Effect of sintering temperature on electrical properties, dielectric characteristics, and aging behavior of ZnO–V2O5-based varistor ceramics modified with Bi2O3

The effect of sintering temperature on microstructure, electrical properties, dielectric characteristics, and aging behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅–Bi₂O₃ varistor ceramics was systematically investigated at 875–950 °C. The sintered density decreased from 5.50 to 5.34 g/cm³ and the average grain size increased from 5.4 to 15.0 μm with an increase in the sintering temperature. The breakdown field (E_B) decreased from 5,785 to 1,181 V/cm with an increase in the sintering temperature. The varistor ceramics sintered at 900 °C exhibited a surprisingly high nonlinear coefficient (α = 61). The donor concentration (N_d) increased from 2.08 × 10¹⁷ to 4.64 × 10¹⁷ cm^?3 with an increase in the sintering temperature and the barrier height (Φ_b) exhibited 1.08 eV as the maximum value at 900 °C. Concerning stability, the varistors sintered at 950 °C exhibited the strongest accelerated aging characteristics, where %ΔE_B = ?1.4 % and %Δα = ?14.6 % for DC accelerated aging stress of 0.85 E_B/85 °C/24 h.     

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 microwave dielectric characteristics of CaO–B2O3–SiO2 glass ceramics

CaO–B₂O₃–SiO₂ (CBS) glass powders are prepared by traditional glass melting method, whose properties and microstructures are characterized by Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the pure CBS glass ceramics possess excellent dielectric properties (ε _r = 6.5, tan δ = 5 × 10⁻³ at 10 GHz), but a higher sintering temperature (>900 °C) and a narrow sintering temperature range (about 10 °C). The addition of a low-melting-point CaO–B₂O₃–SiO₂ glass (LG) could greatly decrease the sintering temperature of CBS glass to 820 °C and significantly enlarge the sintering temperature range to 40 °C. The CBS glass ceramic with 30 wt% LG glass addition sintered at 840 °C exhibits better dielectric properties: ε _r ≈ 6, tan δ < 2 × 10⁻³ at 10 GHz, and the major phases of the sample are CaSiO₃, CaB₂O₄ and SiO₂.     

Microstructure and dielectric properties of BF–PFN ceramics with negative dielectric loss

Multiferroics with negative value of dielectric constant are very promising materials because of their modern applicability. These materials can be used as materials for the construction of electromagnetic radiation shields. The subject of the research is multiferroic BiFeO₃–PbFe_1/2Nb_1/2O₃ (BF–PFN) ceramics. For all multiferroic materials the following studies are conducted: SEM, EDS and the temperature dependence of dielectric constant ε′(T). Above a certain temperature (different for different chemical compositions) the value of dielectric constant reaches negative values. Such the behavior of the dielectric constant may indicate that the polarization inside the material has a reverse direction to the external electric field. That is, the electric field inside the material counteracts the applied external electric field. The obtaining materials also show negative dielectric losses. The Axelrod model is used to explain the mechanism that causes negative dielectric loss.     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

SbVO4 doped ZnO–V2O5-based varistor ceramics: microstructure, electrical properties and conductive mechanism

The effects of SbVO₄ addition on the microstructure, electrical properties and characteristics of grain and grain boundary of ZnO–V₂O₅ based varistor ceramics were studied using SEM, E–J measurements and impedance spectroscopy. XRD analysis revealed that all the samples consist of main phase of ZnO and the second phase of BiVO₄ and Zn₇Sb₂O₁₂. The microstructural homogeneity of the ceramic was improved through adding SbVO₄. With an increase of SbVO₄, the average grain sizes decrease from 16.1 to 6.1 μm. The resistivity of grain boundary is approximately constant (~10³ Ω). The ZnO–V₂O₅-based varistor ceramics added with 0.3 mol % SbVO₄ sintered at 940 °C for 4 h exhibited good nonlinear properties of α = 51, J = 13.4 μA/mm² and E _1mA = 416 V/mm.     

Effect of sintering process on electrical properties and ageing behavior of ZnO–V2O5–MnO2–Nb2O5 varistor ceramics

The effect of sintering process on microstructure, electrical properties, and ageing behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅ (ZVMN) varistor ceramics was investigated at 875–950 °C. The sintered density decreased from 5.52 to 5.44 g/cm³ and the average grain size increased from 4.4 to 9.6 μm with the increase of sintering temperature. The breakdown field (E_{1 mA}) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 °C led to surprisingly high nonlinear coefficient (α = 50). The donor concentration (N_d) increased from 3.33 × 10¹⁷ cm⁻³ to 7.64 × 10¹⁷ cm⁻³ with the increase of sintering temperature and the barrier height (Φ_b) exhibited the maximum value (1.07 eV) at 900 °C. Concerning stability, the varistors sintered at 925 °C exhibited the most stable accelerated ageing characteristics, with %ΔE_{1 mA} = 1.5% and %Δα = 13.3% for DC accelerated ageing stress of 0.85 E_{1 mA}/85 °C/24 h.     

