Small Dielectric Loss Research Articles

Dielectric and electromechanical properties of modified cement/polymer based 1–3 connectivity piezoelectric composites containing inorganic fillers

Abstract Here the modified cement/polymer based 1–3 piezoelectric composites containing inorganic fillers were prepared. The influences of filler content and composite thickness on dielectric and electromechanical properties of the composites were investigated. The results indicate that the composites with fillers of graphite and strontium ferrite (Sr-ferrite) have larger static relative dielectric constant and smaller dielectric loss than those with silicon powder. The strontium ferrite can improve the thickness electromechanical coupling property of the composites. When the strontium ferrite content is 5 wt.% of the cement/polymer matrix, the piezoelectric composite has the largest thickness electromechanical coupling coefficient of 64.27% and the smallest mechanical quality factor 8.64. The graphite filler shows a certain suppression effect on the planar resonance of the composites. The coupling effects between the planar and thickness modes of the composites were reduced by decreasing the composite thickness, and pure thickness mode resonance can be obtained at a small composite thickness.

Effect of Ba Substitution on Microstructure, Dielectric and Ferroelectric Properties of BiFeO3 Ceramics

Pure BiFeO3 (BFO) ceramics and Bi1-xBaxFeO3 (x=0.1, 0.15, 0.2, and 0.25) ceramics were prepared by sol-gel method. A structural transition from rhombohedral R3c to triangle R3m occurs in the Ba doped BFO ceramics. The Ba doped BFO ceramics exhibit larger dielectric constant, smaller dielectric loss, and better ferroelectric hysteresis loop, which could be attributed to the lower concentration of charge defects and the structural transition.

Reduced leakage current, enhanced ferroelectric and dielectric properties of (La, Fe)-codoped Bi0.5Na0.5TiO3-based thin films

The lead-free Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–SrTiO3 (BNT–BKT–ST) and (La, Fe)-codoped Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–SrTiO3 (BNT–BKT–ST–LaFe) thin films were deposited on Pt/Ti/SiO2/Si substrates by the sol–gel method. Both the BNT–BKT–ST and BNT–BKT–ST–LaFe thin films exhibit pseudo-cubic perovskite structure and uniform grain size. The leakage current density of BNT–BKT–ST–LaFe thin film at 400kV/cm is reduced by approximately two orders of magnitude compared with BNT–BKT–ST thin film. Enhanced ferroelectric property is achieved in BNT–BKT–ST–LaFe film with a large remanent polarization of 13μC/cm2. At the same time, the BNT–BKT–ST–LaFe film also exhibits a large dielectric constant of 420 and small dielectric loss of 0.055 at 100kHz. These results indicate that the (La, Fe)-codoped BNT–BKT–ST thin film is a promising candidate in lead-free ferroelectric materials.

Multiferroic and dielectric properties of Bi4LaTi3FeO15 ceramics

Single phase Bi4LaTi3FeO15 ceramics with a four-layered Aurivillius structure were synthesized by successfully inserting LaFeO3 into Bi4Ti3O12 matrix, and their structural, multiferroic and dielectric properties were investigated. Typical ferroelectric behavior with remnant polarization (2Pr) of about 12μC/cm2, large dielectric constant, small dielectric loss and a weak ferromagnetic behavior are obtained simultaneously at room temperature. As a result, possible magnetoelectric coupling effect is obtained near the ferromagnetic Curie temperature. Meanwhile, the weak ferromagnetism can be enhanced at lower temperature, and thus a larger saturation magnetization of about 1.2emu/g is obtained at 5K. In addition, two sets of dielectric relaxation are observed and discussed based on defect relaxation theory.

Effect of Mn Substitution on Microstructures, Dielectric and Magnetic Properties of BiFeO<sub>3</sub> Ceramics

Pure BiFeO3 ceramics and BiMnxFe1-xO3 (x=0.1, 0.15, 0.2, and 0.25) ceramics were prepared by sol-gel method. A structural phase transition from rhombohedral R3c to triangle R3m occurred in Mn-doped BFO ceramics. Mn-doped BFO ceramics exhibited better crystallinity, larger dielectric constant as well as smaller dielectric loss. Besides, a small nonlinearity of magnetization-field curves M(H) was observed, the remanent magnetization increased with the increase of manganese content, and all the BiMnxFe1-xO3 ceramics showed the typical antiferromagnetic, which could be attributed to the effective decrease in the concentration of oxygen vacancies, and the corresponding structural transition.

