Low-Temperature Rapid Sintering of Dense Cubic Phase ZrW2−xMoxO8 Ceramics by Spark Plasma Sintering and Evaluation of Its Thermal Properties

In this study, we report a low-temperature approach involving a combination of a sol–gel hydrothermal method and spark plasma sintering (SPS) for the fabrication of cubic phase ZrW_2−xMo_xO₈ (0.00 ≤ x ≤ 2.00) bulk ceramics. The cubic-ZrW_2−xMo_xO₈ (0.00 ≤ x ≤ 1.50) bulk ceramics were successfully synthesized within a temperature range of 623–923 K in a very short amount of time (6–7 min), which is several hundred degrees lower than the typical solid-state approach. Meanwhile, scanning electron microscopy and density measurements revealed that the cubic-ZrW_2−xMo_xO₈ (0.00 ≤ x ≤ 1.50) bulk ceramics were densified to more than 90%. X-ray diffraction (XRD) results revealed that the cubic phase ZrW_2−xMo_xO₈ (0.00 ≤ x ≤ 1.5) bulk ceramics, as well as the sol–gel-hydrothermally synthesized ZrW_2−xMo_xO₇(OH)₂·2H₂O precursors correspond to their respective pure single phases. The bulk ceramics demonstrated negative thermal expansion characteristics, and the coefficients of negative thermal expansion were shown to be tunable in cubic-ZrW_2−xMo_xO₈ bulk ceramics with respect to x value and sintering temperature. The cubic-ZrW_2−xMo_xO₈ solid solution can thus have potential applications in electronic devices such as heat sinks that require regulation of thermal expansion.     

The Gd2−xMgxZr2O7−x/2 Solid Solution: Ionic Conductivity and Chemical Stability in the Melt of LiCl-Li2O

Materials with pyrochlore structure A₂B₂O₇ have attracted considerable attention owing to their various applications as catalysts, sensors, electrolytes, electrodes, and magnets due to the unique crystal structure and thermal stability. At the same time, the possibility of using such materials for electrochemical applications in salt melts has not been studied. This paper presents the new results of obtaining high-density Mg²⁺-doped ceramics based on Gd₂Zr₂O₇ with pyrochlore structure and comprehensive investigation of the electrical properties and chemical stability in a lithium chloride melt with additives of various concentrations of lithium oxide, performed for the first time. The solid solution of Gd_2−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.10) with the pyrochlore structure was obtained by mechanically milling stoichiometric mixtures of the corresponding oxides, followed by annealing at 1500 °C. The lattice parameter changed non-linearly as a result of different mechanisms of Mg²⁺ incorporation into the Gd₂Zr₂O₇ structure. At low dopant concentrations (x ≤ 0.03) some interstitial positions can be substituted by Mg²⁺, with further increasing Mg²⁺-content, the decrease in the lattice parameter occurred due to the substitution of host-ion sites with smaller dopant-ion. High-density ceramics 99% was prepared at T = 1500 °C. According to the results of the measurements of electrical conductivity as a function of oxygen partial pressure, all investigated samples were characterized by the dominant ionic type of conductivity over a wide range of pO₂ (1 × 10^–18 ≤ pO₂ ≤ 0.21 atm) and T < 800 °C. The sample with the composition of x = 0.03 had the highest oxygen-ion conductivity (10⁻³ S·cm⁻¹ at 600 °C). The investigation of chemical stability of ceramics in the melt of LiCl with 2.5 mas.% Li₂O showed that the sample did not react with the melt during the exposed time of one week at the temperature of 650 °C. This result makes it possible to use these materials as oxygen activity sensors in halide melts.     

