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Low-dimensional piezoelectric and quantum piezotronics are two important branches of low-dimensional materials, playing a significant role in the advancement of low-dimensional devices, circuits, and systems. Here, we firstly propose a solid-phase sintering and vapor-liquid-solid growth (SS-VLS-like) method of preparing a quantum-sized oxide material, i.e., black phosphorus (BP)@MgO quantum dot (QD) crystal with a strong piezoelectric response. Quantum-sized MgO was obtained by Mg slowly released from MgB2 within the confinement of a nanoflake BP matrix. Since the slow release of Mg only grows nanometer-sized MgO to hinder the further growth of MgO, we added a heterostructure matrix constraint: nanoflake BP. With the BP as the matrix confinement, MgO QDs embedded in the BP@MgO QD crystals were formed. These crystals have a layered two-dimensional (2D) structure with a thickness of 11 nm and are stable in the air. In addition, piezoresponse force microscopy (PFM) images show that they have extremely strong polarity. The strong polarity can also be proved by polarization reversal and a simple pressure sensor.

A series of novel phenomena such as optical nonlinear enhancement effect, transmission enhancement, orientation effect, high sensitivity to refractive index, negative refraction and dynamic regulation of low threshold can be generated by the control of surface plasmon (SP) with metal micro-nano structure and metal/material composite structure. The application of SP in nano-photonics, super-resolution imaging, energy, sensor detection, life science, and other fields shows an important prospect. Silver nanoparticles are one of the commonly used metal materials for SP because of their high sensitivity to refractive index change, convenient synthesis, and high controllable degree of shape and size. In this review, the basic concept, fabrication, and applications of silver-based surface plasmon sensors are summarized.

Silver nanowires (AgNWs), as conductive materials for flexible stretchable electrodes, do not only have high conductivity but also have a high specific surface area, excellent stretchability, and mechanical stability, showing great potential applications in flexible electronics such as foldable, stretchable electrodes and wearable devices, etc. This work successfully synthesized AgNWs with controllable morphology by an improved dual-alcohol process. The diameter, length, and size uniformity of AgNWs were effectively regulated by studying the reaction temperature, different control agents, and the dropping rate of the AgNO3 solution. The flexible stretchable electrodes were prepared using PDMS, paper, and nonwoven fabrics as substrate materials, and the impregnation method prepared the flexible stretchable electrodes of conductive fabrics. The properties of flexible stretchable electrodes of AgNWs based on different substrates were compared.

With paramount electrical, optical, catalytic, and other physical and chemical properties, van der Waals heterostructures (vdWHs) have captured increasing attention. vdWHs are two-dimension (2D) heterostructures formed via van der Waals (vdW) force, paving the way for fabricating, understanding, and applications of 2D materials. vdWHs materials of large lattice constant difference can be fabricated together, forming a series of unique 2D materials that cannot form heterostructures earlier. Additionally, vdWHs provide a new platform to study the interlayer interactions between materials, unraveling new physics in the system. Notably, vdWHs embody short-range bonds weaker than covalent and ionic bonds, almost only interactions between nearest particles are considered. Owing to a clear interface, vdW interaction between two different components, devices made by vdWHs can bring amazing physicochemical properties, such as unconventional superconductivity, super capacitance in intercalation 2D structure, etc. Recently, impressive progress has been achieved in the controlled preparation of vdWHs and various applications, which will be summarized in this review. The preparation methods comprise mechanical exfoliation, liquid phase stripping, physical vapor deposition, chemical vapor deposition, and metalorganic chemical vapor deposition. The applications sections will focus on photoelectric devices, logic devices, flexible devices, and piezotronics. Finally, some perspectives in the future on the controlled preparation of vdWHs with desired properties for advanced applications will be discussed.

