Characterization of Ba4.5Re9Ti18O54 (Re = La,Nd) microwave dielectric ceramics

Ba_4.5Re₉Ti₁₈O₅₄ (Re = La, Nd) ceramics were prepared via a solid state mixed oxide route. X-ray diffraction (XRD) analysis revealed the formation of the major Ba_4.5Re₉Ti₁₈O₅₄ phase along with rutile (TiO₂) as a secondary phase. Rietveld structure refinement of the recorded XRD data confirmed that the crystal structure of Ba_4.5Nd₉Ti₁₈O₅₄ (BNT) was orthorhombic (Pnma) with unit cell parameters a = 22.3412 Å, b = 7.6824 Å and c = 12.1952 Å. Ba_4.5La₉Ti₁₈O₅₄ (BLT) exhibited high relative permittivity (95.6), low quality factor (2,102 GHz) and a high temperature coefficient of resonance frequency (+352 ppm/°C). The substitution of Nd for La caused a decrease in both the relatively permittivity and temperature coefficient of resonance frequency to 84.2 and 167 ppm/°C respectively and an increase in quality factor to 8,007 GHz. Raman spectroscopic analysis revealed that lattice defects may be responsible for the observed decrease in quality factor of BLT ceramics in comparison to BNT. The Raman shifts at 533.5 and 613.6 cm^?1, related to Ti–O bond stretching, decreased for BNT ceramics, which may be a possible reason for the observed decrease in relative permittivity.     

Structure and dielectric properties of Nd x Sr1−x TiO3 ceramics for energy storage application

Polycrystalline Nd-doped SrTiO₃ ceramics with the formula Nd _x Sr_1?x TiO₃ (NSTO, x = 0, 0.024, 0.056, 0.104, 0.152, 0.200) were prepared by solid state reaction route. X-ray diffraction (XRD) analysis confirmed the formation of monophasic compounds and indicated the structure to be changed from cubic to tetragonal by increasing Nd doping concentrations. A remarkable decrease in grain size from ~30 μm for un-doped SrTiO₃ ceramics to ~1 μm for Nd-doped SrTiO₃ ceramics with x = 0.024 was observed by scanning electron microscopy. The grain size had a degree of increasing with further increasing Nd doping concentration and reached ~3 μm when the x value was 0.200. The dielectric properties of NSTO ceramics were measured at 1 kHz in ambient temperature. It revealed that the dielectric constant dramatically increases for the reason of Nd doping, leading to a maximum value of 19,800 for as-sintered sample with x = 0.104. The breakdown strength of all Nd-doped SrTiO₃ samples was found to be higher than 10 kV/mm. The relationship between dielectric properties and the microstructure feature, as well as the defect structures correlated with the charge compensation induced by trivalent Nd³⁺ doping, was discussed tentatively.     

Dielectric and electrical energy storage properties of BiFeO3–BaTiO3–SrTiO3 ternary bulk ceramics

Journal of Materials Science: Materials in Electronics - Recently, it is shown that the thin films of BiFeO3–BaTiO3–SrTiO3 have ultrahigh-energy storage density. However, the energy...     

Physical and electrical properties of MnO2-doped Pb(Zr x Ti1−x )O3 ceramics

The effects of composition on the physical property change in the phase coexistence region between the tetragonal and rhombohedral phases have been investigated as a function of zirconium concentration, x, for the MnO₂-doped Pb(Zr _x Ti_1–x )O₃ (0.40x0.60) ceramics. The relative amount of phase coexisting between the tetragonal and rhombohedral phases affects greatly both dielectric and piezoelectric properties as a function of zirconium concentration. However, there are no detectable changes between the apparent density and microstructure. Also, in the coexistence region, the relative amount of coexistence of the rhombohedral phase increases with MnO₂ addition. The inflection points of the dielectric constant shift to lower zirconium concentration in proportion to the MnO₂ addition, owing to the substitution effect on the PZT lattice site.     

Microstructure and electrical properties of Dy2O3-doped ZnO–Pr6O11-based varistor ceramics

The microstructure and electrical properties of varistor ceramics, in the ZnO–Pr₆O₁₁–CoO–Cr₂O₃–Dy₂O₃ (ZPCCD) system, were investigated in the range of 0.0–2.0 mol% Dy₂O₃. The Dy₂O₃ microstructurally played the role of inhibition in the densification and grain growth. As Dy₂O₃ content is increased, the density was decreased in the range of 5.49–4.64 g/cm³, and the average ZnO grain size was decreased in the range of 18.2–4.6 μm. The incorporation of Dy₂O₃ significantly improved the nonlinear properties of ZPCCD-based varistor ceramics, above 45 in the nonlinear exponent compared with that without Dy₂O₃. The varistor ceramics with Dy₂O₃ content of 0.5 mol% exhibited the best performance, with 5.49 g/cm³ in density, 55.3 in nonlinear exponent, and 0.1 μA in leakage current.     