Mg2+ Doping Effects on the Structural and Dielectric Properties of CaCu3Ti4O12 Ceramics Obtained by Mechanochemical Synthesis

In this study, ceramic CaCu₃Ti₄O₁₂ (CCTO) and CaCu_3−xMg_xTi₄O₁₂ solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The effects of the Mg²⁺ ion concentration and sintering time on the dielectric response in the prepared ceramics were investigated and discussed. It was demonstrated that, by the use of a sufficiently high energy of mechanochemical treatment, it is possible to produce a crystalline product after only 2 h of milling the mixture of the oxide substrates. Both the addition of magnesium ions and the longer sintering time of the mechanochemically-produced ceramics cause excessive grain growth and significantly affect the dielectric properties of the materials. The X-ray diffraction (XRD) analysis showed that all of the as-prepared solid solutions, CaCu_3−xMg_xTi₄O₁₂ (0.0 ≤ x ≤ 0.5), regardless of the sintering time, exhibit a cubic perovskite single phase. The dielectric study showed two major contributions associated with the grains and the grain boundaries. The analysis of the electric modules of these ceramics confirmed the occurrence of Maxwell–Wagner type relaxation, which is dependent on the temperature.     

Stoichiometry and Morphology Analysis of Thermally Deposited V2O5−x Thin Films for Si/V2O5−x Heterojunction Solar Cell Applications

In recent decades, dopant-free Si-based solar cells with a transition metal oxide layer have gained noticeable research interest as promising candidates for next-generation solar cells with both low manufacturing cost and high power conversion efficiency. Here, we report the effect of the substrate temperature for the deposition of vanadium oxide (V₂O_5−x, 0 ≤ X ≤ 5) thin films (TFs) for enhanced Si surface passivation. The effectiveness of SiO_x formation at the Si/V₂O_5−x interface for Si surface passivation was investigated by comparing the results of minority carrier lifetime measurements, X-ray photoelectron spectroscopy, and atomic force microscopy. We successfully demonstrated that the deposition temperature of V₂O_5−x has a decisive effect on the surface passivation performance. The results confirmed that the aspect ratio of the V₂O_5−x islands that are initially deposited is a crucial factor to facilitate the transport of oxygen atoms originating from the V₂O_5−x being deposited to the Si surface. In addition, the stoichiometry of V₂O_5−x TFs can be notably altered by substrate temperature during deposition. As a result, experimentation with the fabricated Si/V₂O_5−x heterojunction solar cells confirmed that the power conversion efficiency is the highest at a V₂O_5−x deposition temperature of 75 °C.     

Characterization of Ionic Transport in Li2O-(Mn:Fe)2O3-P2O5 Glasses for Li Batteries

We present a systematic study of the lithium-ion transport upon the mixed manganese-iron oxide phosphate glasses 3Li₂O-xMn₂O₃-(2-x)Fe₂O₃-3P₂O₅(LM_xF_2−xPO; 0≤ x ≤2.0) proposed for the use in a cathode for lithium secondary batteries. The glasses have been fabricated using a solid reaction process. The electrical characteristics of the glass samples have been characterized by electrical impedance in the frequency range from 100 Hz to 30 MHz and temperature from 30 °C to 240 °C. Differential thermal analysis and X-ray diffraction were used to determine the thermal and structural properties. It has been observed that the dc conductivity decreases, but the activation energies of dc and ac and the glass-forming ability increase with the increasing Mn₂O₃ content in LM_xF_2−xPO glasses. The process of the ionic conduction and the relaxation in LM_xF_2−xPO glasses are determined by using power–law, Cole–Cole, and modulus methods. The Li⁺ ions migrate via the conduction pathway of the non-bridging oxygen formed by the depolymerization of the mixed iron–manganese–phosphate network structure. The mixed iron–manganese content in the LM_xF_2−xPO glasses constructs the sites with different depths of the potential well, leading to low ionic conductivity.     

Tailoring the Stability of Ti-Doped Sr2Fe1.4TixMo0.6−xO6−δ Electrode Materials for Solid Oxide Fuel Cells

