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1.
The xBi(Zn2/3Nb1/3)O3–(1?x)(K0.5Na0.5)NbO3 (abbreviated as xBZN–(1?x)KNN) ceramics have been synthesized using the conventional solid‐state sintering method. The phase structure, dielectric properties and “relaxorlike” behavior of the ceramics were investigated. The 0.03BZN–0.97KNN ceramics show a broad and stable permittivity maximum near 2000 and lower dielectric loss (≤5%) at a broad temperature usage range (100°C–400°C) and the capacitance variation (ΔC/C150°C) is maintained smaller than ±15%. The 0.03BZN–0.97KNN ceramics only possess the diffuse phase transition and no frequency dispersion of dielectric permittivity, which indicates that 0.03BZN–0.97KNN ceramics is a high temperature “relaxorlike” ferroelectric ceramics. These results indicate that 0.03BZN–0.97KNN ceramics are excellent promising candidates for preparing high‐temperature multilayer ceramics capacitors.  相似文献   

2.
In this study, we have investigated the use of silver cation as nucleating agent in germanotellurite glass matrix of compositions (100?x) [70TeO2–10GeO2–10Nb2O5–10K2O]–xAg2O (x=0‐6 mol%), in order to promote bulk crystallization. Density measurements, differential scanning calorimetry, X‐ray diffraction, UV‐Vis, and Raman spectroscopies have been performed to study the crystallization process. We have observed bulk crystallization of a unique noncentrosymmetric phase, K[Nb1/3Te2/3]2O4.8, which has been investigated for its second‐order optical activity. Transparent to translucent glass‐ceramics have been successfully tailored under thermal treatment and second harmonic generation signals were recorded on the glass‐ceramic samples as a function of their synthesis procedure. It is suggested that the second‐order optical properties observed are strongly related to the organization of crystallites within phase‐separated domains.  相似文献   

3.
A series of temperature‐stable microwave dielectric ceramics, (1?x)(Na0.5La0.5)MoO4x(Na0.5Bi0.5)MoO4 (0.0 ≤ x ≤ 1.0) were prepared by using solid‐state reaction. All specimens can be well sintered at temperature of 580°C–680°C. Sintering behavior, phase composition, microstructures, and microwave dielectric properties of the ceramics were investigated. X‐ray diffraction results indicated that tetragonal scheelite solid solution was formed. Microwave dielectric properties showed that permittivity (εr) and temperature coefficient of resonant frequency (τf) were increased gradually, while quality factor (Q × f) values were decreased, at the x value was increased. The 0.45(Na0.5La0.5)MoO4–0.55(Na0.5Bi0.5)MoO4 ceramic sintered at 640°C with a relative permittivity of 23.1, a Q × f values of 17 500 GHz (at 9 GHz) and a near zero τf value of 0.28 ppm/°C. Far‐infrared spectra (50–1000 cm?1) study showed that complex dielectric spectra were in good agreement with the measured microwave permittivity and dielectric losses.  相似文献   

4.
Al/Nb co‐doped SrTiO3 microwave ceramics with the composition of SrTi1–x(Al0.5Nb0.5)xO3 (x = 0.03, 0.05, 0.1, and 0.15) have been synthesized via a standard solid‐state reaction method. The substitution of (Al0.5Nb0.5)4+ in B‐site inhibits the reduction in Ti4+ ions and the growth of grain size, then the transport of mobile charge carriers is limited, and thus the Q value is improved. For the SrTi0.9(Al0.5Nb0.5)0.1O3 ceramics, in addition to their high dielectric constant (εr ~185), they exhibit correspondingly a high Qf value (~ 9077 GHz) at 2.9 GHz, making the microwave ceramics suitable for myriad device miniaturization and high‐performance wireless communication.  相似文献   

5.
The structure, microwave dielectric properties, and low‐temperature sintering behavior of acceptor/donor codoped Li2TiO3 ceramics [Li2Ti1?x(Al0.5Nb0.5)xO3, x = 0–0.3] were investigated systematically. The x‐ray diffraction confirmed that a single‐phase solid solution remained within 0 < x ≤ 0.2 and secondary phases started to appear as x > 0.2, accompanied by an order–disorder phase transition in the whole range. Scanning electron microscopy observation indicated that the complex substitution of Al3+ and Nb5+ produced a significant effect on the microstructural morphology. Both microcrack healing and grain growth contributed to the obviously enhanced Q×f values. By comparison, the decrease of εr and τf values was ascribed to the ionic polarizability and the cell volume, respectively. Excellent microwave dielectric properties of εr ~ 21.2, Q×f ~ 181 800 GHz and τf  ~ 12.8 ppm/°C were achieved in the x = 0.15 sample when sintered at 1150°C. After 1.5 mol% BaCu(B2O5) additive was introduced, it could be well sintered at 950°C and exhibited good microwave dielectric properties of εr ~ 20.4, Q×f ~ 53 290 GHz and τf ~ 3.6 ppm/°C as well. The cofiring test of the low‐sintering sample with Ag powder proved its good chemical stability during high temperature, which enables it to be a promising middle‐permittivity candidate material for the applications of low‐temperature cofired ceramics.  相似文献   