Effects of Ba and Ti Codoping on Stoichiometric and Nonstoichiometric BiFeO<sub>3</sub> Multiferroic Ceramics

Bi0.9Ba0.1Fe0.95O3 and Bi0.9Ba0.1FexTi0.05O3 (x=0.95, 0.925, 0.90) ceramics were prepared through conventional solid state reactions. X-ray diffraction analyses indicated that a high content of perovskite phase was obtained for all the four compositions. While the three (Ba,Ti)-codoped compositions all showed a higher resistivity than Bi0.9Ba0.1Fe0.95O3, and Bi0.9Ba0.1Fe0.925Ti0.05O3 had the best electrical and dielectric properties among the three (Ba,Ti)-codoped compositions, including the largest dielectric constant, the smallest dielectric loss at low frequency range, and the highest electrical resistivity. Magnetic hysteresis loop measurement revealed that the four compositions had similarly enhanced magnetic properties. It is concluded that much attention should be paid to fine composition adjustment when multiple elements are co-doped to BiFeO3 system.

A Novel Technique to Measure Small Dielectric Losses Using Cylindrical Cavity Resonator at X Band

A technique has been designed to determine the relative permittivity and dielectric loss of low loss materials using a cylindrical cavity resonator at X band. This technique has been tested over some standard materials with satisfactory results compared to some existing standard methods for measuring tanS. The measurements are performed TE111 mode with the aid of Agilent E4418B EPM series power meter and Agilent 53150A 20 GHz frequency counter.

Design, fabrication, and properties of 2-2 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution.

The laminated 2-2 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution were fabricated by employing Lead Zirconium Titanate ceramic as active phase, and mixture of cement powder, epoxy resin, and hardener as matrix phase with a mass proportion of 4:4:1. The dielectric, piezoelectric, and electromechanical coupling properties of the composites were studied. The composites with large total volume fraction of piezoelectric phase have large piezoelectric strain constant and relative permittivity, and the piezoelectric and dielectric properties of the composites are independent of the dimensional variations of the piezoelectric ceramic layer. The composites with small total volume fraction of piezoelectric phase have large piezoelectric voltage constant, but also large dielectric loss. The composite with gradually increased dimension of piezoelectric ceramic layer has the smallest dielectric loss, and that with the gradually increased dimension of matrix layer has the largest piezoelectric voltage constant. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with varied surface vibration amplitude of the transducer.

Bi2SiO5 Doping Concentration Effects on the Electrical Properties of SrBi2Ta2O9 Films

In this paper, we investigated the microstructure and electrical properties of Bi2SiO5 (BSO) doped SrBi2Ta2O9 (SBT) films deposited by chemical solution deposition. X-ray diffraction observation indicated that the crystalline structures of all the BSO-doped SBT films are nearly the same as those of a pure SBT film. Through BSO doping, the 2Pr and 2Ec values of SBT films were changed from 15.3 μC/cm2 and 138 kV/cm of pure SBT to 1.45 μC/cm2 and 74 kV/cm of 10 wt.% BSO-doped SBT. The dielectric constant at 1 MHz for SBT varied from 199 of pure SBT to 96 of 10 wt.% BSO-doped SBT. The doped SBT films exhibited higher leakage current than that of non-doped SBT films. Nevertheless, all the doped SBT films still had small dielectric loss and low leakage current. Our present work will provide useful insights into the BSO doping effects to the SBT films, and it will be helpful for the material design in the future nonvolatile ferroelectric memories.