All-solid-state batteries have been expected to overcome the safety problem of present lithium-ion batteries including organic liquid electrolytes. The materials with high ionic conductivity are urgently needed. In this paper, we reported a new ionic crystal Sr2Fe8O18 which can be applicated on solid electrolyte. Sr2Fe8O18 is a typical p-type semiconductor and shows a layered monoclinic crystal structure. The resistivities of Sr2Fe8O18 in the temperature range of 20 ~ 145 °C were above 107 Ω•cm. The microstructure of Sr2Fe8O18 was flaky, and the size of flaks were 1 µm ~ 5 µm. The E- P curve suggested that it was a ferroelectric semiconductor and had small ferroelectric effect. The dielectric response study (Cole-Cole plot) showed that Sr2Fe8O18 had two separated relaxation time, each of which contained a group of relaxation. The ionic conductivity σ of the sample was calculated to be 0.2196 × 10− 4 S/cm. The conductive mechanism which confirmed by the results of First principle calculation at 300K is mainly sublattice vacancy cation diffusion with self-diffusion coefficient D of 1.794 × 10− 5cm2/s. Fe ion has two dimensional diffusion path (x and y axial), and Sr ion has on dimensional diffusion path (x axial). The crystal structure of Sr2Fe8O18 shows tremendous potential application on the solid electrolyte preparation.

The weldability is essential for the practical applications of conductive adhesion. In this paper we focused on the weldability through microstructure, bonding strength, and shear strength of welding spot with co-doping of metal material Al and oxide material ZnO. When Al and ZnO doped separately, it can be seen from the results that Al-doping would increase the volume resistivity and adhesion strength for welding spot, and a proper amount of ZnO-doping would decrease the volume resistivity and improve adhesion strength for welding spot. Co-doping with Al and ZnO could decrease volume resistivity and enhance adhesion strength of welding spot concurrently, and the typical properties were 1.119 × 10−4 Ω cm for volume resistivity, 34.84 MPa for shear strength, and 17.00 MPa for bonding strength with addition of 4 wt% Al and 7 wt% ZnO.

Although most microwave absorbing materials (MAMs) have good absorption ability above 8 GHz, they perform poorly in the low-frequency range (1–8 GHz). Metal–organic frameworks (MOFs) derived carbon-based composites have been highly sought after in electromagnetic materials and functional devices, due to their high specific area, high porosity, high thermal stability, low reflection loss, and adjustable composition. In this review, we first introduce the three loss types of MAMs and argue that composite materials are effective ways to achieve broadband absorption. Secondly, the absorbing properties of traditional materials and MOF materials in the literature are compared, followed by a discussion of the promising strategies for designing MAMs with broadband absorption in low frequencies based on the recent progress. Finally, the main problems, fabrication methods, and applications are discussed for their future prospects.

The application of flexible electronics in the field of communication has made the transition from rigid physical form to flexible physical form. Flexible electrode technology is the key to the wide application of flexible electronics. However, flexible electrodes will break when large deformation occurs, failing flexible electronics. It restricts the further development of flexible electronic technology. Flexible stretchable electrodes are a hot research topic to solve the problem that flexible electrodes cannot withstand large deformation. Flexible stretchable electrode materials have excellent electrical conductivity, while retaining excellent mechanical properties in case of large deformation. This paper summarizes the research results of flexible stretchable electrodes from three aspects: material, process, and structure, as well as the prospects for future development.

The phase behaviors of an ABA star polymer and nanoparticles confined in a sphere with soft inner surface, which is grafted with homopolymer brushes have been studied by the self-consistent field theory (SCFT). The morphologies of mixture in the center slice of sphere were focused. Two cases are considered: one is that the nanoparticles interact with the B blocks and the other is that the nanoparticles preferentially wet the B blocks. Under the two conditions, through changing the block ratio of the ABA star polymer, the concentration and radius of the nanoparticles, the phase behaviors of the mixtures confined the soft sphere are studied systematically. With increasing the concentration of nanoparticles, the entropy and the steric repulsive interaction of nanoparticles, and the nanoparticle density distributions along the perpendicular line through the center of sphere are plotted. The phase diagram is also constructed to analyze the effects of the nanoparticle volume fraction and radius on morphologies of ABA star polymers, and to study the effect of confinement on the phase behaviors. The results in this work provide a useful reference for controlling the ordered structures in experiment, which is an effective way to fabricate the newly multifunctional materials.

1-1-3 Piezoelectric composites made of piezoelectric ceramic, epoxy resin and silicone rubber were prepared by using the modified 'slice and fill' technique. The effect of the volume percentage of ...

