Ceramics

Microsilica recovered from silicon-production off-gases offers a secondary feedstock for silica-based ceramics. This study evaluates its consolidation by spark plasma sintering (SPS), with purchased commercial nanosilica serving as a reference. Both feedstocks were processed at a monitored die temperature of 1300 °C, 50 MPa, and a 10 min hold. Characterization combined powder microscopy, qualitative X-ray diffraction, hydrostatic weighing, ultrasonic contact impedance (UCI), and axial compression. Mean hydrostatic densities were 2.246 ± 0.007 and 2.254 ± 0.007 g·cm⁻³ for microsilica and nanosilica, respectively. Mean maximum nominal stresses were 208 ± 13 and 188 ± 6 MPa for Ø14 × 2 mm disks; values are mean ± sample standard deviation (n = 3 per feedstock). The microsilica specimens exhibited a 10.3% higher mean maximum nominal stress under this loading configuration and higher comparative UCI indications. Both cooled ceramics showed reflections consistent with α-cristobalite. The study extends earlier waste-processing work through a comparison with commercial nanosilica that relates powder characteristics and phase identity to replicate property measurements under a common SPS schedule. The results demonstrate the material feasibility of consolidating microsilica waste into coherent ceramic bodies and support further development of this utilization route.

The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of an EFG-grown (−201) β-Ga₂O₃ single crystal were recorded at 7 and 300 K at the FinEstBeAMS beamline of the MAX IV Laboratory. Excitation–emission maps and fixed-wavelength PLE profiles covered 4.50–10.50 eV at both temperatures. Each temperature series was normalized to its own 5.00 eV intensity and, alternatively, to its own maximum; the reported ratios therefore describe excitation dependence within one series and not an absolute difference in luminescence yield between temperatures. At 7 K, integrated emission at 10.50 eV retains 95.4% of its 5.00 eV value and 89.2% of its maximum. At 300 K, the PLE half-height is 4.55 eV, and the maximum occurs at 4.75–4.80 eV, followed by a decrease to 2.26% of the 5.00 eV value and 2.03% of the maximum at 10.50 eV. Room-temperature ellipsometry on the same factory-polished face places the PLE rise in the rapidly increasing absorption region and yields a penetration depth of approximately 0.24 μm near the PLE half-height and 37 nm at 5.90 eV. A constrained depth-dependent calculation does not reproduce the full decline, so surface capture is retained as one possible pathway rather than an established mechanism. The emission is described by the same effective bands at 3.55, 3.37 and 3.07 eV used in the preceding laser study. Their balance is nearly constant at 7 K, whereas the low-energy spectral weight increases at 300 K under deep-VUV excitation. These spectra provide quantitative reference profiles for energy conversion and carrier capture in β-Ga₂O₃.

Phosphate glasses with the compositions 60P₂O₅–15ZnO–15CaO–10Li₂O (PZCL) and 60P₂O₅–15ZnO–15CaO–10V₂O₅ (PZCV) (mol%, expressed as oxides) were synthesized by the melt-quenching method. The prepared glasses were characterized by using X-ray powder diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). X-ray diffraction shows only broad diffuse halos without Bragg reflections, indicating that both glasses are X-ray amorphous. Raman analysis confirms that PZCL behaves as a typical alkali-modified ultraphosphate glass containing Q³ and Q² units, whereas PZCV contains characteristic V–O vibrational modes indicating that vanadate groups are integrated into the phosphate backbone. SEM observations reveal smooth surfaces at low magnification for both glasses; at higher magnification, PZCV shows a compact and homogeneous surface with fine, uniformly dispersed granules, whereas PZCL displays a more textured surface with agglomerates and plate-like features. EIS analysis using the Havriliak–Negami model reveals that the free-charge carrier contribution appears as a step in M′(ω,T) and a peak in M″(ω,T), allowing a clear distinction between conductivity relaxation and interfacial polarization or dipolar effects, with conductivity derived from the M″(ω,T) peak frequency. PZCV shows dc conductivity approximately one order of magnitude higher than PZCL (1.5 × 10⁻⁹ vs. 1.8 × 10⁻¹⁰ S·cm⁻¹ at 120 °C). The temperature dependence follows Arrhenius behavior, with activation energies of about 0.89 eV for PZCV and 1.04 eV for PZCL. The electrode polarization observed at low frequencies with ion-blocking gold electrodes indicates a significant ionic contribution in both glasses, although a polaronic (V⁴⁺/V⁵⁺) contribution to the conductivity of PZCV cannot be excluded. Capacitance analysis reveals a slight increase with temperature for both samples, with PZCV consistently showing higher values (~7 pF) than PZCL (~5 pF). Although the absolute conductivities remain far below those required for practical solid electrolytes, these results clarify how the replacement of Li₂O by V₂O₅ modifies charge transport and dielectric relaxation in P₂O₅-rich Zn–Ca phosphate glasses.