In this work, the stability of Sr₂(FeMo)O_6−δ-type perovskites was tailored by the substitution of Mo with Ti. Redox stable Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ (x = 0.1, 0.2 and 0.3) perovskites were successfully obtained and evaluated as potential electrode materials for SOFCs. The crystal structure as a function of temperature, microstructure, redox stability, and thermal expansion properties in reducing and oxidizing atmospheres, oxygen content change, and transport properties in air and reducing conditions, as well as chemical stability and compatibility towards typical electrolytes have been systematically studied. All Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ compounds exhibit a regular crystal structure with Pm-3m space group, showing excellent stability in oxidizing and reducing conditions. The increase of Ti-doping content in materials increases the thermal expansion coefficient (TEC), oxygen content change, and electrical conductivity in air, while it decreases the conductivity in reducing condition. All three materials are stable and compatible with studied electrolytes. Interestingly, redox stable Sr₂Fe_1.4Ti_0.1Mo_0.5O_6−δ, possessing 1 μm grain size, low TEC (15.3 × 10⁻⁶ K⁻¹), large oxygen content change of 0.72 mol·mol⁻¹ between 30 and 900 °C, satisfactory conductivity of 4.1–7.3 S·cm⁻¹ in 5% H₂ at 600–800 °C, and good transport coefficients D and k, could be considered as a potential anode material for SOFCs, and are thus of great interest for further studies.     

DC and AC Conductivity,Biosolubility and Thermal Properties of Mg-Doped Na2O–CaO–P2O5 Glasses

Bioactive glasses have recently been extensively used to replace, regenerate, and repair hard tissues in the human body because of their ability to bond with living tissue. In this work, the effects of replacing Na₂O with MgO on the electrical, biosolubility, and thermal properties of the target glass 10Na₂O–60P₂O₅–30CaO (in mol%) were investigated. The electrical properties of the glasses were studied with the impedance spectroscopy technique. At 473 K, DC conductivity values decreased from 4.21 × 10⁻¹¹ to 4.21 × 10⁻¹² S cm⁻¹ after complete substitution of MgO for Na₂O. All samples had a similar activation energy of the DC conduction process ~1.27 eV. Conduction mechanisms were found to be due to hop of ions: Na⁺, Mg²⁺_, and probable H⁺. FTIR analysis showed that, as the Mg content increased, the Q² unit (PO₂⁻) shifted towards higher wavenumbers. The proportion of Q³ unit (P₂O₅) decreased in the glass structure. This confirmed that the replacement of Na⁺ by Mg²⁺ was accompanied by concurrent polymerization of the calcium–phosphate glass network. The biosolubility test in the phosphate-buffered saline solution showed that the magnesium addition enhanced the biosolubility properties of Na₂O–CaO–P₂O₅ glasses by increasing their dissolution rate and supporting forming CaP-rich layers on the surface. The glass transition temperature increased, and thermal stability decreased substantially upon substitution of Na₂O by MgO.     

Peculiarities of the Phase Formation during Electroconsolidation of Al2O3–SiO2–ZrO2 Powders Mixtures

This paper is devoted to the sintering process of Al₂O₃–SiO₂–ZrO₂ ceramics. The studied method was electroconsolidation with directly applied electric current. This method provides substantial improvements to the mechanical properties of the sintered samples compared to the traditional sintering in the air. The research covered elemental and phase analysis of the samples, which revealed phase transition of high-alumina solid solutions into mullite and corundum. Zirconia was represented mainly by tetragonal phase, but monoclinic phase was present, too. Electroconsolidation enabled samples to reach a density of 3.0 g/cm³ at 1300 °C, while the sample prepared by traditional sintering method obtained it only at 1700 °C. For the composite Al₂O₃—20 wt.% SiO₂—10 wt.% ZrO₂ fabricated by electroconsolidation, it was demonstrated that fracture toughness was higher by 20–30%, and hardness was higher by 15–20% compared to that of samples sintered traditionally. Similarly, the samples fabricated by electroconsolidation exhibited elastic modulus E higher by 15–20%. The hypothesis was proposed that the difference in mechanical and physical properties could be attributed to the peculiarities of phase formation processes during electroconsolidation.     