Micropower energy harvesting is one of key technologies for the micromation and practical development of wireless sensor and communication node networks. A self-adaptive piezoelectric vibration system based on modified homogeneous strain asymmetric PZT piezoelectric ceramic cantilever beam for the micropower energy harvesting was designed and prepared. A vertical cantilever was designed at the first time to obtain the homogeneous state of stress which can largely increase the power output and energy harvesting efficiency of piezoelectric cantilevers. In order to achieve the self-adaptive vibration, the asymmetric structure was adopted. Asymmetric cantilevers moved horizontally and changed the length of main cantilevers when affected by the variation in external frequency excitation, thus, the switching of resonant frequency was archived automatically without dissipating additional energy.

Limited by the low thermal resistance of composite material, ultra-low temperature curable conductive silver adhesive with curing temperature less than 100 °C needed urgently for the surface conduction treatment of piezoelectric composite material. An ultra-low temperature curable nano-silver conductive adhesive with high adhesion strength for the applications of piezoelectric composite material was investigated. The crystal structure of cured adhesive, SEM/EDS analysis, thermal analysis, adhesive properties and conductive properties of different content of nano-silver filler or micron-silver doping samples were studied. The results show that with 60 wt.% nano-silver filler the ultra-low temperature curable conductive silver adhesive had the relatively good conductivity as volume resistivity of 2.37 × 10−4 Ω cm, and good adhesion strength of 5.13 MPa. Minor micron-doping (below 15 wt.%) could improve conductivity, but would decrease other properties. The ultra-low temperature curable nano-silver conductive adhesive could successfully applied to piezoelectric composite material.

1-1-3 piezoelectric composites consisting of a PZT-5H ceramic, an epoxy resin matrix and a silicone rubber filler were prepared using a modified 'slice and fill' method. The effect of the ceramic volume percentage on the properties of the composite was analyzed both through experiments and simulations. By adopting the 1-1-3 structure, the electromechanical coupling coefficient of the piezoelectric composites could be increased to 0.69, and the acoustic impedance reduced to 6.81. The experimental results further showed that the variation of the ceramic volume percentage had no effect on the electromechanical coupling coefficient of the composites, but only affected the acoustic impedance. The presented piezoelectric composites can be used to design high-performance transducer.

The current ceramic/618 epoxy resin piezoelectric composite material is easily deformed due to temperature, which affects the performance of the transducer to send and receive signals. Therefore, finding piezoelectric composite materials with higher temperature stability has become an urgent task. In this paper, the temperature stability of two piezoelectric composite materials of ceramic/ 618 epoxy resin and ceramic/9110 W silicone resin in the range of 25 °C ~ 120 °C was investigated via the fiber Bragg grating method. The results show that, during 25 °C to 120 °C, the ceramic/9110 W silicone resin piezoelectric composite has obvious less deformation and more stable electromechanical properties than the ceramic/ 618 epoxy resin piezoelectric composite; its increase rate of deformation in three directions of length, width and thickness are 8.269 × 10−5 mm/°C, 6.728 × 10−6 mm/°C, and 8.476 × 10−6 mm/°C respectively; its resonant frequency, relative rate of change of frequency constant, quasi-static capacitance, relative dielectric constant and conductance increase with increasing temperature, and the maximum values are 289 kHz, 0.1529%, 1.67 nF, 1083.225 and 11.300 ms, respectively; its electromechanical coupling coefficient changes little with increasing temperature, the maximum and minimum values are 0.63 and 0.60, respectively. The ceramic/9110 W silicone resin piezoelectric composite can better ensure the stability of the transducer performance.

Searching low sintering temperature material with ultra-high Curie temperature (>800 °C) is urgent to seafloor hydrothermal vents detection. Bi 2 WO 6 was first improved to possess ultra-high Curie temperature and ultra-high depolarization temperature by experiment. The MnCO 3 was selected as dopant materials due to its excellent effect on improvement of sintering abilities and piezoelectric properties. The density test shows that Mn addition can obviously improve the density of Bi 2 WO 6 ceramics from 93.6% to 97.76%, and the grains also changed from round to layered. The crystal structure change with Mn addition was tested by synchrotron radiation and calculated by ab initio and Rietveld refinement. The symmetry group of ultra-high Curie temperature Bi 2 WO 6 is Aba2 (41). The XAFS results show that Mn atom more likely at the Bi-site in the crystal structure of Bi 2 W 1-x Mn x O 6 and the Mn ion has the valence alternation. The Curie temperature of Bi 2 W 1-x Mn x O 6 with increasing x are 997 °C, 915 °C, 890 °C, 729 °C, respectively, and the depolarization temperatures are around 940 °C, 895 °C, 825 °C, and 700 °C, respectively. The results show that Bi 2 W 1-x Mn x O 6 (x ≤ 0.01) ceramics are suitable for the ultra-high temperature applications of sensors or transducers on seafloor hydrothermal vents detection.

