Dielectric properties of barium titanate–molybdenum composite

The barium titanate–molybdenum composites were prepared through solid state reaction method in argon atmosphere. The microstructure, resistivity, and dielectric properties of the composites were investigated. XRD results indicated that chemical reactions between barium titanate (BaTiO₃:BT) and molybdenum (Mo) have taken place during sintering, resulting in the formation of BaMoO₄ (BM) and BaTi₂O₅ (BT₂). The resistivity decreased with the increasing amount of Mo in the composites. The composites (when x = 5 and 20 wt.%) showed lower dielectric constant than pure BaTiO₃, especially, the dielectric constant (when x = 20 wt.%) reached a minimum value (<10⁴), while composites (when x = 10 and 15 wt.%) showed rather high dielectric constant at temperatures range from 25 °C to 160 °C. The dielectric constant of the composite gradually decreased with increase in frequency at the room temperature. The dielectric constant of composite (when x = 5 wt.%) comes up to 10⁴, and the T_c (Curie temperature) of the composite was relatively higher than that of BT (120 °C).     

Crystal structure and dielectric properties of barium titanate–kaolinite composites

Barium Titanate–Kaolinite composites were prepared systematically by conventional solid-state method. The crystal structure and dielectric properties of samples were investigated by XRD and dielectric measurements, respectively. XRD results show that new phase BaAl₂Si₂O₈ was formed as kaolinite added into BaTiO₃. The 10 wt% kaolinite addition led to a considerable reduction in sintering temperature and a strong densification. The dielectric constant of BaTiO₃–Kaolinite composites tended to be stable with increasing of kaolinite content.     

Tunability and microwave dielectric properties of BaO–SrO–Nd2O3–TiO2 ceramics

Ferroelectrics such as barium–strontium titanates (BSTO) and Mg-doped BSTO are well known as promising candidates for the application in microwave tunable devices including phase shifters, filters, and others operating at microwave frequencies. In this study new bulk ceramics based on BaTiO₃ (BTO)–SrTiO₃ (STO) with addition of BaNd₂Ti₄O₁₂ (BNT) solid solution was investigated. The phase correlations, size, and nature of boundaries between phases were studied using scanning electron microscopy (SEM). The effect of compositional change on the unit cell parameters of the perovskite phase, microwave dielectric properties, and tunability under DC field had been studied. The materials with dielectric constant ∼320–700, Qf = 1950–3000 GHz at 3.5 GHz and tunability ∼8.0–31.7% at E = 1 V/μm were achieved.     

Piezoelectric and dielectric properties of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3–PVDF composites

(Li, Ta, Sb) modified sodium potassium niobate/poly(vinylidene fluoride) [(K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃–PVDF] 0-3 composites were prepared by a cold press technique, and their piezoelectric and dielectric properties were characterized. All composites exhibited good dispersion of ceramic particles in the polymer matrix. The piezoelectric and dielectric constants were found to be enhanced as the concentration of sodium potassium niobate increases. Even though the process is simple, the composite prepared in this study showed better piezoelectric and dielectric properties than PZT–polymer composites. At room temperature, a (K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃–PVDF (7:3) composite revealed a relative dielectric constant, ?_r = 166, piezoelectric constant, d₃₃ = 33 pC/N and coercive field, E_c = 5 kV/cm.     

Dielectric constant and energy density of poly(vinylidene fluoride) nanocomposites filled with core-shell structured BaTiO3@Al2O3 nanoparticles

Ceramics-polymer nanocomposites consisting of core-shell structured BaTiO₃@Al₂O₃ (BT@Al₂O₃) nanoparticles as the filler and poly(vinylidene fluoride) (PVDF) as the polymer matrix were fabricated by solution casting. At the same volume fraction, the BT@Al₂O₃/PVDF nanocomposites, with larger dielectric constant and higher energy density, outperformed the BT/PVDF nanocomposites. The 2.5 vol% BT@Al₂O₃/PVDF nanocomposites at 360 MV/m had a double more energy density than pure PVDF at 400 MV/m (6.19 vs. 2.30 J/cm³), and a remarkably 42% lower remnant polarization than the 2.5 vol% BT/PVDF nanocomposites (0.99 vs. 1.69 μC/cm² at 300 MV/m). Such significant enhancement was closely related to the surface modification by Al₂O₃, which improved the insulation of BT nanoparticles and reduced the contrast of dielectric constant between the filler and the PVDF matrix.     

