Milan Parchovianský

Tb/Yb‐codoped Li‐containing oxyfluoride glasses (OxGs) with compositions 47SiO ₂ ‐19Al ₂ O ₃ ‐17Li ₂ O‐9LiF‐(8‐x‐y)YF ₃ ‐xTbF ₃ ‐yYbF ₃ (x = 0.5–2; y = 1–7) were synthesized via melt‐quenching method to study concentration‐dependent Tb ³⁺ → Yb ³⁺ energy transfer and up‐conversion (UC) behavior. Transparent glass‐ceramics were subsequently produced by hot pressing, yielding dense materials with mixed amorphous–crystalline phases. The glasses exhibit good thermal stability ( T _g = 510°C–530°C, Δ T ≈ 100°C) and a mixed oxide–fluoride network with homogeneous fluorine distribution. ²⁷ Al NMR of the undoped glass confirms the stabilization and predominance of tetrahedrally coordinated, corner‐sharing [AlO ₄ ] units, while the ¹⁹ F NMR reveals the presence of fluorine in different environments. Photoluminescence results show that under 980 nm near‐infrared laser excitation, both glasses and glass‐ceramics exhibit intense green Tb ³⁺ : ⁵ D ₄ → ⁷ F _J (J = 6, 5, 4, 3) UC luminescence due to cooperative energy transfer (CET) from two Yb ³⁺ ions to one Tb ³⁺ ion. In contrast, 351 nm excitation induces near‐infrared quantum‐cutting down‐conversion emission corresponding to Yb ³⁺ : ² F _5/2 → ² F _7/2 transition, arising from the CET process from one Tb ³⁺ ion to two Yb ³⁺ ions. These results demonstrate efficient bidirectional energy transfer in the Tb ³⁺ /Yb ³⁺ system and highlight the potential of these materials for photonic applications.

This study presents a multicomponent-engineering strategy to tailor the thermophysical and mechanical properties of high-entropy rare-earth A2B2O7 ceramics by tuning the cationic radius ratio (rA/rB), size disorder (δR), and mass disorder (δM). A series of compositions incorporating multiple rare-earth A-site cations and mixed B-site cations (Zr, Hf, Ce) were synthesized via solid-state reaction and high-temperature sintering. A systematic structural transition from disordered fluorite to ordered pyrochlore was confirmed by X-ray diffraction, Rietveld refinement, Raman spectroscopy, and X-ray photoelectron spectroscopy, with intermediate compositions exhibiting dual-phase coexistence. Structural disorder, governed by rA/rB and δR, plays a dominant role in oxygen vacancy formation and phonon scattering. Compositions with intermediate rA/rB (e.g., C#7) exhibit ultra-low thermal conductivity (as low as 1.09 W·m-1·K-1 at 1000 ℃), accompanied by reduced phonon mean free paths approaching the amorphous limit. The average thermal expansion coefficients between 500–850 ℃ range from 10.56 to 12.45 × 10-6 K-1, with C#8 showing a favorable balance of low thermal conductivity and relatively high TEC (11.7 × 10-6 K-1). Increased structural ordering and stronger B–O bonding enhance hardness and fracture toughness, with a maximum value of 2.75 MPa·m1/2. These findings highlight the critical role of coupled compositional disorder and phase evolution in tailoring functional properties of high-entropy oxides.

This work demonstrates the capability to crystallize YAG via femtosecond pulsed laser. Challenges in using melt‐quench glass are shown to restrict glass composition and have not yielded YAG via femtosecond laser crystallization. An alternative glass‐making technique was used to fabricate a range of compositions not otherwise possible. Glasses of YAG with added silica in the range of 0–20 mol% were tested under the laser to explore the allowable deviation from stoichiometric YAG. Raman spectroscopy and Electron backscatter diffraction indicated successful fabrication of YAG, and usage of combined excitation emission spectroscopy (CEES) allowed probing of erbium doped compositions.

This work focuses on the fabrication of lanthanum cerate (La₂Ce₂O₇, LC) powders via two chemical routes: modified Pechini sol-gel method and solid-state synthesis. The synthesized LC powders were heat treated in the temperature range of 1000–1400 °C for 6 h and investigated as a material for thermal barrier coating (TBC) applications. For this purpose, the powder morphology, chemical composition, crystal structure and thermal stability were studied. Scanning electron microscopy (SEM) of the synthesized powders revealed an agglomerated structure consisting of fine and uniformly distributed grains. Energy-dispersive X-ray spectroscopy (EDXS) indicated that the chemical compositions of the LC powders were similar to the stoichiometric ratio of La₂Ce₂O₇. A cubic fluorite structure was observed by X-ray diffraction analysis (XRD) after calcining the LC powder prepared by solid-state synthesis at 1300 °C. In contrast, there was always a fluorite structure in the LC powder synthesized by the Pechini sol-gel method after heat treatment over the entire temperature range. The thermal behavior of the LC powders was analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) in the temperature range of 25–1300 °C. Neither an obvious mass change nor a visible energy change was observed within the tested temperature range, indicating high phase stability of the LC powder and its suitability for TBC applications. Spheroidization on the prepared LC powders was also investigated, revealing that powder size and morphology had a significant impact on the spheroidization efficiency.