HfAlOx/Al2O3 Bilayer Dielectrics for a Field Effect Transistor on a Hydrogen-Terminated Diamond

In this work, a hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with HfAlO_x/Al₂O₃ bilayer dielectrics is fabricated and characterized. The HfAlO_x/Al₂O₃ bilayer dielectrics are deposited by the atomic layer deposition (ALD) technique, which can protect the H-terminated diamond two-dimensional hole gas (2DHG) channel. The device demonstrates normally-on characteristics, whose threshold voltage (V_TH) is 8.3 V. The maximum drain source current density (I_DSmax), transconductance (G_m), capacitance (C_OX) and carrier density (ρ) are −6.3 mA/mm, 0.73 mS/mm, 0.22 μF/cm² and 1.53 × 10¹³ cm⁻², respectively.     

Electrochemical Degradation of Tetracycline Using a Ti/Ta2O5-IrO2 Anode: Performance,Kinetics, and Degradation Mechanism

Tetracycline (TC) is widely used in production and in life. The high volume of its use and the difficulty of its disposal have become the most important causes of environmental pollution. A suitable method needs to be found to solve this problem. In this study, the Ti/Ta₂O₅-IrO₂ electrode was characterized for its surface morphology and crystal composition. The electrochemical catalytic ability of the Ti/Ta₂O₅-IrO₂ electrode was investigated using LSV and CV tests. The electrochemical degradation of tetracycline (TC) in water with a Ti/Ta₂O₅-IrO₂ anode was investigated. The main influence factors, such as current density (2.5–10 mA/cm²), electrode spacing (20–40 mm), initial TC concentration (20–80 mg/L) and initial solution pH (4.74–9.48) were analyzed in detail and their influences on reaction kinetics was summed up. The removal rate increased along with the increasing current density, decreasing initial TC concentration and decreasing of electrode distance under the experimental conditions. The optimum pH was 4.74. UV–vis, total organic carbon (TOC) and high-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses were used to reveal the mechanism of TC degradation. Nine main intermediates were identified, and the degradation pathways were proposed. A new insight has been postulated for the safe and efficient degradation of TC using the Ti/Ta₂O₅-IrO₂ electrode.     

On the Sintering Behavior of Nb2O5 and Ta2O5 Mixed Oxide Powders

A mixed oxide system consisting of Nb₂O₅ and Ta₂O_5, was subjected to annealing in air/hydrogen up to 950 °C for 1–4 h to study its sintering behavior. The thermogravimetric–differential scanning calorimetry (TGA–DSC) thermograms indicated the formation of multiple endothermic peaks at temperatures higher than 925 °C. Subsequently, a 30% Ta₂O₅ and 70% Nb₂O₅ (mol%) pellet resulted in good sintering behavior at both 900 and 950 °C. The scanning electron microscope (SEM) images corroborated these observations with necking and particle coarsening. The sintered pellets contained a 20.4 and 20.8% mixed oxide (Nb₄Ta₂O₁₅) phase, along with Ta₂O₅ and Nb₂O₅, at both 900 and 950 °C, indicating the possibility of the formation of a solid solution phase. In situ high-temperature X-ray diffraction (XRD) scans also confirmed the formation of the ternary oxide phase at 6 and 19.8% at 890 and 950 °C, respectively. The Hume–Rothery rules could explain the good sintering behavior of the Ta₂O₅ and Nb₂O₅ mixed oxides. An oxide composition of 30% Ta₂O₅ and 70% Nb₂O₅ (mol%) and a sintering temperature of 950 °C appeared adequate for fabricating well-sintered oxide precursors for subsequent electrochemical polarization studies in fused salts.     

Phase Transition and Coefficients of Thermal Expansion in Al2−xInxW3O12 (0.2 ≤ x ≤ 1)

Materials from theA₂M₃O₁₂ family are known for their extensive chemical versatility while preserving the polyhedral-corner-shared orthorhombic crystal system, as well as for their consequent unusual thermal expansion, varying from negative and near-zero to slightly positive. The rarest are near-zero thermal expansion materials, which are of paramount importance in thermal shock resistance applications. Ceramic materials with chemistry Al_2−xIn_xW₃O₁₂ (x = 0.2–1.0) were synthesized using a modified reverse-strike co-precipitation method and prepared into solid specimens using traditional ceramic sintering. The resulting materials were characterized by X-ray powder diffraction (ambient and in situ high temperatures), differential scanning calorimetry and dilatometry to delineate thermal expansion, phase transitions and crystal structures. It was found that the x = 0.2 composition had the lowest thermal expansion, 1.88 × 10⁻⁶ K⁻¹, which was still higher than the end member Al₂W₃O₁₂ for the chemical series. Furthermore, the AlInW₃O₁₂ was monoclinic phase at room temperature and transformed to the orthorhombic form at ca. 200 °C, in contrast with previous reports. Interestingly, the x = 0.2, x = 0.4 and x = 0.7 materials did not exhibit the expected orthorhombic-to-monoclinic phase transition as observed for the other compositions, and hence did not follow the expected Vegard-like relationship associated with the electronegativity rule. Overall, compositions within the Al_2−xIn_xW₃O₁₂ family should not be considered candidates for high thermal shock applications that would require near-zero thermal expansion properties.     

The Effect of Ca Dopant on the Electrical and Dielectric Properties of BaTi4O9 Sintered Ceramics

The current research examines the impact of Ca²⁺ substitution on the phase and electrical properties of (Ba_1−xCa_x)Ti₄O₉, (x = 0.0, 0.3, 0.6, and 0.9) sintered pellets synthesized by solid-state reaction method. The as-synthesized samples were analyzed using X-ray diffraction (XRD) and impedance spectroscopy. The emergence of orthorhombic phase fit into space group Pnmm was revealed by XRD, and the addition of Ca resulted in a considerable shift in grain size. Dielectric properties were determined using an impedance spectroscopy in a wide frequency range from 1MHz to 3 GHz. The dielectric properties i.e., dielectric constant (ε_r) and dielectric loss (tanσ), were measured at 3 GHz frequency. The frequency-dependent parameters such as conductivity, dielectric constant, and dielectric loss indicated that the relaxation process is a Maxwell–Wagner type of interfacial polarization. The improved dielectric properties and low energy loss have made (Ba_1−xCa_x)Ti₄O₉ a prominent energy storage material. This study provides the possibility to improve its dielectric properties and reduce energy loss, making it an excellent energy storage material.     

Study on Crystallization Process of Li2O–Al2O3–SiO2 Glass-Ceramics Based on In Situ Analysis

In this paper, we used differential scanning calorimetry (DSC), high-temperature X-ray diffraction (HT-XRD), and confocal scanning laser microscopy (CSLM) to investigate the Li₂O–Al₂O_3–SiO₂ glass crystallization process. At 943 K, lithium disilicate (Li₂Si₂O₅) phase crystals began to precipitate in the Li₂O–Al₂O₃–SiO₂ glass with a crystal size of 50–70 nm. At the temperature of 1009 K, petalite (LiAlSi₄O₁₀) crystals began to precipitate in the vitreous phase, forming composite spherical crystals of LiAlSi₄O₁₀ and Li₂Si₂O₅ with size in the range of 90–130 nm. Furthermore, the Kissinger method and KAS method of the JMAK model were used to calculate the crystallization activation energy and the Avrami index “n”. It was found that the precipitation mechanism of the two kinds of crystals is whole crystallization; accordingly, the selection of crystallization heat treatment system was guided to determine the nucleation and crystallization temperature.     

Fe–Doped TiO2–Carbonized Medium–Density Fiberboard for Photodegradation of Methylene Blue under Visible Light

Fe–doped titanium dioxide–carbonized medium–density fiberboard (Fe/TiO₂–cMDF) was evaluated for the photodegradation of methylene blue (MB) under a Blue (450 nm) light emitting diode (LED) module (6 W) and commercial LED (450 nm + 570 nm) bulbs (8 W, 12 W). Adsorption under daylight/dark conditions (three cycles each) and photodegradation (five cycles) were separately conducted. Photodegradation under Blue LED followed pseudo-second-order kinetics while photodegradation under commercial LED bulbs followed pseudo-first-order kinetics. Photodegradation rate constants were corrected by subtracting the adsorption rate constant except on the Blue LED experiment due to their difference in kinetics. For 8 W LED, the rate constants remained consistent at ~11.0 × 10⁻³/h. For 12 W LED, the rate constant for the first cycle was found to have the fastest photodegradation performance at 41.4 × 10⁻³/h. After the first cycle, the rate constants for the second to fifth cycle remained consistent at ~28.5 × 10⁻³/h. The energy supplied by Blue LED or commercial LEDs was sufficient for the bandgap energy requirement of Fe/TiO₂–cMDF at 2.60 eV. Consequently, Fe/TiO₂–cMDF was considered as a potential wood-based composite for the continuous treatment of dye wastewater under visible light.     