Nano-sized Ag–BaTiO3 composite powders with various amount of Ag prepared by spray pyrolysis

The preparation of precursors of BaTiO₃ nanopowders with various amounts of Ag by spray pyrolysis is reported. The precursor powders obtained with hollow and thin-wall particles are composed of uniformly dispersed Ba, Ti, and Ag components. After post-treatment and a simple milling process, the precursor powders, irrespective of the amount of Ag, are transformed into Ag–BaTiO₃ composite nanoparticles. The mean particle size of the Ag (10 mol%)–BaTiO₃ powders is 142 nm. BaTiO₃ pellets containing Ag exhibit dense structures even at a low sintering temperature of 1000 °C. BaTiO₃ pellets with 10 mol% Ag show the highest dielectric constant of 2950, as opposed to the pure BaTiO₃ pellets (without Ag), whose dielectric constant is 1827.     

Doping behaviors of NiO and Nb2O5 in BaTiO3 and dielectric properties of BaTiO3-based X7R ceramics

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 (Ni_1/3²⁺Nb_2/3⁵⁺)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.     

Electrical properties of low-temperature-fired ferrite–dielectric composites

The effects of the BaO·(Nd_0.8Bi_0.2)₂O₃·4TiO₂ (BNBT) to NiCuZn ferrite ratio and addition of Bi₂O₃–B₂O₃–SiO₂–ZnO (BBSZ) glass on the sintering behavior, microstructure evolution, dielectric and magnetic properties of BNBT–NiCuZn ferrite composites were investigated in developing low-temperature-fired composites for high frequency electromagnetic interference (EMI) devices. The results indicate that these composites can be densified at 900 °C and exhibit superior dielectric and magnetic properties with the addition of BBSZ glass. The dielectric system used in the ferrite–dielectric composites reported in the previous studies mostly belong to the ferroelectricity group, which are not suitable for use in the high frequency range (>800 MHz) due to the selfresonance frequency limit. In this study, the dielectric constant remains nearly a constant over a wide range of frequencies (100 MHz to 1 GHz) and the magnetic resonance frequencies are larger than 100 MHz for the BNBT + BBSZ glass–NiCuZn ferrite composites. Therefore, the BNBT + BBSZ glass–NiCuZn ferrite composites can be a good candidate material for high frequency EMI device applications.     

The dielectric properties of BaTiO3 based ceramics co-doped with Bi/Mn

BaTiO₃ based ceramics (with some additives such as ZrO₂, SnO₂, etc.) were prepared by solid state reaction. Mn²⁺ or Mn³⁺ as an acceptor substituting for Ti⁴⁺ in B site and Bi³⁺ as a donor substituting for Ba²⁺ in A site were co-doped in BaTiO₃ based ceramics. The dielectric properties of BaTiO₃ based ceramics co-doped with Bi/Mn were investigated. The results show that the dielectric properties of BaTiO₃ based ceramics co-doped with Bi/Mn are affected by the mole ratio of donor and acceptor (Bi/Mn). When the mole ratio of donor and acceptor is high, dielectric dispersion behavior was observed and the dielectric constant decrease and remnant polarization, coercive field and piezoelectric constant will varied. When Bi varied from 1.0% to 2.0 mol% (Mn = 0.8 mol%), remnant polarization from 10.35 to 2.25 μC/cm², coercive field from 4 to 2.75 kV/cm, and piezoelectric constant d₃₃ from 137 to 36 pC/N respectively.     

Significant enhancement in breakdown strength and energy density of the BaTiO3/BaTiO3@SiO2 layered ceramics with strong interface blocking effect

The BaTiO₃/BaTiO₃@SiO₂ (BT/BTS) ceramics with layered structure, where grain size was about 1–2 μm in the BT layer while it was about 300–400 nm in the BTS layer, were fabricated by the tape-casting and lamination method. With the increasing of SiO₂ content in the BTS layer, the dielectric constant decreased gradually, and the breakdown strength was remarkably improved. Compared to the SiO₂-added BaTiO₃ bulk ceramics, the layered ceramics displayed significant enhancements in dielectric properties, breakdown properties and energy storage properties. The enhancement in dielectric properties was mostly attributed to the diluting effects created by this structure to SiO₂. Based on the finite element analysis with the dielectric breakdown mode, it was regarded that the electric field redistribution and the interface blocking effect led to the enhancement of breakdown strength. Finally, the maximum energy density of 1.8 J/cm³ was obtained at a breakdown strength of 301.4 kV/cm for the BT/BTS3 ceramic.     

