Crystal Chemistry, Raman Spectra, and Bond Characteristics of Trirutile-Type Co0.5Ti0.5TaO4 Microwave Dielectric Ceramics.

A novel trirutile-type Co0.5Ti0.5TaO4 ceramic was reported here for the first time. The correlations between the sintering behavior, crystal structure, chemical bond, and dielectric properties were investigated. Pure Co0.5Ti0.5TaO4 ceramic was synthesized in the temperature range of 1000-1100 °C. A trirutile structure and refined parameters of a = b = 4.71163 Å, c = 9.13586 Å, and Vcell = 202.811 Å3 could be obtained (1075 °C). According to the P-V-L chemical bond theory, majority contributions to the dielectric constant originated from Ta-O bonds, owing to its largest bond ionicity and bond susceptibility values. The experimental dielectric constant is close to the theoretical values calculated via the P-V-L chemical bond theory and Clausius-Mossotti relationship. The Ta-O bonds that present the largest lattice energy are also the main factors influencing the intrinsic loss. The τf value is consistent with the oxygen distortions of the octahedron. More importantly, variations of the densification, average grain size, and grain boundary are crucial factors for development of the microwave dielectric properties. The Raman spectra and group theory were analyzed together, and the results indicated that the A1g mode at 687.45 cm-1, which reflects the stretching vibrations of the O anions, dominates the Raman vibrations. Typical microwave dielectric properties of Co0.5Ti0.5TaO4 ceramics were obtained when sintered at 1075 °C: εr = 40.69, Qf = 17291 GHz, and τf = 114.54 ppm/°C.

Structural Evolution and Microwave Dielectric Properties of xZn0.5Ti0.5NbO4-(1- x)Zn0.15Nb0.3Ti0.55O2 Ceramics.

Structure and microwave properties of xZn0.5Ti0.5NbO4-(1 - x)Zn0.15Nb0.3Ti0.55O2 ceramics in the range of x = 0.0-1.0 were investigated. Rietveld refinement analysis and Raman spectra show that rutile- and orthorhombic-type solid solutions formed at 0-0.2 and 0.65-1, a composite at 0.2-0.64. In the solid solution regions, chemical bonds are enlarged. In this case, the Zn/Ti/Nb-O1 bond covalency and bond susceptibility are reduced, and lattice energy and thermal expansion coefficient increase along with x increases, which is mainly responsible for the development of microwave dielectric properties. Furthermore, far-infrared spectra and a classical oscillator model were used to discuss the intrinsic dielectric properties in detail. Temperature stable ceramic was obtained for x = 0.516: εr ∼ 46.11, Q × f ∼ 27 031 GHz, and τf ∼ -1.51 ppm/°C, which is promising for microwave applications.

Achieving ultrahigh energy storage density and efficiency in 0.90NaNbO3-0.10BaTiO3 ceramics via a composition modification strategy.

Ceramic capacitors feature great power density, fast charge/discharge rates, and excellent thermal stability. The poor energy storage density of ceramic capacitors, on the other hand, significantly limits their application in power systems. In this work, a high recoverable energy storage density of Wrec = 2.68 J cm-3 and an ultrahigh efficiency of η = 90% are simultaneously achieved in the 0.90NaNbO3-0.10BaTiO3 ceramic by doping (Bi0.7La0.3)(Mg0.67Ta0.33)O3 (NNBT-xBLMT). Due to its high bandgap, the NNBT-0.10BLMT ceramic has a large dielectric breakdown strength (BDS) of 414 kV cm-1, consistent with the first-principles calculation based on density functional theory (DFT). Moreover, the NNBT-0.10BLMT ceramic exhibits excellent charge/discharge characteristics, with an ultrahigh current density CD of 526.06 A cm-2 and a high power density PD of 52.61 MW cm-3. In particular, the NNBT-0.10BLMT ceramic exhibits an outstanding temperature (20 °C-110 °C), frequency (10 Hz-120 Hz), and cycling (104 cycles) stability, highlighting its application potential in MLCCs.

Ferroelectric-Relaxor Crossover and Energy Storage Properties in Sr2NaNb5O15-Based Tungsten Bronze Ceramics.

Filled and unfilled Sr2NaNb5O15-based tungsten bronze ceramics based on Gd doping were prepared using a traditional solid-state reaction method. Relaxor behaviors of the two different systems were analyzed, and the corresponding energy storage performance was also characterized. With the support of weakly coupled polar nanoregions and a non-polar matrix, an energy storage density of 2.37 J/cm3 and an efficiency of 94.4% were obtained in the Sr1.82Gd0.12NaNb5O15 ceramic. A discharge energy density of 2.51 J/cm3 and a power density of 59.1 MW/cm3 further proved its prospect for practical applications. In addition, the thermal stability and fatigue resistance of the ceramic were also evaluated. At the same time, under the theoretical framework of a perovskite and tungsten bronze, the contribution of vacancies to the local structure and relaxor behavior was briefly discussed. Because the currently used ceramics do not contain easily reducible metal oxides, this work lays the foundation for the development of multilayer ceramic capacitors that use base metals as internal electrodes.