6.
Colossal permittivity (CP) (εr=104~105) is attained in (A1/3Nb2/3)xTi1xO2 (A=Ba2+, Ca2+, Zn2+, Mg2+) ceramics. Here, (Ca1/3Nb2/3)xTi1xO2 material was studied as a typical example, and effects of Ca and Nb on their microstructure, dielectric properties and stability were studied. Both backscattering and elements mapping strongly confirmed the formation of secondary phases due to the addition of Ca and/or Nb. Secondary phases‐induced by Ca cannot affect dielectric properties of the ceramics when low Ca and Nb contents were doped, while secondary phases formed by Ca and Nb strongly affected their dielectric properties in a high doping level. In particular, their dielectric properties can be well modified by the optimization of sintering temperatures. In addition, the (Ca1/3Nb2/3)xTi1xO2 ceramics with x=0.01 exhibited the optimum dielectric properties (εr=130500 and tan δ=0.19). Electron‐pinned defect‐dipoles may be suitable to explain CP phenomenon of this work. We believed that this profound investigation can benefit the development of new TiO2 ceramics as a CP material.  相似文献   

7.
x(NaF?0.5Nb2O5)?(1 ? x)[(Na0.5K0.5)(Nb0.8Ta0.2)O3] (100xNN?NKNT) piezoelectric ceramics were fabricated to high densities above 97% when sintering at temperatures ~1200°C. Compared with pure (Na,K)NbO3 (NKN), dielectric constants of the NaF–Nb2O5 flux‐doped NKNT ceramics were increased whereas dielectric losses remained low. High field polarization switching showed very square hysteresis loops, but the coercive fields were decreased through a “softening” doping effect induced by the flux. A Rayleigh analysis inferred that the extrinsic contribution from the domain wall dynamics was increased with the flux addition. Collectively, all the experimental observations suggested that NaF–Nb2O5 was, in part, soluble in the structure and highly suitable for obtaining a stable NKN system with improved piezoelectric performance.  相似文献   

8.
(1?x)Pb(Hf1?yTiy)O3xPb(Yb0.5Nb0.5)O3 (= 0.10–0.44, = 0.55–0.80) ceramics were fabricated. The morphotropic phase boundary (MPB) of the ternary system was determined by X‐ray powder diffraction. The optimum dielectric and piezoelectric properties were achieved in 0.8Pb(Hf0.4Ti0.6)O3–0.2Pb(Yb0.5Nb0.5)O3 ceramics with MPB composition, where the dielectric permittivity εr, piezoelectric coefficient d33, planar electromechanical coupling kp, and Curie temperature Tc were found to be on the order of 1930,480 pC/N, 62%, and 360°C, respectively. The unipolar strain behavior was evaluated as a function of applied electric field up to 50 kV/cm to investigate the strain nonlinearity and domain wall motion under large drive field, where the high field piezoelectric d33* was found to be 620 pm/V for 0.82Pb(Hf0.4Ti0.6)O3–0.18Pb(Yb0.5Nb0.5)O3. In addition, Rayleigh analysis was carried out to study the extrinsic contribution, where the value was found to be in the range 2%–18%.  相似文献   

9.
Multilayer pulsed power ceramic capacitors require that dielectric ceramics possess not only large recoverable energy storage density (Wrec) but also low sintering temperature (<950°C) for using the inexpensive metals as the electrodes. However, lead‐free bulk ceramics usually show low Wrec (<2 J/cm3) and high sintering temperature (>1150°C), limiting their applications in multilayer pulsed power ceramic capacitors. In this work, large Wrec (~4.02 J/cm3 at 400 kV/cm) and low sintering temperature (940°C) are simultaneously achieved in 0.9(K0.5Na0.5)NbO3–0.1Bi(Mg2/3Nb1/3)O3–1.0 mol% CuO ceramics prepared using transition liquid phase sintering. Wrec of 4.02 J/cm3 is 2‐3 times as large as the reported value of other (Bi0.5Na0.5)TiO3 and BaTiO3‐based lead‐free bulk ceramics. The results reveal that 0.9(K0.5Na0.5)NbO3–0.1Bi(Mg2/3Nb1/3)O3–1.0 mol% CuO ceramics are promising candidates for fabricating multilayer pulsed power ceramic capacitors.  相似文献   