PZT, BSPT, PT, and two lead-free Bi 2 WO 6 , as five of the most representative piezoelectric systems with different Curie points were selected to study the origin of thermal depolarization in piezoelectric ceramics. The temperature dependences of dielectric loss and dielectric constant curves show that dielectric loss peaks of PZT MN , BSPT PNW , PT BFM , BW Li , and BW La are at 330 °C, 392.2 °C, 495 °C, 598.8 °C, and 781 °C, respectively. The results of thermal depoling measurement show that the depolarization temperature is closely related to the dielectric loss peak. And the peak points of dielectric loss curves below or at the Curie temperature are the points of complete depolarization.

The materials with high ionic conductivity are urgently needed for all-solid-state batteries. We reported a new ionic compound Sr2Fe8O18 which can be applicated on solid electrolyte. Sr2Fe8O18 is a typical p-type semiconductor and shows a layered monoclinic crystal structure. The ionic conductivity σ of the sample was calculated to be 0.2196×10-4 S/cm. The conductive mechanism which confirmed by the First principle calculation is mainly sublattice vacancy cation diffusion with self-diffusion coefficient D of 1.794×10-5cm2/s. Fe ion has two dimensional diffusion path and Sr ion has on dimensional diffusion path. Sr2Fe8O18 shows tremendous potential application on the solid electrolyte preparation.

Good conductive treatment of curved-surface piezoelectric composites could prevent failure of curved transducers, which are the core devices of many wideband and high-frequency sonar systems. A series of ratio between epoxy resin and curing agent were tested to investigate conductive treatments of curved-surface piezoelectric composites. The curved-surface piezoelectric composite was first prepared. The sample whose epoxy resin to and curing agent ratio was 100:150 showed the largest welding spot strength in many areas, but its homogeneity was not as good as samples with epoxy resin to curing agent ratio of 100:100 or 100:200. With increases in curing agent, the volume resistivities decreased, and the homogeneity became better.

Phase transition and thermal depolarization of PbTiO3 piezoelectric ceramics with Double Perovskite modified were investigated. With 5 mol% Double Perovskite (BFM, BNM, YNM, SNM), the PbTiO3 has a possibility to change the crystal structure to a large extent, and the sintering temperature can be controlled below 960 °C. With increasing ionic radius difference between addition and PbTiO3, the crystal structure of modified PbTiO3, measured by synchrotron radiation changed from Tetragonal (P4 mm) to Orthorhombic (Pmm2) and became more ordered (from 2 × 2 × 1 super cell to 6 × 2 × 2 super cell). The ordered Orthorhombic structure PT has higher phase transition temperature (496–540 °C) than the Tetragonal PT (481 °C). All modified PbTiO3 ceramics show high depolarization temperature. The depolarization temperatures of PT-BFM, PT-BNM, PT-YNM, and PT-SNM are 470 °C, 480 °C, 495 °C, and 505 °C, respectively.

The deformation of piezoelectric composite has many deadly effects on the transducers and the sonar systems, but the relative testing method never been focused. Here we developed a novel fiber-grating-sensing method for the study of temperature deformation of the piezoelectric composites for the first time. With the increase of temperature, the deformations of the piezoelectric composite in three dimensions increased, and the increasing speeds (all speeds means slop of fitted line) were 1.4 × 10−3 (length), 1.8833 × 10−4 (width) and 3.1439 × 10−5 (thickness), respectively. After adding the deform information the data for the frequency constant and dielectric constant were revised. The decreasing speed of frequency constant lowered from −2.0373 to −2.0263. The increasing speed of dielectric constant lowered from 2.6779 to 2.6580 in the range of 25 °C–75 °C, and from 1.9647 to 1.9559 in the range of 75 °C–125 °C.

