-quality rare earth-doped phosphate glasses with minimal residual hydroxyl groups remains a significant challenge. To address this, a two-step melting process was [...] Read more.

Rare earth-doped phosphate glasses have found widespread application in the field of solid-state and fiber laser technologies. Nevertheless, the fabrication of high-quality rare earth-doped phosphate glasses with minimal residual hydroxyl groups remains a significant challenge. To address this, a two-step melting process was utilized in this work to synthesize Er³⁺-Yb³⁺ co-doped phosphate glasses with low residual hydroxyl group content and improved optical quality. When re-melted under a N₂ atmosphere at 900 °C for 12 to 16 h, the hydroxyl absorption coefficient (α_-OH) decreased to ~1 cm⁻¹. The structural and compositional characteristics of the glass remained essentially unchanged throughout the re-melting process. The weak broadband absorption in the visible range and the red-shift of the ultraviolet absorption edge were attributed to the reduction in residual hydroxyl group content rather than carbon contamination. The dehydroxylation mechanism was governed by the physical diffusion of hydroxyl groups within the glass matrix. Full article

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11 pages, 1904 KiB

Open AccessFeature PaperArticle

Research on the Particle Growth Process of Colloidal Silica Derived from the Sol-Gel Process Using Active Silicic Acid Solutions

by Kazuaki Higuchi, Yujia Liu and Masafumi Unno

Solids 2025, 6(2), 20; https://doi.org/10.3390/solids6020020 - 6 May 2025

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Abstract

The influence of the quantity of silanol in an active silicic acid solution (ASAS) on the growth rate of colloidal silica particles was investigated. The quantity of silanol in the ASAS was controlled by varying the acid concentration as a hydrolysis catalyst for [...] Read more.

The influence of the quantity of silanol in an active silicic acid solution (ASAS) on the growth rate of colloidal silica particles was investigated. The quantity of silanol in the ASAS was controlled by varying the acid concentration as a hydrolysis catalyst for tetramethoxysilane (TMOS). As expected, the particle growth rate was confirmed to be a function of the acid concentration in the water used to prepare the ASAS. In addition, when the entire process was conducted under basic conditions to obtain spherical particles, the initial basicity had a secondary influence on the particle growth rate. When a partial process was conducted under acidic conditions to obtain morphologically modified particles, the low acidity was found to have a secondary influence on the particle growth rate. Furthermore, it was clarified that the relative silica deposition rate based on acid-free ASAS could be predicted by assuming the seed particle size at the time it was determined. Thus, a production control system was established for highly purified colloidal silica using ASAS derived from TMOS. Full article

(This article belongs to the Special Issue Hybrid Sol-Gel Materials)

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19 pages, 8735 KiB

Open AccessArticle

Binder Influence on Polyantimonic Acid-Based Membranes’ Electrical Behavior for Low-Temperature Fuel Cells

by Sofia Mendes and Pedro Faia

Solids 2025, 6(2), 19; https://doi.org/10.3390/solids6020019 - 17 Apr 2025

Viewed by 334

Abstract

The development of innovative proton-conducting materials for low-temperature fuel cells (FCs) is, today, a central topic among the scientific community. Polyantimonic acid (PAA) is characterized by high conductivity and sufficient thermal stability; however, PAA-based solid membrane fabrication with high proton conductivity remains challenging. [...] Read more.

The development of innovative proton-conducting materials for low-temperature fuel cells (FCs) is, today, a central topic among the scientific community. Polyantimonic acid (PAA) is characterized by high conductivity and sufficient thermal stability; however, PAA-based solid membrane fabrication with high proton conductivity remains challenging. Additionally, PAA cannot be compacted into solid shaped electrolytes without a binder. In a previous work, using a fluoroplastic binder, the authors fabricated and investigated proton conductivity of bulk PAA-based membranes in the temperature range 25–250 °C. In the present research, the authors opted to use another binder, poly(vinyl alcohol), PVA (which already allowed to obtain PAA sensors with higher sensitivity to moisture, low hysteresis, and similar aging than the produced previously with the fluoroplastic binder), for fabricating new solid membranes. The sample’s structure and morphology were studied using diverse experimental techniques (Thermogravimetric analysis, X-ray diffraction analysis, etc.). Electrical Impedance spectroscopy, EIS, was used to assess the electrical response and respective time stability of the membranes; it also allowed the development of an equivalent model circuit to better interpret the samples’ electrical behavior and respective contributions. The samples with 20 wt% PVA content showed improved protonic conductivity and chemical stability up to 100 °C, when compared to previous prepared and reported ones using the fluoroplastic binder. Full article