10.
0.94(Na0.5Bi0.5+x)TiO3–0.06BaTiO3 (x = ?0.04, 0, 0.02; named NB0.46T‐6BT, NB0.50T‐6BT, NB0.52T‐6BT, respectively) lead‐free piezoelectric ceramics were prepared via the solid‐state reaction method. Effects of Bi3+ nonstoichiometry on microstructure, dielectric, ferroelectric, and piezoelectric properties were studied. All ceramics show typical X‐ray diffraction peaks of ABO3 perovskite structure. The lattice parameters increase with the increase in the Bi3+ content. The electron probe microanalysis demonstrates that the excess Bi2O3 in the starting composition can compensate the Bi2O3 loss induced during sample processing. The size and shape of grains are closely related to the Bi3+ content. For the unpoled NB0.50T‐6BT and NB0.52T‐6BT, there are two dielectric anomalies in the dielectric constant–temperature curves. The unpoled NB0.46T‐6BT shows one dielectric anomaly accompanied by high dielectric constant and dielectric loss at low frequencies. After poling, a new dielectric anomaly appears around depolarization temperature (Td) for all ceramics and the Td values increase with the Bi3+ amount decreasing from excess to deficiency. The diffuse phase transition character was studied via the Curie–Weiss law and modified Curie–Weiss law. The activation energy values obtained via the impedance analysis are 0.69, 1.05, and 1.16 eV for NB0.46T‐6BT, NB0.50T‐6BT and NB0.52T‐6BT, respectively, implying the change in oxygen vacancy concentration in the ceramics. The piezoelectric constant, polarization, and coercive field of the ceramics change with the variation in the Bi3+ content. The Rayleigh analysis suggests that the change in electrical properties of the ceramics with the variation in the Bi3+ amount is related to the effect of oxygen vacancies.  相似文献   

11.
New lead‐free piezoelectric ceramics of 0.9BaTiO3–(0.1?x)(Bi0.5Na0.5)TiO3xBiMO3, M=Al and Ga, where x=0.00‐0.10, were fabricated by the solid‐state reaction technique. The effect of BiMO3 contents on the perovskite structure, phase transition, and dielectric, ferroelectric, and piezoelectric properties was investigated. X‐ray diffraction patterns showed that the ceramics exhibit a monophasic perovskite phase up to x=0.06, suggesting stabilized perovskite structures with B‐site aliovalent substitutions. Compositional‐dependent phase transitions were observed from tetragonal to pseudo‐cubic phase with increasing BiMO3 amounts. Al3+ ions were found to stabilize the transition temperature of the ceramics, while significantly decreasing transition temperature, and a change in the dielectric peak were found with an increasing amount of Ga3+. Regarding Al3+ substitution, the remanent polarization (Pr) values were found to decrease slightly with the Al3+ amount. With regard to Ga3+ substitution, Pr values decreased with the Ga3+ amount up to 0.06 and then increased slightly. The ceramics became softer with a higher degree of substitution according to the lower coercive field (Ec), when compared with 0.9BaTiO3–0.1(Bi0.5Na0.5)TiO3 ceramics. Ceramics with a lower degree of substitution and tetragonal phase showed butterfly strain loops that correlated with normal ferroelectric behavior.  相似文献   

12.
In this work, new glass compositions were prepared in the ternary system GeO2–K2O–Ta2O5. Potassium oxide was added to reach the complete melt of the starting mixture and two composition series were investigated: the first one with a constant K2O molar content of 10% in the ternary system (90–x)GeO2–10K2O–xTa2O5 and the second one with the same molar content of K2O and Ta2O5 in the ternary system (100–2x)GeO2xK2O–xTa2O5. Homogeneous and transparent glasses could be obtained between x = 0 and 20. X‐ray diffraction analyzes of samples with x = 25 identified orthorhombic Ta2O5 in the first series and an isostructure of K3.8Ge3Nb5O20.4 in the second series where it is assumed that Ta5+ ions are inserted in the Nb5+ sites. As one of our goal with these materials is related with the preparation of glass‐ceramics containing Ta2O5 nanocrystals, the first series has been selected for further characterizations. An increase in glass‐transition temperatures with increasing Ta2O5 content as well as an increase of the thermal stability from x = 0 to 10 has been identified by differential scanning calorimetry. For higher contents, crystallization events were identified. Fourier transform infrared and Raman spectroscopic characterizations allowed to point out the intermediary behavior of Ta2O5 in the vitreous network where TaO6 octahedra are inserted inside the germanate network with TaO6 clusters identified at higher Ta2O5 contents. Heat‐treated samples with high tantalum contents (x = 15 and 20) exhibit preferential precipitation of orthorhombic Ta2O5 with nanometric size, suggesting the possibility of obtaining transparent glass‐ceramics for optical applications.  相似文献   