Microstructure and electrical properties of Ni–Zn manganite ceramics

Nickel zinc manganite ceramics Mn_2.34−xNi_0.66Zn_xO₄ (0≤x≤1.02) were investigated using structure, microstructure and electrical property interrelationships. The resistivity increased with zinc content whereas the activation energy remained constant. The drift of resistivity under thermal constraint, commonly observed in NTC thermistors was almost nil when the zinc content was sufficiently high (x≥0.7). Homogeneous microstructures and high densities were obtained when the ceramics were prepared from fine powders. The Ni/Zn/Mn/O system prepared by ‘chimie douce’ has interesting NTC properties for industrial applications.     

Improvement of aging characteristics of (Mn, Nb, Er)-doped ZnO–V2O5-based varistor ceramics by small sintering changes

This paper focuses on that the aging characteristics for (Mn, Nb, Er)-doped ZnO–V₂O₅-based varistor ceramics could be controlled by small sintering change. Small change in the sintering temperature did have a noticeable effect on the DC aging characteristics as well as initial electric field-current density (E–J) characteristics. As the sintering temperature increased, the average grain size increased from 4.3 to 9.0 μm, whereas the sintered density decreased from 5.57 to 5.47 g/cm³. The breakdown field and the nonlinear coefficient decreased from 7,408 to 1,424 V/cm and from 55.0 to 24.1, respectively, with an increase in the sintering temperature. Concerning stability, the varistor ceramics sintered at 925 °C exhibited surprisingly stable accelerated aging characteristics, with %ΔE_{1 mA} = 1.4 % and %Δα = 13 % for DC accelerated aging stress of 0.85 E_{1 mA}/85 °C/24 h.     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Microstructure and dielectric properties of BaZr x Ti1−x O3 ceramics

The crystalline structure and dielectric properties of BaZr _x Ti_1−x O₃ ceramics with x = 0.05, 0.10, 0.15, and 0.20 were investigated. As zirconium increased, the a-axis lattice constant gradually increased, however, the c-axis lattice constant and c/a ratio gradually decreased. When x = 0.20, the crystal structures of the BZT ceramics are very close to cubic, different from the tetragonal structure when x < 0.20. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the increased Zr content. The decreases of coercive electric field and remanent polarization were the result of increase of Zr/Ti ratio in BaZr _x Ti_1−x O₃.     

Effects of Li2O3–B2O3–SiO2 addition on dielectric properties and microstructure of MgO–TiO2–ZnO–CaO ceramics

The effect of Li₂O₃–B₂O₃–SiO₂ (LBS) liquid-phase additives on the sintering, microstructures, and dielectric properties of MgO–TiO₂–ZnO–CaO (MTZC) ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the dielectric properties of MTZC ceramics could be greatly improved by adding a small amount of LBS solution additives. With the addition of 10 wt% LBS, the ceramics sintered at 900 °C showed favorable dielectric properties with ε_r = 21.7, Qf = 5.0 × 10⁴ GHz, and TCF = ?21.6 ppm/ °C. The distructive physical analysis showed an excellent co-firing interfacial behavior between the MTZC ceramic and the Ag electrode. It indicated that MTZC ceramics with LBS solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology.     

Preparation and characterization of the microstructure,dielectric and magnetoelectric properties of multiferroic Sr3CuNb2O9–CoFe2O4 ceramics

Different research methods were used to study the microstructural and magnetoelectric properties of multiferroic Sr₃CuNb₂O₉–CoFe₂O₄ (SCNO–CFO). X-ray verification provides fundamental information about the local symmetry of the two-phase SCNO–CFO ceramic. P4mm unit cell with minimal tetragonality and a cubic Fd-3m structure have been found for SCNO and CFO, respectively. Some additional traces of cupric oxide were also detected. SEM observations confirmed that the microstructure is built of various crystallites forming a two-component electroceramics and CuO-rich grain boundary segregation. Impedance spectroscopy studies reveal the thermally activated dielectric relaxations. The temperature-dependent behavior of the diffuse dielectric anomalies was successfully described by the modified Debye equation. Finally, magnetoelectric measurements clearly confirm intrinsic coupling between the piezoelectric and magnetic phases of SCNO–CFO.     

Microstructure and dielectric properties of sintered Li–Nb–Ti–O solid solution ceramics having superstructure

Effects of preparation conditions on the microstructures and periodicity of the superstructure for Li_1+xNb_1–xTi_xO₃ phase M polycrystals were investigated. Obtained specimens, mainly comprised of elongated plate-like grains, and their surfaces were found to be parallel to periodical domains. Sintered materials were found to contain Nb-doped Li₂TiO₃ based solid solution that was one of the end members in the phase diagram of constituent materials. Superperiodicity of phase M was found to be affected by the both chemical compositions and sintering conditions. The dielectric constant increased with increasing of periodicity of superstructures, which could be varied by the amount of Ti concentration. Electronic Publication