Dielectric relaxation properties of PbTiO3-multiwalled carbon nanotube composites prepared by a sol–gel process

Dielectric composites fabricated by combining multi-walled carbon nanotubes (MWCNT) and PbTiO₃ (PTO) powder were prepared using a sol–gel process. Well-dispersed PTO powder with various volume ratios of MWCNT was compressed to form a pellet, and then silver electrodes were coated on both sides for electrical measurements. The PTO–MWCNT composite with 0.4 vol% MWCNT showed the highest dielectric constant (912 at 1 kHz), which is approximately 25 times larger than that (37 at 1 kHz) of a pure PbTiO₃ pellet. Furthermore, a strong frequency dependence of the dielectric constant in the low frequency range was shown for the PTO–MWCNT composites. Interfacial effects related to dielectric relaxation in composite materials were used to explain an observed increase of the dielectric constant near the percolation threshold.     

Microstructure and electrical properties of BaTiO3/Cu ceramic composite sintered in nitrogen atmosphere

BaTiO₃/xCu composite ceramics with x = 0–30 wt.% were fabricated by the traditional mixing oxide method and their microstructure, relative density, electric conductivity, permittivity and dielectric loss were measured as a function of the Cu mass fraction. The X-ray diffraction (XRD) patterns indicated that the dense composite has no chemical reaction between BaTiO₃ and Cu during sintering, and the relative diffraction intensity of Cu increased with the increase of Cu. The electric properties showed that the percolation threshold of BaTiO₃/Cu composites was x = 0.25 and its conductivity increased as the Cu content increased after that. With increasing Cu content up to 30 wt.%, the permittivity (?_r) markedly increased from ～3000 for monolithic BaTiO₃ to ～8000 at 1 kHz. Additionally, the temperature coefficient of this system was less than 5% in the temperature range of 25–115°C.     

Effects of K0.5Bi0.5TiO3 addition on dielectric properties of BaTiO3 ceramics

(1?x)BaTiO₃–xK_0.5Bi_0.5TiO₃ (abbreviated as BT–KBT, 0.10≦x≦0.15) dielectric ceramics were prepared by a conventional oxide mixing method. The effects of KBT content on the densification, microstructure and dielectric properties of BT ceramics were investigated. The density characterization results show that the addition of KBT significantly lowered the sintering temperature of BT ceramics to about 1280 °C. The XRD results showed that the phase compositions of all samples were pure tetragonal phases. The dielectric constant and dielectric loss firstly increased and then decreased with the increase of KBT. In addition, dielectric constant and dielectric loss versus frequency were characterized in the frequency range from 100 Hz to 2 MHz. It is found that the dielectric constant and the dielectric loss changed with the increase of KBT contents regularly.     

Giant permittivity phenomena in layered BaTiO3–Ni composites

Layered BaTiO₃–Ni cermet composites with a constant composition but diversified microstructures were produced by a rolling-and-folding processing method. These composites differ from conventional laminates in that their interface has a tendency to be wavy, with a globular or elongated second phase within a continuous matrix phase. Based on an analysis of the (di)electric properties and Monte Carlo simulations we confirmed the critical influence of the composite's microstructural characteristics on the percolation threshold. We found that the dielectric properties of the composite, when it is in the insulation regime, were controlled by the insulating BaTiO₃ phase. A giant effective permittivity of around 200 000, with modest losses of tan δ < 0.04, was measured when the percolation threshold approached the composition of the cermet. Partial decomposition and deformation of the layered structure resulted in the creation of conducting paths, whereas further homogenization again shifted the percolation threshold above the actual composition of the cermet.     

Dielectric behaviors of Nb2O5–Co2O3 doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics

Nb₂O₅ and Nb–Co doped 0.85BaTiO₃–0.15Bi(Mg_1/2Ti_1/2)O₃ (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb₂O₅/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb₂O₅ was found to possess a moderate dielectric constant (? ～ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from ?55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.     