13.
Solid solutions of (1?x)BaTiO3xBi(Mg2/3Nb1/3)O3 (0 ≤ x ≤ 0.6) were prepared via a standard mixed‐oxide solid‐state sintering route and investigated for potential use in high‐temperature capacitor applications. Samples with 0.4 ≤ x ≤ 0.6 showed a temperature independent plateau in permittivity (εr). Optimum properties were obtained for x = 0.5 which exhibited a broad and stable relative εr ~940 ± 15% from ~25°C to 550°C with a loss tangent <0.025 from 74°C to 455°C. The resistivity of samples increased with increasing Bi(Mg2/3Nb1/3)O3 concentration. The activation energies of the bulk were observed to increase from 1.18 to 2.25 eV with an increase in x from 0 to 0.6. These ceramics exhibited excellent temperature stable dielectric properties and are promising candidates for high‐temperature multilayer ceramic capacitors for automotive applications.  相似文献   

14.
Highly transparent lead‐free (1‐x)K0.5Na0.5NbO3xSr(Zn1/3Nb2/3)O3 (KNN–xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically clear, showing high transmittance in the visible and near‐infrared regions (~70% and ~80% at 0.5 mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo‐cubic phase structure as well as the dense and fine‐grained microstructure. In addition, a high energy storage density of 3.0 J/cm3 has been achieved for the 0.94K0.5Na0.5NbO3–0.06Sr(Zn1/3Nb2/3)O3 ceramics with submicron‐sized grains (~136 nm). The main reason is likely to be the typical relaxor‐like behavior characterized by diffuse phase transition, in addition to the dense and fine‐grained microstructure. This study demonstrates that the 0.94K0.5Na0.5NbO3–0.06Sr(Zn1/3Nb2/3)O3 ceramic is a promising candidate of lead‐free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications.  相似文献   

15.
Dielectric and piezoelectric properties of CuO‐added KNbO3 (KN) ceramics were investigated. The CuO reacted with the Nb2O5, formed a CuO–Nb2O5‐related liquid phase during the sintering, and assisted the densification of the KN ceramics at low temperatures. Moreover, some of the Cu2+ ions replaced the Nb5+ ions in the matrix and behaved as a hardener. The dielectric and piezoelectric properties of the KN ceramics were considerably influenced by the relative density. The 1.0 mol% CuO‐added KN ceramic sintered at 960°C for 1.0 h, which showed a maximum relative density, exhibited a high phase angle of 86.9°, Pr of 14.8 μC/cm2, and Ec of 1.8 kV/mm. This specimen also exhibited good dielectric and piezoelectric properties: εT33/εo of 364, d33 of 122 pC/N, kp of 0.29, and Qm of 611.  相似文献   

16.
The structure and electrical properties of perovskite layer structured (PLS) (1?x)Sr2Nb2O7x(Na0.5Bi0.5)TiO3 (SNO‐NBT) prepared by solid‐state reaction method are investigated. The addition of NBT is beneficial to speed up mass transfer and particle rearrangement during sintering, leading to better sinterability and higher bulk density up to 96.8%. The solid solution limit x in the SNO‐NBT system is below 0.03, over which Ti4+ is preferable to aggregate and results in the generation of secondary phase. After the modification by NBT, all SNO‐NBT ceramics have a Curie temperature Tc up to over 1300°C and piezoelectric constant d33 about 1.0 pC/N. The breakthrough of piezoelectricity can mainly be attributed to rotation and distortion of oxygen octahedron as well as higher poling electric field resulting from the improved bulk density. This study not only demonstrates how to improve piezoelectricity by NBT addition, but also opens up a new direction to design PLS piezoceramics by introducing appropriate second phase.  相似文献   