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23 pages, 4225 KiB

Open AccessArticle

Modification of the Adsorption Capacity of Brick Industry Fly Ash for the Removal of Cd(II)

by León Fernando Pérez-Chauca, Luz Genara Castañeda-Pérez, Luis Américo Carrasco-Venegas, Juan Luis Quispe-Cisneros, Alfredo Torres-Garay and José Vulfrano González-Fernández

Solids 2025, 6(2), 18; https://doi.org/10.3390/solids6020018 - 16 Apr 2025

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Abstract

Fly ash, a byproduct of coal burning and gasification, is a significant source of global pollution and is classified as hazardous waste. However, physicochemical treatments can improve their adsorption capacity by increasing their surface area. This research aimed to enhance the adsorption capacity [...] Read more.

Fly ash, a byproduct of coal burning and gasification, is a significant source of global pollution and is classified as hazardous waste. However, physicochemical treatments can improve their adsorption capacity by increasing their surface area. This research aimed to enhance the adsorption capacity of fly ash from the brick manufacturing industry to remove Cd(II) ions by optimizing its surface area. The treatment process was designed with two factors: sodium hydroxide concentration and stirring time, each evaluated at three levels. The modification was confirmed through X-ray diffraction analysis of its mineralogical composition. Using the BET method, the initial fly ash exhibited a surface area of 8.59 m²/g, which increased to a maximum of 33.99 m²/g after treatment. The proposed modification method successfully quadrupled the surface area under optimal conditions: 2.0 M NaOH concentration and 60 min of stirring. The 3² factorial design shows that the highest degree of Cd(II) removal is 99.75%, which is achieved using the modified fly ash with a surface area of 33.99 m²/g under favorable operating conditions of 30 min and 600 rpm stirring speed. Full article

(This article belongs to the Special Issue Young Talents in Solid-State Sciences)

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18 pages, 7346 KiB

Open AccessArticle

Optimizing the Mechanical Properties and Corrosion Performance of Low-Alloyed Mg-Zn-Ca Alloy by Regulating Zn/Ca Atomic Ratios

by Yuan Jin, Shaoyuan Lyu, Qianqian Yu and Minfang Chen

Solids 2025, 6(2), 17; https://doi.org/10.3390/solids6020017 - 14 Apr 2025

Viewed by 387

Abstract

The microstructural, mechanical and corrosion properties of low-alloyed Mg-Zn-Ca alloys with different Zn/Ca atomic ratios were investigated. The results show that the microstructure of the extruded Mg-1Zn-0.3Ca (ZX1.0) alloy mainly consists of α-Mg and Ca₂Mg₆Zn₃ phases and a [...] Read more.

The microstructural, mechanical and corrosion properties of low-alloyed Mg-Zn-Ca alloys with different Zn/Ca atomic ratios were investigated. The results show that the microstructure of the extruded Mg-1Zn-0.3Ca (ZX1.0) alloy mainly consists of α-Mg and Ca₂Mg₆Zn₃ phases and a small amount of Mg₂Ca phase. In contrast, the Mg₂Ca phase disappears in the alloys Mg-1.4Zn-0.3Ca (ZX1.4), Mg-1.8Zn-0.3Ca (ZX1.8) and Mg-2.3Zn-0.5Ca (ZX2.3). The Ca₂Mg₆Zn₃ phases are mainly distributed along the extrusion direction, showing irregular particle shapes and banded particles. Meanwhile, the grain size of the extruded Mg-Zn-Ca alloy is reduced gradually with the increase of the Zn and Ca contents, decreasing from 1.87 μm in ZX1.0 to 1.28 μm in ZX2.3 alloy. Fine grain strengthening and second-phase strengthening increase the yield strength and ultimate tensile strength of the alloy. In addition, when the Zn/Ca ratio is the same, the total elemental content dominates the effect on alloy properties. When increasing the Zn/Ca ratio, the potential difference between Ca₂Mg₆Zn₃ and the Mg matrix increased, resulting in an increase in galvanic corrosion. The negative effect of the volume fraction of the second phase and the positive effect of the fine grain size determine the corrosion performance together. Therefore, ZX1.8 exhibits the best corrosion resistance, of 0.14 mm/y. Full article