Effect of Lithium Fluoride on the Dielectric Properties of Barium Titanate

The purpose of this study was to investigate the dielectric properties of BaTiO3 (BTO) ceramics sintered with the aid of lithium fluoride. BTO with various ratios BaO/TiO2 (0.97, 1.00, 1.03) was synthesized by calcination of BaCO3 and TiO2 at 1100 °C. The different BTO powders were mixed with 1, 2 or 3 wt.% of LiF and then wet-ground in ethanol. The mixtures were cold-pressed to pellets with “latex” as a binder. The disks were sintered in free-air or sealed tube at 750, 850, 950 or 1100 °C, respectively, for 2 or 8 h. The obtained ceramics were checked by X-ray diffraction, scanning electron microscopy, differential thermal analyses and Auger microprobe. Dielectric measurements were carried out under vacuum at 1 kHz in the temperature range 180–500 K. Chemical analyses were performed and lithium and fluorine losses were calculated. Results show that the addition of LiF to BTO lowered both the sintering temperature and the ferroelectric Curie temperature T C. Most ceramics exhibited a broad maximum of the permittivity $${\varepsilon_{\rm r}^{\prime}}$$ and small dielectric losses tan $${\delta}$$ at T C. The best dielectric characteristics were observed from BTO (1.03) ceramic sintered with 2 wt.% of LiF at 950 °C for 2 h and then reheated at 1200 °C for 2 h in sealed tube: T C = 248 K, $${\varepsilon_{\rm r}^{\prime}}$$ at T C = 8650, tan $${\delta}$$ at T C = 6 × 10−3. The majority of prepared ceramics could be of interest in the manufacture of Z5U multilayer capacitors at low factory cost.

Effect of Eu–Ni substitution on electrical and dielectric properties of Co–Sr–Y-type hexagonal ferrite

Single phase nanostructured Eu–Ni substituted Y-type hexaferrites with nominal composition Sr2Co2−xNix EuyFe12−yO22 (x=0.0–1, y=0.0–0.1) were synthesized by the normal microemulsion method. X-ray diffraction (XRD) technique was employed for phase analysis and indexing of each pattern corroborates that well defined Y-type crystalline phase is formed. It is observed that DC resistivity enhanced which is accredited to room temperature resistivity differences of dopant and host ions. The hopping of electrons and jumping of holes are responsible for conduction below Curie temperature (TC), whereas above Curie temperature is due to polaron hopping. The decrease in TC may be due to the fact that Eu–Fe interactions on the B sites are weaker than Fe–Fe interaction. The dispersion in the dielectric constant ɛ′(f) favor the occurrence of peaks in the tanδ(f). The extraordinary values of resistivity and small dielectric loss make these materials pre-eminent contestant for high frequency applications.

Research on Mechanical Design with Beidou GPS Navigation Antenna Design Terminal

With advances in technology and machinery manufacturing technology, the satellite navigation system plays a more and more important role in the modern society. People demand increasingly for satellite navigation. Satellite navigation is increasingly used in military systems, so military and civilian value is higher and higher. For the satellite signal reception, microstrip antenna plays an indispensable role. As the mechanical design of microstrip antenna is simple, easy manufacture, low cost, smaller size, lighter weight, with the overall unity of active devices and integrated circuit, etc. The successful development of high dielectric constant ceramic material enables the area of microstrip antenna to narrow several times. Microwave dielectric ceramics material has some merits such as high dielectric constant, thermal stability and excellent characteristics of small dielectric loss. Different dielectric constant substrate can be prepared through changing and doping modification of process parameters, including the relative dielectric constant of microwave dielectric ceramics for more than a few dozens which can be used for different microwave frequencies. Those are important reasons for promoting the development of microstrip antenna.

Linear and quadratic magnetoelectric effect in CNMFO:PZT magnetoelectric composite

Dynamic magnetoelectric voltage measurements of 30 % Co0.7−xNixMn0.3Fe2O4:70 % Pb(Zr0.52Ti0.48)O3 composites with x = 0.00, 0.05, 0.10, 0.15 synthesized by ceramic method were carried out by linear and quadratic method. Maximum linear magnetoelectric coefficient (α) of 14.7 mv Oe−1 cm−1 and maximum quadratic coefficient (β) of 2.26 × 10−4 mv Oe−2 cm−1 were obtained for composition with x = 0.05. Maximum values of α and β for composition with x = 0.05 may be due to more connectivity between grains than in other compositions observed from scanning electron micrographs. Higher values of dielectric constant and ac conductivity for particular composition could also be possible reasons for maximum magnetoelectric coefficients. Smaller dielectric loss at higher frequencies was observed for the same composition which may result into less leakage of charges consequently increasing the resultant magnetoelectric coefficients.

Yttrium Iron Garnet: Properties and Applications Review

Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material to be used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. This work presents the study of the ferrimagnetic composite, constituted by Y3Fe5O12 (YIG) and Gd3Fe5O12 (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screen-printing technique), in the microwave frequency range. The experiments with FRAs showed satisfactory results due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.

