Jing Yulan

The low-temperature sintering and microwave dielectric properties of (Zn0.7Mg0.3)TiO3 ceramics with H3BO3

The effects of the addition of H3BO3 on the microstructure, phase formation, and microwave dielectric properties of (Zn0.7Mg0.3)TiO3 ceramics sintered at temperatures ranging from 890 °C to 950 °C are investigated. H3BO3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 °C due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H3BO3. With the increase in H3BO3 content, the dielectric constant (er) monotonically increases, but the quality factor (Q × f) reaches a maximum at 1 wt% H3BO3, and the apparent density of ZMT ceramics with H3BO3 ≥ 1 wt% gradually decreases. At 950 °C, the ZMT ceramics with 1% H3BO3 exhibit excellent microwave dielectric properties: er = 19.8, and Q × f = 43800 GHz (8.94 GHz).

Effects of BaCu(B2O5) addition on sintering temperature and microwave dielectric properties of Ba5Nb4O15–BaWO4 ceramics

The effects of BaCu(B2O5) (BCB) addition on the microstructure, phase formation, and microwave dielectric properties of Ba5Nb4O15−BaWO4 ceramic are investigated. As a sintering aid, BaCu(B2O5) ceramic could effectively lower the sintering temperature of Ba5Nb4O15−BaWO4 ceramic from 1100 °C to 950 °C due to the liquid-phase effect. Meanwhile, BaCu(B2O5) addition effectively improves the densification of Ba5Nb4O15−BaWO4 ceramic and significantly influences the microwave dielectric properties. X-ray diffraction analysis reveals that Ba5Nb4O15 and BaWO4 coexist with no crystal phase of BaCu(B2O5) in the sintered ceramics. The Ba5Nb4O15−BaWO4 ceramics with 1.0 wt% BaCu(B2O5) sintered at 950 °C for 2 h presents good microwave dielectric properties of er = 19.0, high Q×f of 33802 GHz and low τf of 2.5 ppm/°C.

Strong and broadband terahertz absorber using SiO2-based metamaterial structure

We design and experimentally demonstrate a broadband metamaterial absorber in the terahertz (THz) band based on a periodic array of aluminum (Al) squares with two different sizes. A thin silicon dioxide (SiO2) film rather than a conventional polyimide (PI) layer is used as a dielectric spacer to separate Al squares from the platinum (Pt) ground plane in our design, which significantly improves the design precision and the feasibility of the device fabrication. The combination of different sizes of Al squares gives rise to an absorption bandwidth of over 210 GHz with an absorption of over 90%. Our results also show that our device is almost polarization-insensitive. It works very well for all azimuthal angles with an absorption of beyond 80%.

Influences of Bi2O3/V2O5 Additives on the Microstructure and Magnetic Properties of Lithium Ferrite

Lithium ferrite materials with different concentrations of Bi2O3 and V2O5 additives are prepared by the conventional ceramic technique. The x-ray diffraction analysis proves that the additives do not affect the final crystal phase of the lithium ferrite in our testing range. Both Bi2O3 and V2O5 additives could promote densification and lower sintering temperature of the lithium ferrite. The average grain size first increases, and then gradually decreases with the Bi2O3 content. The maximal grain size appears with 0.25 wt% Bi2O3. The average grain size first increases, and then is kept almost unchanged with the V2O5 content. The maximal average grain size of the samples with V2O5 additive is much smaller than that of the samples with Bi2O3 additive. Furthermore, the V2O5 additive more easily enters the crystal lattice of the lithium ferrite than the Bi2O3 additive. These characteristics evidently affect the magnetic properties, such as saturation flux density, ratio of remanence Br to saturation flux density Bs, and coercive force of the lithium ferrite. The mechanisms involved are discussed.

Large Magnetoresistance Based on Double Spin Filter Tunnel Barriers

We propose and theoretically analyse a double magnetic tunnel device that takes advantages of the spin filter effect. Two magnetic tunnel barriers are formed by different spin filters which have different barrier heights. The magnetoresistance of the device is low (high) when the magnetic moments of the two spin filters are parallel (antiparallel). We present a theoretical calculation of the magnetoresistance based on electric tunnel effect. In addition, the effect of the difference barrier heights and exchange splitting energies between the two spin filters are also analysed in detail. The numerical results show that the spin filter in this configuration gives a magnetoresistance larger than that with standard magnetic tunnel junctions.