In this work, La₂Ce₂O₇-yttria-stabilized zirconia (LC-YSZ) composites with different weight fractions of YSZ (40–70 wt.%) were prepared by hot pressing at 1400 °C and investigated as a material for thermal barrier-coating (TBC) applications. For this purpose, the effect of YSZ addition on the phase composition, microstructure, mechanical performance and thermal behavior was studied. X-ray diffraction analysis showed that the LC-YSZ composites were mainly composed of a cubic ZrO₂ and La₂O₃-CeO₂-ZrO₂ solid solution with a pyrochlore structure, indicating that the reaction between LC and YSZ took place during hot pressing. Scanning electron microscopy revealed the high microstructural stability of the prepared composites, as the pore formation was significantly controlled and a high relative density (>97%) was obtained. The microstructure of LC-YSZ bulk samples was relatively fine-grained, with an average grain size below or very close to 1 µm. YSZ doping improved the Vickers hardness of the LC-YSZ composites; the highest hardness, with value of 12 ± 0.62 GPa, was achieved for the composite containing 70 wt.% of YSZ. The fracture toughness of LC-YSZ composites was in the range from 2.13 to 2.5 MPa·m^1/2. No statistically significant difference in heat capacity or thermal conductivity was found between the composites with different content of YSZ. The results showed that LC-YSZ composites have relatively low thermal conductivities from room temperature (1.5–1.8 W·m⁻¹·K⁻¹) up to 1000 °C (2.5–3.0 W·m⁻¹·K⁻¹). This indicates that the prepared LC-YSZ composite materials are promising candidates for TBC applications.

Polysilazane-based double layer composite coatings consisting of a polymer-derived ceramic (PDC) bond-coat and a PDC top-coat that contains ceramic passive and glass fillers were developed. To investigate the environmental protection ability of the prepared coatings, quasi-dynamic corrosion tests under hydrothermal conditions were conducted at 200 °C for 48–192 h. The tested PDC coatings exhibited significant mass loss of up to 2.25 mg/cm² after 192 h of corrosion tests, which was attributed to the leaching of elements from the PDC coatings to the corrosion medium. Analysis of corrosion solutions by inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed the presence of Ba, Al, Si, Y, Zr, and Cr, the main component of the steel substrate, in the corrosion medium. Scanning electron microscopy (SEM) of the corroded surfaces revealed randomly distributed globular crystallites approximately 3.5 µm in diameter. Energy-dispersive X-ray spectroscopy (EDXS) of the precipitates showed the presence of Ba, Al, Si, and O. The predominant phases detected after corrosion tests by X-ray powder diffraction analysis (XRD) were monoclinic and cubic ZrO₂, originating from the used passive fillers. In addition, the crystalline phase of BaAl₂Si₂O₈ was also identified, which is in accordance with the results of EDXS analysis of the precipitates formed on the coating surface.

Sintering by viscous flow in a “kinetic window” between T _g and T _x temperatures was used to prepare bulk glass/glass‐ceramic luminescent materials from rapidly quenched glass microspheres in the system Y ₂ O ₃ –Al ₂ O ₃ doped with Ce ³⁺ ions. The glass microspheres were prepared from sol–gel synthesized precursor powders in a high‐temperature methane‐oxygen flame. The crystallization of the glasses was analyzed using differential scanning calorimetry and high‐temperature X‐ray diffraction. The crystallization behavior of quenched glass microspheres was found to be strongly dependent on glass composition. The glass microspheres were consolidated into bulk material by hot‐pressing technique at a temperature of up to 1100℃ with the applied pressure 40MPa. The optimized time‐temperature‐pressure regime enables the preparation of bulk glass, and glass‐ceramic with a high fraction of crystalline Ce ³⁺ ‐doped YAG phase embedded in the Al ₂ O ₃ ‐enriched glass matrix. The glass/glass‐ceramics emit blue/yellow light with high intensity under excitation in UV and/or blue spectral region.

Although glass recycling is considered to be a default method for glass waste management, fine fractions of container soda‐lime glass, or cullet of other compositions are still landfilled. This happens despite existing alternatives. Success could lie in advanced upcycled products that bring higher economic motivation for the implementation in industry, but these are often connected to alternative ways of product synthesis. We provide an example of waste glass upcycling by the preparation of glass microspheres (GM) from specialty low‐sodium alumino borosilicate‐based glasses via flame synthesis (FS). GM and the precursors, either from colorless medical vials or glass fibers, were characterized by scanning electron microscopy (SEM), simultaneous thermal analysis coupled with differential thermal analysis (STA‐DTA), and image analysis. A dynamic corrosion test was performed and evaluated via ion‐coupled plasma with optical emission spectroscopy (ICP‐OES) to observe corrosion kinetics products. FS has proved to be a fast method of waste glass processing into GM. This article, besides the characterization of the starting material and final products, also suggests the possibility of processing for other landfilled waste glasses and also discusses the manufacturing of GM for water filters and fillers for polymers.