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Using a solid-state reaction strategy, nominal Li3TiO3F oxyfluorides ceramics were fabricated, and its sintering behavior, microstructure, phase assemblages, as well as microwave dielectric performances were all investigated. The main phase of Li3TiO3F with cubic structures accompanied with small amounts of the LiF or Li2TiO3 secondary phase was identified by XRD analysis. SEM analysis showed that a uniform and dense microstructure was obtained for 750 °C-sintered samples. The dielectric constant (εr) and quality factor (Q × f) were found to be strongly correlated with porosity and grain size distribution, whereas the temperature coefficient of resonance frequency (τf) was mainly dominated by the phase assemblages. In particular, the 750 °C-sintered Li3TiO3F samples exhibited good microwave dielectric performances: εr = 18, Q × f = 57,300 GHz (under 9.2 GHz), τf = −43.0 ppm/°C. [ABSTRACT FROM AUTHOR]

(1 − x)Li3Mg2SbO6-xBa3(VO4)2 (0.0 ≤ x ≤ 0.20, LMS-BV) composite ceramics were prepared via a conventional solid-state reaction method. The microstructure and microwave dielectric properties were investigated. Li3Mg2SbO6 and Ba3(VO4)2 phases coexisted well in the range of 0.1 ≤ x ≤ 0.20. Adding Ba3(VO4)2 to Li3Mg2SbO6 not only inhibited the fragility but also improved the thermal stability of Li3Mg2SbO6-based ceramics. With the increase of x value, the εr and τf values of (1 − x)LMS-xBV composite ceramics gradually increased, while its Qxf value declined. Typically, the 0.9LMS-0.1BV composite ceramics sintered at 1200 °C for 5 h demonstrated good microwave dielectric properties: εr = 10.9, Qxf = 45,100 GHz (at ~ 10.4 GHz), τf = 2.4 ppm/°C. [ABSTRACT FROM AUTHOR]

(1−x)Ca 5 Mg 4 (VO 4 ) 6 -xBa 3 (VO 4 ) 2 (0.5 ≤ x ≤ 0.7) ceramics were fabricated via the conventional solid-state reaction method. The phase composition, microstructure, and compatibility with silver were investigated using X-ray diffraction, Raman spectra and Scanning electron microscopy. The results confirmed that Ca 5 Mg 4 (VO 4 ) 6 and Ba 3 (VO 4 ) 2 crystal phases can be well coexisted in the sintered ceramics. The temperature coefficient of resonant frequency could be tuned by the volume mixture rule of Ca 5 Mg 4 (VO 4 ) 6 and Ba 3 (VO 4 ) 2 . As for the addition of Ba 3 (VO 4 ) 2 , the ε r showed to increase, while the Qxf declined. In particular, the 0.35Ca 5 Mg 4 (VO 4 ) 6 -0.65Ba 3 (VO 4 ) 2 composite ceramics sintered at 900 °C for 5 h showed excellent combinational microwave dielectric properties: ε r = 11.9, Qxf = 35 000 GHz, and τ f = −2 ppm/°C, which also exhibited good chemical compatibility with silver. [ABSTRACT FROM AUTHOR]

Network structures assembled from α-Fe 2 O 3 nanosheets with exposed {104} facets were successfully prepared by heating Fe(NO 3 ) 3 solution containing polyvinylpyrrolidone (PVP) in air. The α-Fe 2 O 3 nanosheet-based network structures demonstrate significantly higher response to ethanol and triethylamine than α-Fe 2 O 3 commercial powders. The excellent sensing performances can be ascribed to the exposed (104) facet terminated with Fe atoms. A concept of the unsaturated Fe atoms serving as the sensing reaction active sites is thus proposed, and the sensing reaction mechanism is described at the atomic and molecular level for the first time in detail. The concept of the surface metal atoms with dangling bonds serving as active sites can deepen understanding of the sensing and other catalytic reaction mechanisms and provides new insight into the design and fabrication of highly efficient sensing materials, catalysts, and photoelectronic devices.

Hydrogenation is successfully employed to improve sensing performances of the gas sensors based on TiO 2 nanosheets with exposed {001} facets for the first time. The hydrogenated TiO 2 nanosheets show a significantly higher response toward ethanol, acetone, triethylamine, or formaldehyde than the samples without hydrogenation, and the response further increases with an increase of the hydrogenation temperature. The excellent sensing performances are ascribed to an increase of the density of unsaturated Ti 5c atoms on the {001} surface resulting from the hydrogenation process. The unsaturated Ti 5c atoms are considered to serve as sensing reaction active sites. They can generate noncontributing (free) electrons and adsorb oxygen molecules, and the detailed sensing mechanism is described at atomic and molecule level. The hydrogenated strategy may be employed to enhance the sensing performances of other metal oxide sensors and catalytic reaction activities of catalyst. The concept of the surface unsaturated metal atoms serving as sensing reaction active sites not only deepens the understanding of the sensing reaction and catalytic reaction mechanism but also provides new insights into the design of advanced gas sensing materials, catalysts, and photoelectronic devices.