The phase structure and electrical properties of BiYbO3–Pb(Zr,Ti)O3+x(mol%)Fe2O3 (BY–PZT–xFe) piezoelectric ceramics for applications at higher temperatures than those of PZT were investigated with a special emphasis on the influence of Fe2O3 content. All ceramics have a perovskite main phase with a tetragonal symmetry. The partial substitution of Fe3+ with Zr4+ and Ti4+ in the B-site caused a shrinkage of the perovskite lattice and a decreased tetragonality (c/a) with increasing x up to the solid solubility saturation at x=0.4. A lower tetragonality c/a, better grain morphology, and higher density as well as limited impurity phase were achieved at x=0.4 composition, all of which contribute to improved piezoelectric properties. The BY–PZT–xFe ceramics showed a high Curie temperature Tc up to 390 °C and good piezoelectric properties with d33 reaching 175 pC/N at x=0.4.

Two new high Curie temperature piezoelectric ceramics were reported for the first time. The PbTiNb2O8 and PbZrNb2O8 samples show single phase with space group of Am m 2 and C2 2 2, respectively. With the sintering temperature of 1120 °C and 970 °C, PbTiNb2O8 ceramics and PbZrNb2O8 ceramics have the highest Tc of 700.1 °C and 559.6 °C, respectively. The thermal depoling effects study shows that the depoling temperature of PbTiNb2O8 and PbZrNb2O8 ceramics is around 560 °C and 480 °C, respectively. The typical piezoelectric properties of PbTiNb2O8 and PbZrNb2O8 ceramics are: d33=16 pC/N, kp=0.11, Qm=102 and d33=20 pC/N, kp=0.16, Qm=42, respectively. All PbTiNb2O8 and PbZrNb2O8 samples are have low dielectric loss with ~10−4, which is good for the application of devices.

BaCu(B2O5) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO3 ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu2+ and Ba2+, while further increase was owing to the increase of dissolved Ba2+ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO3 ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm3 and energy efficiency of 98.83%.

Single phase of MgTiO 3 and (Mg 0.97 M 0.03 )TiO 3 (M = Ni, Zn, Co and Mn) ceramics was synthesized at the sintering temperature of 1275 °C. Relationships between structure and microwave dielectric properties were investigated on the basis of Rietveld refinement. The dielectric constant ( e r ) was affected by the relative density and the dielectric polarizability. The quality factor (Qf) increased with the increase of the packing fraction. The temperature coefficient of resonant frequency ( τ f ) moved toward positive due to the increase of A-site bond valence.

The phase constitution and phase structure of Zn 0.5 Ti 1− x Zr x NbO 4 ceramics were analyzed by multiphase structure refinement. The diffraction patterns of Zn 0.5 Ti 1− x Zr x NbO 4 showed that the ixiolite phase ZnTiNb 2 O 8 and rutile phase Zn 0.15 Nb 0.30 Ti 0.55 O 2 were obtained. The distortion of oxygen octahedron, bond valence of Ti-site and volume of oxygen octahedron were calculated. For the main phase ZnTiNb 2 O 8 , with substitution of Zr 4+ for Ti 4+ , the distortion of oxygen octahedron and the bond valence of Ti-site increased. The increase of Ti-site bond valence led to a harder rattling of Ti cations of the specimens. As a result, the contribution of the rattling effect to the polarizabilities of the specimens decreased, and subsequently the dielectric constant decreased. With increasing fraction of Zn 0.15 Nb 0.30 Ti 0.55 O 2 , the Qf value decreased. The decrease of τ f was mainly attributed to the increase of Ti-site bond valence. With the Ti-site bond valence increasing, the bonding strength between oxygen ion and Ti 4+ ion became stronger, and the dilution of the average ionic polarizability decreased.

Composite dielectrics, (1 − y )(Mg 1− x Zn x ) 1.8 Ti 1.1 O 4 – y CaTiO 3 , were prepared by the conventional solid-state route. The results of the X-ray diffraction and field emission scanning electron microscopy (FESEM) indicated the formation of solid solutions. Microwave dielectric properties of the composites were investigated systematically. For (Mg 1− x Zn x ) 1.8 Ti 1.1 O 4 system, superior dielectric properties ( ɛ r = 15.03, Q × f = 185,000 GHz, τ f = −45.1 × 10 −6 /°C) were achieved with (Mg 0.95 Zn 0.05 ) 1.8 Ti 1.1 O 4 sintered at 1375 °C. CaTiO 3 , as a τ f compensator, was added to form a temperature-stable ceramic system. For (1 − y )(Mg 0.95 Zn 0.05 ) 1.8 Ti 1.1 O 4 – y CaTiO 3 system, 0.93(Mg 0.95 Zn 0.05 ) 1.8 Ti 1.1 O 4 –0.07CaTiO 3 ceramic sintered at 1375 °C had optimal dielectric properties ( ɛ r = 18.26, Q × f = 96,000 GHz, τ f = −4.6 × 10 −6 /°C) which satisfied microwave applications in resonators, filters and antenna substrates.