Growth and Investigation of Annealing Effects on Ternary Cd1−xMgxO Nanocomposit Thin Films

Thin films of Cd_1−xMg_xO (CdMgO) (0 ≤ x ≤ 1) were investigated by depositing the films on glass substrates using the co-evaporation technique. The structural, surface morphological, optical, and electrical characteristics of these films were studied as a function of Mg content after annealing at 350 °C. The XRD analysis showed that the deposited films had an amorphous nature. The grain size of the films reduced as the Mg concentration increased, as evidenced by the surface morphology, and EDAX supported the existence of Mg content. It was observed that as the films were annealed, the transmittance of the CdMgO films saw an increase of up to 85%. The blue shift of the absorption edge was observed by the increase of Mg content, which was useful for enhancing the efficiency of solar cells. The optical band gap increased from 2.45 to 6.02 eV as the Mg content increased. With increased Mg content, the refractive index reduced from 2.49 to 1.735, and electrical resistivity increased from 535 Ω cm to 1.57 × 10⁶ Ω cm.     

The Reaction Products of the Al–Nb–B2O3–CuO System in an Al 6063 Alloy Melt and Their Influence on the Alloy’s Structure and Characteristics

To meet aero-engine aluminum skirt requirements, an experiment was carried out using Al–Nb–B₂O₃–CuO as the reaction system and a 6063 aluminum alloy melt as the reaction medium for a contact reaction, and 6063 aluminum matrix composites containing in situ particles were prepared with the near-liquid-phase line-casting method after the reaction was completed. The effects of the reactant molar ratio and the preheating temperature on the in situ reaction process and products were explored in order to determine the influence of in situ-reaction-product features on the organization and the qualities of the composites. Thermodynamic calculations, DSC analysis, and experiments revealed that the reaction could continue when the molar ratio of the reactants of Al–Nb–B₂O₃–CuO was 6:1:1:1.5. A kinetic study revealed that the Al thermal reaction in the system produced Al₂O₃ and [B], and the [B] atoms interacted with Nb to generate NbB₂. With increasing temperature, the interaction between the Nb and the AlB₂ produced hexagonal NbB₂ particles with an average longitudinal size of 1 μm and subspherical Al₂O₃ particles with an average longitudinal size of 0.2 μm. The microstructure of the composites was reasonably fine, with an estimated equiaxed crystal size of around 22 μm, a tensile strength of 170 MPa, a yield strength of 135 MPa, an elongation of 13.4%, and a fracture energy of 17.05 × 10⁵ KJ/m³, with a content of 2.3 wt% complex-phase particles. When compared to the matrix alloy without addition, the NbB₂ and Al₂O₃ particles produced by the in situ reaction had a significant refinement effect on the microstructure of the alloy, and the plasticity of the composite in the as-cast state was improved while maintaining higher strength and better overall mechanical properties, allowing for industrial mass production.     