Percolative BaTiO3–Ni composite nanopowders from alkoxide-mediated synthesis

BaTiO₃–Ni nanopowders have been synthesized via an alkoxide-mediated synthesis route through the hydrolysis and condensation of barium hydroxide octahydrate and titanium (IV) isopropoxide in the presence of submicron sized, spherical Ni particles originating from a commercial Ni paste, that was introduced during the preparation procedure. X-ray diffraction (XRD) patterns indicate that nanocomposite powders of the phases BaTiO₃ and Ni could be successfully prepared and tailor-made composition control was confirmed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the synthesized BaTiO₃ nanoparticles were aggregates of nanosized primary particles as small as 40 nm in diameter. The average Ni particle size was estimated to be about 200 nm. Dilatometric measurements on green compacts of these powders revealed that the shrinkage of BaTiO₃–Ni composites is retarded compared to both, pure BaTiO₃ and Ni. Thermogravimetric analysis (TGA) shows weight losses due to the decomposition of organic binder from Ni paste, the release of water from the surface and of hydroxyl ions from inside the lattice of the BaTiO₃ nanoparticles. With the addition of nickel, the dielectric constant increased slightly due to the percolation effect.     

Dielectric and magnetoelectric properties of BaTiO3–Co0.6Zn0.4Fe1.7Mn0.3O4 composite

In this paper we studied the structural, dielectric, magnetic and magnetoelectric properties of (x)BaTiO₃–(1 ? x)Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ particulate composite series where x = 0.50, 0.60 and 0.70. BaTiO₃–Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ composite has the advantage of being non-toxic and environmental friendly from the point of view of device fabrication. High ME voltage coefficients were obtained in the whole series with the highest value of α_E ～ 73 mV/cm Oe achieved in sample x = 0.50 containing equal mole fractions of both the component phases. This value of α_E is an order of magnitude higher than that of particulate sintered BaTiO₃–CoFe₂O₄ composites (～2–4 mV/cm Oe). Dielectric characteristics for these samples indicated two anomalies: (i) one at low temperature close to ferroelectric to paraelectric transition temperature of pure BaTiO₃ and (ii) another at higher temperature related to the magnetic transition in ferrite, a characteristic dielectric feature of composite sample.     

Studies of dielectric properties of rare earth (Dy,Tb, Eu) doped barium titanate sintered in pure nitrogen

This paper investigated dielectric properties of rare earth (Dy, Tb, Eu)-doped barium titanate sintered in pure nitrogen. The substituting concentration of rare earth (Dy, Tb, Eu) was 2.0 mol%. The doping behaviors of intermediate rare-earth ions (Dy, Tb, Eu) and their effects on the dielectric property of barium titanate were investigated. Eu³⁺ ion was substituted in the A-site of the perovskite lattice. Dy³⁺ and Tb³⁺ ions substituted partially for Ti⁴⁺ site and partially for Ba²⁺ site. The different rare earth element had a crucial effect on dielectric properties of rare-earth-doped BaTiO₃. Among these doped samples, Tb-doped BaTiO₃ had the largest dielectric constant (70,000–80,000); the smallest dielectric loss (less than 4%), and good capacitance-temperature coefficient, which satisfies the X7R specification of the Electronic Industries Association Standards (TCC within ±15% from ?55 °C to 125 °C).     

Preparation and characterization of lead-free (K0.47Na0.51Li0.02)(Nb0.8Ta0.2)O3 piezoceramic/epoxy composites with 0–3 connectivity

Lead-free (K_0.47Na_0.51Li_0.02)(Nb_0.8Ta_0.2)O₃ (KNLNT) piezoceramic/epoxy composites with 0–3 connectivity were prepared using cold-pressing. The dielectric and piezoelectric properties of the composites were examined as a function of mean particle size (D) within the range of 27–174 μm at a fixed ceramic content of 85 vol%. The dielectric constant increased with D by the combined effects of increased connectivity and decreased surface-to-volume ratio of ceramics. When D = 125 μm, the piezoelectric constant showed a highest value of 44 pC/N that is much greater than those of previous reports on lead-free piezoelectric 0–3 ceramic/polymer composites.     

Extrinsic behavior in La0.67Ca0.33MnO3–BaTiO3 composites

A manganite matrix based nano-composite series, (1 ? x)La_0.67Ca_0.33MnO₃(LCMO)–(x)BaTiO₃(BTO), has been prepared by the pyrophoric method. Influence of BTO phase on structural and magneto-transport properties of LCP phase has been studied using structural and transport investigations. The series exhibits a conduction threshold at x_m ～ 0.30. Overall pattern of temperature dependence of resistivity for this series has been fitted with a percolation model. Almost 200% improvement has been observed by the formation of composite when compared to the parent sample.