The crystal structure and microwave dielectric properties of Zn 0.9 Ti 0.8− x Sn x Nb 2.2 O 8 ( x = 0.00, 0.05, 0.10, 0.15) ceramics sintered at temperatures ranging from 1100 °C to 1140 °C for 6 h were investigated. A single phase with ixiolite structure was obtained. With the increase of Sn content, the dielectric constant decreased attributed to the decrease of dielectric polarizability. The Qf value decreased with the decrease of packing fraction and grain size. The temperature coefficient of resonant frequency ( τ f ) increased due to the increase of the bond valence of Zn 0.9 Ti 0.8− x Sn x Nb 2.2 O 8 ceramics. The excellent microwave dielectric properties of ɛ = 35.05, Qf = 49,100 GHz, τ f = −27.6 × 10 −6 /°C were obtained for Zn 0.9 Ti 0.8− x Sn x Nb 2.2 O 8 ( x = 0.05) specimens sintered at 1120 °C for 6 h.

(Mg 1− x Co x )TiO 3 ( x = 0.00–0.09) ceramics were prepared by reaction sintering method. The correlations of crystal structure and the properties were analyzed on the basis of Rietveld refinement for specimens with different x . For x ≤ 0.5, solid solution phases with the ilmenite structure were obtained, which can be confirmed by the X-ray diffraction patterns and the lattice parameters measured. Whereas for x > 0.05, secondary phase was detected besides the main phase. Dielectric properties were closely related with theoretical dielectric polarizabilities, packing fraction and average octahedral distortion. By increasing x from 0.00 to 0.09, the Q × f value of the specimen decreased from a maximum of 289,400 GHz to 228,100 GHz. A fine combination of microwave dielectric properties ( ɛ r ∼ 16.1, Q × f ∼ 289,400 GHz, τ f ∼ −54.4 × 10 −6 /°C) was achieved for MgTiO 3 ceramics sintered at 1350 °C for 4 h.

Doping behaviors of NiO and Nb2O5 in BaTiO3 in two doping ways and dielectric properties of BaTiO3-based X7R ceramics were investigated. When doped in composite form, the additions rendered higher solubility than that doped separately due to the identical valence between the complex (Ni1/32+Nb2/35+)4+ and Ti4+. NiO–Nb2O5 composite oxide was more effective in broadening dielectric constant peaks which was responsible for the temperature-stability of BaTiO3 ceramics. A reduction in grain size was observed in the specimens with 0.5–0.8 mol% NiO–Nb2O5 composite oxide, whereas the abnormal growth of individual grains took place in the 1.0 mol% NiO–Nb2O5 composite oxide-doped specimen. When the specimen of BaTiO3 doped with 0.8 mol% NiO–Nb2O5 composite oxide was sintered at 1300 °C for 1.5 h in air, good dielectric properties were obtained and the requirement of (EIA) X7R specification with a dielectric constant of 4706 and dielectric loss lower than 1.5% were satisfied.

High quality factor and near-zero temperature coefficient of resonant frequency (τf) are the two key issues for a certain microwave dielectric material system used in microstrip patch antennas. ZnTiO3-based ceramics is a promising candidate for microstrip patch antennas. On inhibiting the decomposition of ZnTiO3 by adding sufficient amount of MgO, high quality factor microwave dielectric material (Zn0.7Mg0.3)TiO3 was obtained. The deviations between theoretical and observed dielectric polarizabilites, the packing fraction, and bond valence were calculated to analyze correlation between structure and properties of (Zn0.7Mg0.3)TiO3. TiO2 was added to adjust τf of (Zn0.7Mg0.3)TiO3, and 0.82(Zn0.7Mg0.3)TiO3–0.18TiO2 with an er of 28.5, a Qf of 125,050 GHz, and a near-zero τf which satisfied the requirement as a substrate material for microstrip patch antenna was obtained at 1100 °C. In addition, a dielectric microstrip antenna was designed and fabricated using the proposed dielectric materials. The microstrip patch antenna exhibited a −34.96 dB return loss and a 1.05 voltage standing wave ratio at 2.5 GHz.

A new low-loss, low-temperature sinterable microwave dielectric material ZnTiNbTaO8 was investigated for the first time. Single phase ZnTiNbTaO8 was obtained by the conventional solid-state route and sintered at 1120°C–1200°C for 6 h. Theoretical density, packing fraction, bond valence, and oxygen octahedron distortion were calculated. The excellent microwave dielectric properties of e = 36.3, Qf = 67 000 GHz, τf =−57.66 × 10−6/°C were obtained from the new ZnTiNbTaO8 materials sintered at 1140°C for 6 h.

Microwave dielectric properties and microstructures of (Mg0.95Co0.05)TiO3 ceramics prepared by a new sintering method (reaction-sintering method) were investigated. A pure phase of (Mg0.95Co0.05)TiO3 was obtained by the new method and excellent dielectric properties were observed due to uniformities of the microstructure and the phase. In contrast, the secondary phase (Mg0.95Co0.05)Ti2O5 was observed in samples prepared by conventional sintering method. In order to study the influence of secondary phase on the microwave dielectric properties quantitatively, the weight fraction of (Mg0.95Co0.05)Ti2O5 was calculated on the basis of Rietveld refinement. The pore-freeɛr values of specimens prepared by two different methods indicated that porosity plays an important role in the ɛr values of (Mg0.95Co0.05)TiO3 ceramics. Specimens sintered by reaction-sintering method at 1350 °C for 4 h possess excellent dielectric properties with an ɛr of 16.3, a Q × f value of 244,500 GHz, and a τf value of −53.5 ppm/°C.

The crystal structure and microwave dielectric properties of ZnTi(Nb 1− x Ta x ) 2 O 8 ceramics were investigated. The ZnTi(Nb 1− x Ta x ) 2 O 8 ceramics mainly contained ixiolite structure phase ZnTiNb 2 O 8 and an unknown Columbite-type phase. The change of microwave dielectric properties was affected by the change of crystal structure of each phase. In ZnTi(Nb 1− x Ta x ) 2 O 8 ceramics, the Columbite structure phase with increasing degree of ordering led to decrease of dielectric constant, increase of Qf , and to τ f moving in the positive direction. The ZnTiNb 2 O 8 with decreasing cation valence led to the increase of τ f . The typical values were: e = 34.05, Qf = 40,000 GHz, τ f = −66.07 ppm/°C.

Microwave dielectric ceramics of Mg4Nb2O9 were prepared by the sol–gel method and their microwave dielectric properties and microstructure were investigated in this study. Firstly, highly reactive nanosized magnesium niobate powders were successfully synthesized at 550 °C in oxygen atmosphere with particle size of 30–40 nm. And the phase formation was investigated by means of DTA–TG and XRD analyses. Subsequently, the sintering ability and microwave dielectric properties of Mg4Nb2O9 ceramics were studied under various sintering temperatures ranging from 1150 °C to 1325 °C. As the sintering temperature increased from 1150 °C to 1325 °C, the density values, the ɛr values and the Qf values increased and saturated at 1250 °C, whereas the Qf values decreased at the sintering temperature above 1300 °C .The τf values were ranged from −48.7 to −37.8 ppm/°C. Due to the increased density and appropriate grain growth the Mg4Nb2O9 ceramics sintered at 1250 °C had the excellent microwave dielectric properties of ɛr = 12.3, Qf = 165,000 GHz and τf = −47.5 ppm/°C. The results showed that the sintering temperature was significantly reduced by the sol–gel process.

The correlation of crystal structure and microwave dielectric properties for Zn(Ti 1− x Sn x )Nb 2 O 8 ceramics were investigated. The Zn(Ti 1− x Sn x )Nb 2 O 8 ceramics contained ZnTiNb 2 O 8 and an unknown Columbite-type phase. The columbite structure phase with increasing degree of ordering led to decrease of dielectric constant, increase of Qf and τ f . The ZnTiNb 2 O 8 with decreasing cation valence led to increase of τ f . The typical values were: ɛ = 30.88, Qf = 43,500 GHz, τ f = −54.32 × 10 −6 / °C.

