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The aqueous reprocessing of spent nuclear fuel generates a considerable amount of plutonium alongside contaminated stainless steel, necessitating meticulous handling for safe decommission and long‐term management. The present work investigated the co‐immobilization of CeO2 (as an inactive surrogate for PuO2) with metallic Fe and Cr (representing a simplified stainless steel) within a zirconolite ceramic wasteform, nominally targeting Ca1−xCexZrTi2−2xFexCrxO7. After sintering at 1400°C under an air atmosphere, the zirconolite phase constituted 90.8–95.1 wt.% of the product across the solid solution range of 0.05 ≤ x ≤ 0.25, alongside perovskite and baddeleyite secondary phases in varying proportion; no evidence of the unincorporated CeO2 or metallic and oxidized Fe or Cr were identified. Above x = 0.30 CeO2 was detected inferring, the solubility limit was reached. A polytype transformation from zirconolite 2M to 3T was confirmed by X‐ray diffraction and selected area electron diffraction results, with the relative fraction of the 3T phase gradually increasing to 49.5 wt.% at x = 0.30. Deconvolution of X‐ray photoelectron spectroscopy data revealed the partial reduction of Ce4+–Ce3+, whereas Fe and Cr species maintained trivalent, in agreement with the targeted substitution scheme. Benefitting from the excellent chemical flexibility of zirconolite structured compounds, the co‐immobilization approach may be an effective disposal pathway for Pu‐containing wastes and contaminated stainless steel residues. [ABSTRACT FROM AUTHOR]

Investigating the microwave dielectric properties of ceramics prepared through the conventional solid-state route, such as x[(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-(1−x)Ca0.6(La0.9Y0.1)0.2667TiO3, reveals notable characteristics. [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02 shows a permittivity (εr) of approximately 20, a high quality factor (Q × f) ranging between 250,000 and 560,000 GHz, and a temperature coefficient of resonant frequency (τf) of approximately −65 ppm/°C. To enhance the temperature stability, Ca0.6(La0.9Y0.1)0.2667TiO3 featuring a τf value of +374 ppm/°C was incorporated into the [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02 composition. τf demonstrated an increase with rising Ca0.6(La0.9Y0.1)0.2667TiO3 content, reaching zero at x = 0.95. A ceramic composition of 0.95[(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-0.05Ca0.6(La0.9Y0.1)0.2667TiO3, incorporating 3wt.% BaCu(B2O5) as sintering aids, exhibited outstanding microwave dielectric properties: εr~22.5, Q × f~195,000 (at 9 GHz), and τf~0.1ppm/°C, with a sintering temperature at 950 °C. This material is proposed as a prospective candidate for 6G band components and GPS antennas. [ABSTRACT FROM AUTHOR]

This study prepared ultralow electron-loss perovskites with spinel-like structures via a solid-state reaction. The (Mg0.95Co0.05)2(Ti0.95Sn0.05)O4 (MCTS) ceramic exhibited approximate values for ultrahigh quality factor, permittivity, and negative temperature coefficient (τf) of 310,000 GHz, 14.25, and −48.1 ppm/oC, respectively. To bring the τf closer to zero, a trace amount of (Ca0.95Sr0.05)(Ti0.97Sn0.03)O3 (CSTS) perovskite was added to MCTS during ceramic manufacturing. CSTS exhibited a permittivity of 92 and a large positive τf value of 810 ppm/°C. A 0.92MCTS–0.08CSTS hybrid ceramic sintered at 1325°C achieved remarkable microwave dielectric properties of εr ~18.42, Q×f ~ 237,000 GHz and τf ~3.72 ppm/°C. This mixed ceramic has significant potential for applications in manufacturing microwave devices. [ABSTRACT FROM AUTHOR]

In this study, we used solid-state synthesis to prepare Ba[(ZnxCo1−x)1/3(Nb0.5Ta0.5)2/3]O3 microwave ceramics for mobile communications. Compared with Ba[Zn1/3(Nb0.5Ta0.5)2/3]O3, in the prepared materials, Co2+ substitution with Zn2+ improved the Q × f value and enabled densification and sintering at a lower temperature. We used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the obtained microstructure. Ba[(ZnxCo1−x)1/3(Nb0.5Ta0.5)2/3]O3 was found to have a 1:2 ordered hexagonal structure, and its Q × f value increased with the increase in sintering temperature. In this work, excellent microwave dielectric properties—τf = −0.7 ppm/°C, εr = 34.5, and Q × f = 110,000 GHz—were obtained by sintering Ba[(Zn0.3Co0.7)1/3(Nb0.5Ta0.5)2/3]O3 at 1400 °C for 5 h. [ABSTRACT FROM AUTHOR]

The crystallization, microstructure analysis, and sintering behavior, microwave properties of (Mg0.95Co0.05)2(Ti1−xSnx)O4 ceramics, processed with raw powders of MgO, CoO, SnO2, and TiO2 via the conventional solid-state method are investigated. X-ray diffraction and X-ray spectroscopy analyses showed that the crystal structure of these samples was spinel-type. The microstructure with the substitution amount of Sn4+ and the dielectric performances of the (Mg0.95Co0.05)2(Ti1−xSnx)O4 ceramics were also explored. The (Mg0.95Co0.05)2(Ti1−xSnx)O4 ceramic could be sintered at 1350 °C, and the microwave dielectric performance was found to be strongly correlated with the sintering temperature. A maximum quality factor (Q×f) value of 330,000 (GHz), dielectric constant (εr) of 14.75, and temperature coefficient (τf) of −47.5 ppm/°C were achieved for samples sintered at 1350 °C for 4 h. (Mg0.95Co0.05)2(Ti0.97Sn0.03)O4 material system shows high potential for applications of high frequency-selection components in satellite communication and 5th Generation Mobile Communication Technology wireless telecommunication systems. [ABSTRACT FROM AUTHOR]