Piezoelectric Properties of Lead‐free Piezoelectric Ceramics and Their Energy Harvester Characteristics

The energy convergence efficiency (η) and dimensionless figure of merit (DFOM) of CuO‐added (Na0.5K0.5)NbO3 (CNKN) ceramics are larger than those of NKN ceramics because of their large Qm values and small dielectric losses. Moreover, the η and DFOM values of CNKN ceramics are comparable to those of P‐5C ceramics, which exhibit the highest η and DFOM. Furthermore, the CNKN harvester exhibits a high power density of 12 mW/cm3 at 93 Hz with a load resistance of 250 kΩ; this is similar to the PZT‐based energy harvester, indicating that the CNKN ceramic is a good candidate material for energy harvesters.

Microwave complex permittivity of voltage-tunable nematic liquid crystals measured in high resistivity silicon transducers

A split post dielectric resonator is used to determine the effect of AC bias voltage on the microwave complex permittivity of nematic liquid crystals. High resistivity silicon transducers separated by 100 μm are bridged by nematic liquid crystals and their properties determined. The in-plane permittivity of liquid crystals can be effectively tuned (change of effective permittivity of up to 8%) by increasing the AC bias voltage from 0 to 6 V. Using high resistivity silicon allowed us to obtain tunable dielectric stacks with relatively small dielectric losses at microwave frequencies.

The effect of Mg doping on the dielectric and tunable properties of Pb0.3Sr0.7TiO3 thin films prepared by sol–gel method

Mg doped Pb0.3Sr0.7TiO3 (PST) thin films were fabricated by the sol–gel method on a Pt/Ti/SiO2/Si substrate. The microstructure, surface morphology, dielectric and tunable properties of PST thin films were investigated as a function of Mg concentration. It is found that proper Mg doping dramatically improves the dielectric loss (0.0088 @ 1 MHz), furthermore, the crystallinity, dielectric constant, and tunability of films simultaneously decrease with the increase of Mg content. The 2 mol% Mg doped PST thin film shows the highest figure of merit (FOM) value of 36.8 for its the smallest dielectric loss and upper tunability. The dependence of Rayleigh coefficient on the doping concentration was examined, which indicated that the reduction of dielectric constant and tunability of films should be related to the \(\mathrm{Mg}''_{\mathrm{Ti}}\)–\(\mathrm{V}_{\mathrm{O}}^{\bullet\bullet}\) defect dipoles pinning the domain wall motion of residual polar clusters in PST.

Dielectric composites with a high and temperature-independent dielectric constant

Dielectric composites made using P(VDF-CTFE) 88/12 mol% as polymer matrix and both micro-sized and nano-sized CaCu3Ti4O12 (CCTO) particles as filler are developed. These composites exhibit high dielectric constant with a small dielectric loss. More importantly, it is found that the dielectric constant of these composites is almost independent of temperature from 25 °C to 125 °C. Comparing the composites made using micro-sized CCTO particles, the composites made using nano-sized CCTO particles exhibit a smaller dielectric loss. The dielectric properties of these composites indicate that the nano-sized CCTO particles have a smaller dielectric constant than the micro-sized CCTO particles.

Enhanced the Dielectric and Tunable Properties of BZNT Thin Films through Adjusting Annealing Process

Bismuth zinc niobate titanium (Bi1.5Zn0.5 Nb0.5Ti1.5O7) (BZNT) thin films were deposited on PtTiSiO2Si substrates by radio frequency (rf) magnetron sputtering. The microstructure, surface morphology, stress, dielectric and tunable properties of thin films were investigated as a function of initial annealing temperature. It’s found that high initial annealing temperature increases the grain size, dielectric constant and tunability of BZNT films simultaneously and decreases the tensile stress in films. The BZNT thin film annealed from 500 °C to 700 °C shows the highest FOM value of 45.67 with the smallest dielectric loss and upper tunability.

The microstructure and properties of Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) x O3 ceramic system

The microstructure and dielectric properties of Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) x O3 (x=0, 0.04, 0.08, 0.12, 0.16) ceramic system were investigated. The Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) x O3 ceramics were prepared by the traditional solid-state reaction method and were characterized by X-ray diffraction (XRD), scanning electron microscopy(SEM) and Raman spectrometer. The sintering ability and dielectric properties of Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) x O3 were found to be improved with the doping of Mn4+ and W6+ ions. The densification temperature of Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) x O3 ceramics decreased from 1 080 °C to 1 000 °C when x increased from 0 to 0.16. Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) x O3 ceramic was found to have the best dielectric properties when x=0.08, larger permittivity (ɛ=547) and smaller dielectric loss (tanδ=0.00156).