(Mg 1 − x Cox)TiO 3 (x = 0, 0.03, 0.05, 0.1, 0.2) were synthesized by the solid-state reaction method. The effect of Co 2 O 3 additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO 3 ceramics was investigated. The microwave dielectric properties of the (Mg 1 − x Co x)TiO 3 ceramics system were found to vary with amount of Co 2 O 3 additive and sintering temperature which were attributed to the variation of second phase and densification of the ceramics. By properly adjusting the amount of Co 2 O 3 , a small dielectric loss of 0.2 × 10−4 was obtained for (Mg 1 − x Co x )TiO 3 ceramics.

The microwave dielectric properties and crystal structure of the ZnO-xSnO 2 -(2–x)TiO 2 -Nb 2 O 5 ceramics were investigated. There were two phases existing in the ceramics: ixiolite phase ZnTiNb 2 O 8 and rutile phase Zn 0.15 Nb 0.30 Ti 0.55 O 2 . The mass percentage of phase ZnTiNb 2 O 8 increased with increasing of SnO 2 content from 0.02 to 0.08, and when x ≥ 0.08 the mass percentage of phase ZnTiNb 2 O 8 decreased. For the dielectric constant and dielectric loss of the ceramics, these values ranged from 49 to 63 and from 2.4× 10− 4 to 0.30× 10− 4, respectively. The temperature coefficient of the ceramics decreased from −132 × 10− 6/°C to −12 × 10− 6/°C.

Ag(Nb0.6Ta0.4)O3 (ANT) ceramics were synthesized by conventional solid-state method and wet chemical method (sol–gel method). The effects of preparation methods on synthesis temperature, phase structure, morphology, Raman spectra, and dielectric properties of ANT ceramics were investigated. For sol–gel method, K2CO3 was used to dissolve Nb2O5 and Ta2O5, avoiding use of strong corrosive hydrofluoric acid. The results showed that the synthesis temperature of ANT phase obtained by sol–gel method was 700 °C, while that by solid-state method was 950 °C. The nanopowders around 40 nm were obtained by sol–gel method, while the micro-powders around 1.5 μm by solid-state method. In addition, the decrease of vibration frequency of A1g(O) stretch mode indicated that the Nb–O or Ta–O bonds became weak, which lead to high permittivity. The dielectric properties of the ceramics prepared by the two methods were different. Notably, the dielectric loss (6.6 × 10−4) of ANT ceramic synthesized by sol–gel method was much lower than that (22.8 × 10−4) by solid-state method.

The microstructure and electrical properties of a new ternary high temperature piezoelectric ceramic system (1−x)(0.1BiYbO3–0.9PbTiO3)–xPb(Zn1/3Nb2/3)O3 (BYPT–PZN, x=0.05–0.5) were reported. The ternary system had a perovskite main phase with a tetragonal symmetry. With increasing PZN content, the tetragonality decreased, and interestingly, both the piezoelectric properties and mechanical quality factor of the samples were largely improved. Microstructural characteristics indicated that the improved piezoelectric performance was also due to the improved density, structural stability and homogeneity. The sample with 40 mol% of PZN (x=0.4) showed the optimum piezoelectric response and a Tc of around 400 °C. However, direct high temperature d33 measurement via the Berlincourt method indicated that depolarization in the sample did not occur up to 350 °C.

The ultra-low temperature curable conductive silver adhesive needed urgently for the surface conductive treatment of piezoelectric composite material. The effect of diluent acetone on ultra-low temperature curable conductive silver adhesive were investigated for surface conductive treatment of piezoelectric composite material. In order to improve the operability and extend the life of the conductive adhesive, the diluent was added to dissolve and disperse conductive adhesive. With the increase of the content of diluent, the volume resistivity of conductive adhesive decreased at first and then increased, and the shear strength increased at first and then decreased. When the acetone content is 10%, the silver flaky bonded together, arranged the neatest, the smallest gap, the most closely connected, the surface can form a complete conductive network, and the volume resistivity is 2.37 × 10-4Ω cm, the shear strength is 5.13MPa.