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26 pages, 3432 KiB

Open AccessArticle

Pristine and Reassembled Nanosheets of Layered Perovskite-like Titanates HLnTiO₄ and H₂Ln₂Ti₃O₁₀ (Ln = La, Nd) as Photocatalysts for Hydrogen Evolution

by Sergei A. Kurnosenko, Oleg I. Silyukov, Ivan A. Rodionov, Iana A. Minich and Irina A. Zvereva

Solids 2025, 6(2), 16; https://doi.org/10.3390/solids6020016 - 2 Apr 2025

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Abstract

Layered Ruddlesden–Popper titanates HLnTiO₄ and H₂Ln₂Ti₃O₁₀ (Ln = La, Nd) have been exfoliated into nanosheets in aqueous tetrabutylammonium hydroxide and systematically investigated as hydrogen evolution photocatalysts. The nanosheets were tested both in as-prepared pristine form [...] Read more.

Layered Ruddlesden–Popper titanates HLnTiO₄ and H₂Ln₂Ti₃O₁₀ (Ln = La, Nd) have been exfoliated into nanosheets in aqueous tetrabutylammonium hydroxide and systematically investigated as hydrogen evolution photocatalysts. The nanosheets were tested both in as-prepared pristine form and after reassembly by two methods (simple filtration and precipitation by hydrochloric acid). The nanosheet-based samples demonstrated by up to 88 times greater photocatalytic performance in comparison with the bulk precursors and, after modification with a Pt cocatalyst, provided apparent quantum efficiency of hydrogen generation up to 14.2% in 1 mol.% aqueous methanol and 3.15% in pure water. It was established that the form in which the nanosheets are used strongly affects the hydrogen production efficiency: the latter typically decreases when moving from the pristine nanosheets to filtered ones and then to those restacked by hydrochloric acid, which is determined by the difference in their physical–chemical characteristics being influenced by the reassembly approach. Full article

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18 pages, 18008 KiB

Open AccessFeature PaperArticle

Insights into the Electrochemical Synthesis and Supercapacitive Behaviour of 3D Copper Oxide-Based Nanostructures

by Gintautas Jonkus, Ramunas Levinas, Natalia Tsyntsaru and Henrikas Cesiulis

Solids 2025, 6(2), 15; https://doi.org/10.3390/solids6020015 - 1 Apr 2025

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Abstract

In this study, nanostructured copper oxide-based films with crystallite size below 10 nm were electrochemically synthesized on copper foil and foam electrodes and investigated for their supercapacitive behaviour. The synthesis was carried out via cyclic voltammetry (CV) for up to 1000 cycles in [...] Read more.

In this study, nanostructured copper oxide-based films with crystallite size below 10 nm were electrochemically synthesized on copper foil and foam electrodes and investigated for their supercapacitive behaviour. The synthesis was carried out via cyclic voltammetry (CV) for up to 1000 cycles in an alkaline electrolyte. By tuning the upper vertex potential (−0.3 V to 0.65 V vs. Ag/AgCl), both phase composition (Cu₂O, Cu(OH)₂, CuO) and morphology (grains, nanoneedles, nanoplatelets) were precisely controlled, demonstrating the versatility of this approach. The kinetics of oxide/hydroxide film formation on foil and foam electrodes were analysed based on EIS data that were interpreted in the frame of equivalent electric circuits and their changes with potential. The capacitive properties of the synthesized films were evaluated using CV in the potential range of 0 V–0.65 V, and the optimized CuO film synthesized on Cu foam exhibited a high specific capacitance of 1380 mF cm⁻². An energy density of 0.061 mWh cm⁻² and power density of 1.28 mW cm⁻² were obtained at 10 mA cm⁻² discharge current. Charge–discharge cycling at 100 mV s⁻¹ for 1000 cycles indicated an initial capacitance increase followed by stable retention, highlighting the structural integrity and electrochemical stability of the films obtained on 3D foam. These findings provide valuable insights into the controlled electrochemical synthesis of copper oxide nanostructures and their potential for high-performance capacitor applications. Full article

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Solids, Volume 6, Issue 2 (June 2025) – 11 articles

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