Significantly Enhanced Energy Storage Performance in High Hardness BKT-Based Ceramic via Defect Engineering and Relaxor Tuning.

Hybrid electric cars and pulsed power technologies have increased the demand for capacitors with high energy density, wide temperature stability, high operating voltage, and good mechanical qualities. In this work, (1 - x) (0.6Bi0.5K0.5TiO3-0.4BiFeO3)-x(Na0.4Sm0.2NbO3) ((1 - x) (BKTBF)-xNSN) relaxor ceramics were prepared by constructing morphotropic phase boundary (MPB) combined with oxygen vacancy defect engineering. It is worth noting that the 0.6BKT-0.4BFO ceramics at MPB have a high Pmax ∼ 60 µC/cm2. The ultra-hard (HV = 10.7 GPa) BKTBFO-0.16NSN relaxor ferroelectric ceramic achieves a high Wrec of 6.52 J/cm3, a working temperature of 20-120 °C, and a working frequency of 1-1000 Hz. Additionally, the BKTBFO-0.16NSN ceramic demonstrates comprehensive pulse charge-discharge performance (Imax = 17.2 A, CD = 546.7 A/cm2, PD = 54.7 MW/cm3, and t0.9 = 59 ns) and excellent stability (25-125 °C and 104 charge-discharge cycles). This study offers a novel approach for the practical implementation of high-performance pulse capacitors, which will undoubtedly stimulate further research and development of high-Pmax energy storage dielectrics (such as BNT, BKT, and BFO).

Photocatalytic activity of attapulgite-TiO2-Ag3PO4 ternary nanocomposite for degradation of Rhodamine B under simulated solar irradiation.

An excellent ternary composite photocatalyst consisting of silver orthophosphate (Ag3PO4), attapulgite (ATP), and TiO2 was synthesized, in which heterojunction was formed between dissimilar semiconductors to promote the separation of photo-generated charges. The ATP/TiO2/Ag3PO4 composite was characterized by SEM, XRD, and UV-vis diffuse reflectance spectroscopy. The co-deposition of Ag3PO4 and TiO2 nanoparticles onto the surface of ATP forms a lath-particle structure. Compared with composite photocatalysts consisting of two phases, ATP/TiO2/Ag3PO4 ternary composite exhibits greatly improved photocatalytic activity for degradation of rhodamine B under simulated solar irradiation. Such ternary composite not only improves the stability of Ag3PO4, but also lowers the cost by reducing application amount of Ag3PO4, which provides guidance for the design of Ag3PO4- and Ag-based composites for photocatalytic applications.

Influence of (Al1/3W2/3)5+ co-substitution for Nb5+ in NdNbO4 and the impact on the crystal structure and microwave dielectric properties.

NdNb1-x(Al1/3W2/3)xO4 (x = 0.03-0.07) solid solution compounds were synthesized and characterized via solid-state reaction. XRD patterns reveal the formation of a single fergusonite phase, and the dependence of microwave dielectric properties on its structural characteristic was investigated based on Rietveld refinements together with complex chemical bond theory. The variation of dielectric constant is attributed to the Nb/Al1/3W2/3-O bond ionicity. The grain size and total lattice energy are both associated with quality factor, and the temperature coefficient is affected by oxygen and bond valence of the Nb site. Infrared reflectivity spectrum analysis illustrated that the permittivity is primarily due to ion polarization in the microwave frequency region. Notably, the following properties of NdNb1-x(Al1/3W2/3)xO4 (x = 0.04) ceramics were obtained: εr ∼ 19.04, Q × f ∼ 58 219 GHz and τf ∼ -41.14 ppm/°C.

Improved Thermoelectric Performances of SrTiO3 Ceramic Doped with Nb by Surface Modification of Nanosized Titania.

Nb-doped SrTiO3 ceramics doped with the surface modification of nanosized titania was prepared via liquid phase deposition approach and subsequent sintered in an Ar atmosphere. The surface modification of nanosized titania significantly improved the ratio of the electrical conductivity to thermal conductivity of SrTiO3 ceramic doped with Nb, and has little impact on the Seebeck coefficient, thus obviously improving the dimensionless thermoelectric figure of merit (ZT value). The surface modification of nanosized titania is a much better method to lower the thermal conductivity and to enhance the electrical conductivity than the mechanical mixing process of nanosized titania. The highest ZT value of 0.33 at 900 K was obtained. The reason for the improved thermoelectric performances by the surface modification of nano-sized titania was preliminary investigated.

Simulations and analysis of a piezoelectric micropump.

A number of micropumps have been proposed in the last few years based on different actuating principles and fabricated by different technologies. However, many of those micropumps have been designed taking into account primarily available microfabrication technologies rather than appropriate pump performance analysis. In fact, not all papers are available in the literature presenting theoretical models usable to describe the functioning and predict the performance of those micropumps. In this paper, we present a new micropump model and FEA method suitable for guiding the design and predicting the performance of a micropump actuated by a piezoelectric actuator. The model takes into account the influence of piezoelectric transducer and pump geometry. Simulations have been performed and compared with results of experiments on a prototype micropump fabricated in our laboratory.