17.
A series of textured (Nb0.5La0.5)xTi1-xO2 (x = 0, 0.0025, 0.005, 0.01) ceramics were sintered in a nitrogen environment after magnetic slip casting (12 T). Component x ranges from 0.0025 to 0.01 while the degree of orientation increases from 0.49 to 0.88. (Nb0.5La0.5)0.01Ti0.99O2 ceramics in the parallel magnetic field's plane have a high permittivity ɛr ≈ 1.6 × 104 and the ultralow dielectric loss tanδ ≈ 0.0038 at 104 Hz. The temperature coefficient value of η ≤ ± 7.1% between 218–473 K, fulfilling the X9R requirements. The giant permittivity properties of textured ceramics are mainly derived from internal barrier layer capacitor impacts, electron hopping, and electron-pinned defect-dipoles polarization. The microstructure evolution of sintered ceramics was modified by texturing in a magnetic field, leading to higher activation energies of dielectric relaxations and resistance of grain boundaries and grains. This excellent performance is expected to show great potential in electronic devices' miniaturization and high-density energy storage.  相似文献   

18.
Zinc borate glasses with different concentrations of Nb2O5 were prepared and later were heat treated for prolonged times. Prepared samples were characterized by XRD, SEM, DSC, IR and optical transmission spectroscopy techniques. Later, dielectric properties viz., dielectric constant, loss tangent, electric modulii, electrical impedance and a.c. conductivity over wide ranges of frequency and temperature, were investigated as a function of Nb2O5 concentration. Finally, the dielectric breakdown strength was measured in air medium at ambient temperature. The results of characterization techniques viz., XRD, SEM and DSC indicated that multiple crystal grains (with sizes varying from 0.1 to 1 μm) are dispersed in the residual glass phase. The concentration of crystal grains found to increase with increase in Nb2O5 content. The XRD studies have further revealed that the bulk samples are composed of columbite ZnNb2O6 crystal phases. Using generalized gradient approximation (GGA) quantitative information on these crystal phases viz., the lattice parameters, optical band gap and band structure were evaluated. The analysis of results of IR spectral studies have indicated that there is an increasing degree of polymerization of glass network with increase in Nb2O5 content due to the increased connectivity between various structural groups in the glass network. The optical absorption spectra indicated an increase in optical transmittance of the bulk samples with increase in Nb2O5 content. The dielectric parameters are observed to decrease, whereas the dielectric breakdown strength is observed to increase to a large extent due to the crystallization of the glass with the Nb2O5. The increase is attributed to the formation of ZnNb2O6 crystalline phases that contain intertwined ZnO6 and NbO6 structural units. As a whole, zinc borate glasses exhibited a significant increase in the electrical insulating strength due to the crystallization with Nb2O5 as the crystallizing agent. Further, the value of dielectric constant is also found to be the optimal with no dispersion with frequency up to 450 K. Overall, the studied glass‐ceramics meet the necessary physical conditions to be used as insulating layers in the display panels and hence may be considered for such applications.  相似文献   

19.
Evolution of crystal structure in Pb1‐xBax(Fe1/2Nb1/2)O3 ceramics has been investigated by X‐ray diffraction and Raman spectra analysis together with the dielectric characterization. The crystal structure for all compositions is cubic and the cell volume indicates a sudden change at = 0.075. Pb1‐xBax(Fe1/2Nb1/2)O3 ceramics with > 0.075 are paraelectric, whereas those for < 0.075 are ferroelectric at room temperature. The evolution of phonon modes indicates that the ferroelectricity of Pb1‐xBax(Fe1/2Nb1/2)O3 solid solution ceramics is caused by the off‐center Nb5+ in BO6 octahedron. The ferroelectric‐related distortion is still observed in paraelectric solid solutions with > 0.075.  相似文献   

20.
(1 ? x)Ba0.6Sr0.4La4Ti4O15xBa5Nb4O15 (x = 0.05, 0.1, 0.15 and 0.2, BSLT–BN) ceramic samples were prepared by co‐firing the mixtures of Ba0.6Sr0.4La4Ti4O15 and Ba5Nb4O15 powders. Crystal structure, microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of the BSLT–BN series ceramics were investigated. X‐ray diffraction patterns reveal that all the samples exhibit a hexagonal perovskite structure, which implies that the BSLT–BN mixtures form solid solutions. With increasing Ba5Nb4O15 content, the diffraction peaks shift to low angles and the sintering temperature of BSLT–BN decreases. Raman spectra analysis reveals the shifting and splitting of the vibration modes. The microwave dielectric properties of the well‐sintered (1 ? x)BSLT–xBN ceramics vary with Ba5Nb4O15 content. The dielectric permittivity of the ceramics exhibits a slight decreasing trend. The quality factor varies in the range of 45 000–11 200 GHz, whereas near‐zero temperature coefficients of the resonant frequency may be achieved by changing the Ba5Nb4O15 content. TSDC was utilized to explore the extrinsic loss mechanism associated with defects. TSDC relaxation peaks are mainly generated by oxygen vacancies, and the Ba5Nb4O15 content has a significant influence on the TSDC spectra.  相似文献   

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