Cobalt Minimisation in Violet Co3P2O8 Pigment

This study considers the limitations of cobalt violet orthophosphate, Co₃P₂O₈, in the ceramic industry due to its large amount of cobalt. Mg_xCo_3−xP₂O₈ (0 ≤ x ≤ 3) solid solutions with the stable Co₃P₂O₈ structure were synthesised via the chemical coprecipitation method. The formation of solid solutions between the isostructural Co₃P₂O₈ and Mg₃P₂O₈ compounds decreased the toxically large amount of cobalt in this inorganic pigment and increased the melting point to a temperature higher than 1200 °C when x ≥ 1.5. Co₃P₂O₈ melted at 1160 °C, and compositions with x ≥ 1.5 were stable between 800 and 1200 °C. The substitution of Co(II) with Mg(II) decreased the toxicity of these materials and decreased their price; hence, the interest of these materials for the ceramic industry is greater. An interesting purple colour with a* = 31.6 and b* = −24.2 was obtained from a powdered Mg_2.5Co_0.5P₂O₈ composition fired at 1200 °C. It considerably reduced the amount of cobalt, thus improving the colour of the Co₃P₂O₈ pigment (a* = 16.2 and b* = −20.1 at 1000 °C). Co₃P₂O₈ is classified as an inorganic pigment (DCMA-8-11-1), and the solid solutions prepared were also inorganic pigments when unglazed. When introducing 3% of the sample (pigment) together with enamel, spreading the mixture on a ceramic support and calcining the whole in an electric oven, a colour change from violet to blue was observed due to the change in the local environment of Co(II), which could be seen in the UVV spectra of the glazed samples with the displacement of the bands towards higher wavelengths and with the appearance of a new band assigned to tetrahedral Co(II). This blue colour was also obtained with Co₂SiO₄, MgCoSiO₄ or Co₃P₂O₈ pigments containing a greater amount of cobalt.     

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

Al₂O₃-CaO-Cr₂O₃ castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated the relative reactivity of analogous Cr(III) phases such as Cr₂O₃, (Al_1−xCr_x)₂O₃ and in situ Cr(III) solid solution with the calcium aluminate cement under an oxidizing atmosphere at various temperatures. The aim is to comprehend the relative Cr(VI) generation in the low-cement castables (Al₂O₃-CaO-Cr₂O₃-O₂ system) and achieve an environment-friendly application. The solid-state reactions and Cr(VI) formation were investigated using powder XRD, SEM, and leaching tests. Compared to Cr₂O₃, the stability of (Al_1−xCr_x)₂O₃ against CAC was much higher, which improved gradually with the concentration of Al₂O₃ in (Al_1−xCr_x)₂O₃. The substitution of Cr₂O₃ with (Al_1−xCr_x)₂O₃ in the Al₂O₃-CaO-Cr₂O₃ castables could completely inhibit the formation of Cr(VI) compound CaCrO₄ at 500–1100 °C and could drastically suppress Ca₄Al₆CrO₁₆ generation at 900 to 1300 °C. The Cr(VI) reduction amounting up to 98.1% could be achieved by replacing Cr₂O₃ with (Al_1−xCr_x)₂O₃ solid solution. However, in situ stabilized Cr(III) phases as a mixture of (Al_1−xCr_x)₂O₃ and Ca(Al_12−xCr_x)O₁₉ solid solution hardly reveal any reoxidation. Moreover, the CA₆ was much more stable than CA and CA₂, and it did not participate in any chemical reaction with (Al_1−xCr_x)₂O₃ solid solution.     

Hf1−xSixO2 Nanocomposite Coatings Prepared by Ion-Assisted Co-Evaporation Process for Low-Loss and High-LIDT Optics

Hf_1−xSi_xO₂ nanocomposites with different SiO₂ doping ratios were synthesized using an ion-assisted co-evaporation process to achieve dense amorphous Hf_1−xSi_xO₂ coatings with low loss and a high laser-induced damage threshold (LIDT). The results showed that the Hf_1−xSi_xO₂ nanocomposites (x ≥ 0.20) exhibited excellent comprehensive performance with a wide band gap and a dense amorphous microstructure. High-temperature annealing was carried out to ensure better stoichiometry and lower absorption. Precipitation and regrowth of HfO₂ grains were observed from 400 °C to 600 °C during annealing of the Hf_0.80Si_0.20O₂ nanocomposites, resulting in excessive surface roughness. A phenomenological model was proposed to explain the phenomenon. The Hf_1−xSi_xO₂ nanocomposites (x = 0.3 and 0.4) maintained a dense amorphous structure with low absorption after annealing. Finally, a 1064-nm Hf_0.70Si_0.30O₂/SiO₂ high-performance reflector was prepared and achieved low optical loss (15.1 ppm) and a high LIDT (67 J/cm²).