Microstructure and dielectric properties of Ca1–3/2xBixCu3Ti4O12 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics

Influence of bismuth substitution on calcium site in CaCu₃Ti₄O₁₂ has been investigated. Compositions of Ca_1-3/2xBi_xCu₃Ti₄O₁₂ (x = 0, 0.05, 0.10, 0.15 and 0.20) were fabricated by solid-state sintering method. Crystal structure is remained cubic. X-ray diffraction indicates the presence of secondary phase of CuO in CCTO ceramics. Bismuth doping restrains the formation of CuO phase apparently. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by Bi³⁺ doping, resulting from the ability of bismuth to inhibit the grain growth. The dielectric and electric properties of CCTO ceramics were found to be influenced by bismuth doping. The fitting results of the complex impedance spectra showed an increase of the resistance of grain and grain boundary by bismuth substitution. Ca_0.70Bi_0.20Cu₃Ti₄O₁₂ showed the highest dielectric constant in the low frequency range. A modest composition such as Ca_0.85Bi_0.10Cu₃Ti₄O₁₂ expressed the optimized dielectric properties of higher dielectric constant (1.3 × 10⁴) and lower dielectric loss (0.06) than pure CCTO. The low and high temperature dielectric loss spectra demonstrate the interfacial polarization of the initial and secondary oxygen ionization, relating with the grain and grain boundary (the electrode contact for Ca_0.70Bi_0.20Cu₃Ti₄O₁₂) respectively.     

Dielectric behavior and energy storage properties in BaO–SrO–Nb2O5–B2O3 system glass–ceramics with Gd2O3 addition

A series of strontium barium niobate-based borate system glass–ceramics with Gd₂O₃ addition have been prepared by controlled crystallization method. The effect of Gd₂O₃ addition on the microstructure, phase evolution and dielectric properties has been investigated. The results show that the addition of Gd₂O₃ to the glass–ceramics changes the dielectric property and energy-storage density. Typically, the glass–ceramics with 0.5 mol% Gd₂O₃ heat treated at 630 °C/2 h + 800 °C/3 h possesses a dielectric constant of 136, a breakdown strength of 1,075 kV/mm and energy-storage density of 6.94 J/cm³, which is suitable for the application in high energy-storage capacitors.     

Preparation and thermophysical properties of nano-sized Ln2Zr2O7 (Ln?=?La, Nd, Sm, and Gd) ceramics with pyrochlore structure

Rare earth zirconates (Ln₂Zr₂O₇, Ln = La, Nd, Sm, and Gd) with pyrochlore structure were prepared by hydrothermal method with polyethylene glycol as surfactant. X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy were utilized to characterize the phase structure, thermal decomposition, and morphology of the products. Qualitative analysis indicates that the as-prepared zirconates are pyrochlore-type structures. The specific surface area, lattice parameter, and average crystallite size of the as-prepared products are closely related to the ionic radius. The activation energy of crystal growth shows an increasing trend with the decrease in ionic radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties of Ln₂Zr₂O₇ are descending as the order of La₂Zr₂O₇, Nd₂Zr₂O₇, Sm₂Zr₂O₇, and Gd₂Zr₂O₇.     

Structural,dielectric, and ferroelectric properties of BaTiO3–Bi(Ni1/2Ti1/2)O3 lead-free ceramics with remarkable energy storage performance under low electric fields

Journal of Materials Science: Materials in Electronics - In order to fabricate high-performance dielectric capacitors for pulsed power applications,...     

Microwave dielectric properties and microstructures of Nd(Mg0.5?xCoxSn0.5)O3 ceramics

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5?xCo_xSn_0.5)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5?xCo_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.45Co_0.05Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (? _r ) of 19.2, a quality factor (Q?×?f) of 68,900?GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?67?ppm/°C were obtained for Nd(Mg_0.45Co_0.05Sn_0.5)O₃ ceramics that were sintered at 1,550?°C for 4?h.     

Structure,morphology, sintering behavior,and microwave dielectric properties of 6Ca0.61Nd0.26TiO3–4Nd(Zn1/2Ti1/2)O3 ceramics prepared via citrate precursor method

Journal of Materials Science: Materials in Electronics - This paper reports a controllable synthesis of 6Ca0.61Nd0.26TiO3–4Nd(Zn1/2Ti1/2)O3 (6CNT–4NCT) nanopowders by the citrate...     

Structure and properties of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 solid solution ceramics

The widely used piezoelectric Pb(Zr_1−x Ti _x )O₃ ceramics have been known to have Zr⁴⁺ and Ti⁴⁺ randomly distributed on the B-site lattice in the ABO₃ perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg_1/2W_1/2)O₃ − xPb(Zr_0.5Ti_0.5)O₃ (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg_1/2W_1/2)O₃ and the ferroelectric order in Pb(Zr_0.5Ti_0.5)O₃ leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, T _m, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties.