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1.
Pure K0.5Na0.5NbO3 lead-free piezoelectric ceramics without any dopants/additives were sintered at various temperatures (950–1125 °C) in low pO2 atmosphere (pO2?~?10?6 atm). All ceramics exhibit high relative densities (>?94%) and low weight loss (<?0.6%). Compared to the ceramics sintered in air, the ceramics sintered in low pO2 exhibit improved electrical properties. The piezoelectric constant d33 and converse piezoelectric constant d33* are 112 pC/N and 119 pm/V, respectively. The ceramics show typical ferroelectric behavior with the remnant polarization of 21.6 µC/cm2 and coercive field of 15.5 kV/cm under measurement electric field of 70 kV/cm. The good electrical properties of the present samples are related to the suppression of volatility of the alkali cations during the sintering process in low pO2 atmosphere.  相似文献   

2.
In the present work, a novel MgAl2Ti3O10 ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl2Ti3O10 phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density (ρ), relative permittivity (ε r ) and Q?×?f value firstly increased, reached the maximum values (3.61 g/cm3, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency (τ f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl2Ti3O10 ceramics exhibited the best microwave dielectric properties with Q?×?f?=?26,450 GHz, ε r ?=?14.9 and τ f ?=???83.7 ppm/°C.  相似文献   

3.
The microwave dielectric properties of Ba2MgWO6 ceramics were investigated with a view to the use of such ceramics in mobile communication. Ba2MgWO6 ceramics were prepared using the conventional solid-state method with various sintering temperatures. Dielectric constants (? r ) of 16.8–18.2 and unloaded quality factor (Q u  × f) of 7000–118,200 GHz were obtained at sintering temperatures in the range 1450–1650 °C for 2 h. A maximum apparent density of 6.76 g/cm3 was obtained for Ba2MgWO6 ceramic, sintered at 1650 °C for 2 h. A dielectric constant (? r ) of 18.4, an unloaded quality factor (Q u  × f) of 118,200 GHz, and a temperature coefficient of resonant frequency (τ f ) of ?34 ppm/°C were obtained when Ba2MgWO6 ceramics were sintered at 1650 °C for 2 h.  相似文献   

4.
The Ba3(VO4)2–x wt% Co2O3 (x?=?0.5–5) ceramics were prepared by the solid state reaction method in order to reduce the sintering temperature. The effects of the Co2O3 additions on the phase composition, microstructures, sintering characteristics and microwave dielectric properties of Ba3(VO4)2 ceramics are investigated by an X-ray diffractometer, a scanning electron microscope and a network analyzer. As a result, the Q?×?f value of 54,000 GH, the ε r of 14.6 and the τf value of +58.5 ppm/°C were obtained in the sample of the Ba3(VO4)2–3 wt% Co2O3 ceramic sintered at the temperature of 925 °C, which is capable to co-fire with electrode metal of high conductivity such as Ag (961 °C). Moreover, the Q?×?f values of the sample with Co2O3 higher than that of 3 wt% additions decreased because of the formation of Ba2V2O7 phase.  相似文献   

5.
Multiferroic properties of La-modified four-layered perovskite Bi5?x La x Fe0.5Co0.5Ti3O15 (0 ≤ x ≤ 1) ceramics were investigated, by analyzing the magnetodielectric effect, magneto-polarization response and magnetoelectric conversion. X-ray diffraction indicated the formation of pure Aurivillius ceramics, and Raman spectroscopy revealed the Bi ions displacement and the crystal structure variation. The enhancement of ferromagnetic and ferroelectric properties was observed in Bi5?x La x Fe0.5Co0.5Ti3O15 after La modification. The evidence for enhanced ME coupling was determined by magnetic field-induced marked variations in the dielectric constant and polarization. A maximum ME coefficient of 1.15 mV/cm·Oe was achieved in Bi4.25La0.75Fe0.5Co0.5Ti3O15 ceramic, which provides the possible promise for novel magnetoelectric device application.  相似文献   

6.
The Bi1?+?xFe0.95Cr0.05O3 (BFCO) (x?=?0, 5, 10, 15 and 20%) thin films are fabricated on FTO/glass substrate using a chemical solution deposition method and sequential-layer annealing process. The effects of the excess Bi content on crystalline structure, morphology, and electrical performance of BFCO thin films are investigated. All the BFCO thin films are crystallized into polycrystalline perovskite structure and belonging to the space group of R3c. The BFCO thin films with 5 and 10% excess Bi contents possess no impurity phase. Especially, a dense surface morphology and columnar crystal structure can be obtained for the film with 5% excess Bi content. Especially, the one possesses superior ferroelectricity with a relative high remnant polarization (P r) of 69.8 µC/cm2 and low coercive electric field (E c) of 291 kV/cm at 1 kHz due to the relatively low leakage current density of 3.04?×?10??5 A/cm2 at 200 kV/cm.  相似文献   

7.
In this work, (Ba0.96Ca0.04)(Ti0.92Sn0.08)O3xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d 33 ~ 475 pC/N, k p ~ 50 %, ε r ~ 4060, tanδ ~ 0.4 %, P r ~ 10.3 μC/cm2, E c ~ 1.35 kV/mm, T C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO3-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.  相似文献   

8.
In the present study the effect of Zn substitution on densification, microstructure, microwave and broad band dielectric properties of MgTiO3 ceramics were investigated. The (Mg1?x Zn x )TiO3 (x?=?0.01–0.07) ceramics have been prepared by the conventional solid-state reaction method. The sintering conditions were optimized to obtain the best dielectric properties with maximum relative densities. The microwave dielectric properties are heavily influenced by the amount of x concentration. The optimum dielectric properties of ε r ~ 17.34, Q?×?f o ~ 274 THz, τ f ~ -40.3 ppm/oC is obtained for (Mg0.95Zn0.05)TiO3 ceramics sintered at 1275?°C. The broad band dielectric properties of (Mg0.95Zn0.05)TiO3 ceramics were measured in the frequency range of 1–100 MHz, and temperature range of 133–483 K. Interestingly, the broad band dielectric properties show relaxation behaviour with frequency. The higher temperature dielectric spectrum of (Mg0.95Zn0.05)TiO3 (MZT) ceramics displayed a distinct dispersion, which is shifting towards a lower frequency side. The observed dielectric relaxation behavior is analyzed using Cole–Cole plot. Furthermore, voltage dependent capacitance behavior at different frequencies is studied for the MZT sample, and it’s interesting to note that the capacitance is stable with the variation in voltage. The electrical conductivity study is carried out as a function of frequency and temperature for MZT sample and the activation energy is calculated by using Arrhenius equation, which is found to be 0.07 eV at 10 MHz. The obtained dielectric response of MZT ceramics are suitable for dielectric resonator and type-1 RF capacitor applications.  相似文献   

9.
Crystal structure and dielectric properties of Zn3Mo2O9 ceramics prepared through a conventional solid-state reaction method were characterized. XRD and Raman analysis revealed that the Zn3Mo2O9 crystallized in a monoclinic crystal structure and reminded stable up to1020 °C. Dense ceramics with high relative density (~ 92.3%) were obtained when sintered at 1000 °C and possessed good microwave dielectric properties with a relative permittivity (ε r ) of 8.7, a quality factor (Q?×?f) of 23,400 GHz, and a negative temperature coefficient of resonance frequency (τ f ) of around ??79 ppm/°C. With 5 wt% B2O3 addition, the sintering temperature of Zn3Mo2O9 ceramic was successfully lowered to 900 °C and microwave dielectric properties with ε r ?=?11.8, Q?×?f?=?20,000 GHz, and τ f = ??79.5 ppm/°C were achieved.  相似文献   

10.
In this work, the nominal CaCu3?xMgxTi4.2O12 (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ~?1.1?×?104–1.8?×?104 with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg2+ dopants due to the increase of grain boundary resistance (Rgb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg2+ dopants in the structure. In addition, CaCu3?xMgxTi4.2O12 ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (Eb) due to Mg2+doping. The high values of ε′ (14012), α (13.64) and Eb (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu2.90Mg0.10Ti4.2O12 ceramic sintered at 1100 °C for 8 h.  相似文献   

11.
Monoclinic structured Mg1?xNixZrNb2O8 (0?≤?x?≤?0.12) ceramics were synthesized for the first time through traditional solid-state reaction process and pure phase were obtained in all range. Rietveld refinement was used to analyze the crystal structure. With the increase of Ni2+ substitution amount, ε r decreased, Q?×?f rose first then fell, τ f shifted for the positive direction. Bond ionicity, lattice energy and bond energy were separately calculated to investigate the correlations with microwave dielectric properties. Typically, ceramics samples with the composition of Mg0.92Ni0.08ZrNb2O8 sintered at 1280 °C for 4 h exhibited the optimum microwave dielectric properties: ε r ?=?24.58, Q?×?f?=?74534.1 GHz, τ f ?=???49.11 ppm/°C, which could be a promising material for application.  相似文献   

12.
Li6Mg7Ti3O16 ceramics were prepared by the conventional solid-state method with 1–5 wt% LiF as the sintering aid. Effects of LiF additions on the phase compositions, sintering characteristics, micro-structures and microwave dielectric properties of Li6Mg7Ti3O16 ceramics were investigated. The LiF addition could effectively lower the sintering temperature of Li6Mg7Ti3O16 ceramics from 1550 to 900 °C. For different LiF-doped compositions, the optimum dielectric permittivity (ε r ) and quality factor (Q·f) values first increased and then decreased with the increase of LiF contents, whereas the temperature coefficient of resonant frequency (τ f ) fluctuated between ??14.39 and ??8.21 ppm/°C. Typically, Li6Mg7Ti3O16 ceramics with 4 wt% LiF sintered at 900 °C exhibited excellent microwave dielectric properties of ε r ?=?16.17, Q·f?=?80,921 GHz and τ f ?=???8.21 ppm/°C, which are promising materials for the low temperature co-fired ceramics applications.  相似文献   

13.
Novel green-emitting piezoelectric ceramics of SrBi4?x Er x Ti4O15 (SBT-xEr) were prepared. Strong up-conversion with bright green (524 and 548 nm) and a relatively weak red (660 nm) emission bands were obtained under 980 nm excitation at room temperature, which is attributed to the intra 4f–4f electronic transition of (2H11/2, 4S3/2)–4I15/2 and the transition from 4F9/2 to 4I15/2 of Er3+ ions, respectively. Simultaneously, Er3+ doping promotes the electrical properties. At 0.8 mol%Er, the optimal electric properties with high Curie temperature of T c?~527?°C, large remanent polarization of 2P r?~14.92 μC/cm2 and piezoelectric constant of d 33?~17 pC/N was achieved. As a multifunctional material, Er3+ doped SBT showed a great potential to be used in 3D-display, bio-imaging, solid state laser and optical temperature sensor.  相似文献   

14.
Sr1?x Nd x TiO3 (x?=?0.08–0.14) ceramics were prepared by conventional solid-state methods. The analysis of crystal structure suggested Sr1?x Nd x TiO3 ceramics appeared to form tetragonal perovskite structure. The relationship between charge compensation mechanism, microstructure feature and microwave dielectric properties were investigated. Trivalent Nd3+ substituting Sr2+ could effectively decrease oxygen vacancies. This reduction and relative density were critical to improve Q?×?f values of Sr1?x Nd x TiO3 ceramics. For ε r values, incorporation of Nd could restrain the rattling of Ti4+ cations and led to the reduction of dielectric constant. The τ f values were strongly influenced by tilting of oxygen octahedral. The τ f values decreased from 883 to 650 ppm/°C with x increasing from 0.08 to 0.14. A better microwave dielectric property was achieved for composition Sr0.92Nd0.08TiO3 at 1460 °C: ε r ?=?160, Q?×?f?=?6602 GHz, τ f ?=?883 ppm/°C.  相似文献   

15.
Solution-based chemical method has been used to produce LiCo3/5Mn1/5Cu1/5VO4 ceramics. The formation of the compound is checked by X-ray diffraction analysis and it reveals an orthorhombic unit cell structure with lattice parameters of a = 9.8262 Å, b = 3.0706 Å, c = 14.0789 Å. Field emission scanning electron micrograph indicates a polycrystalline texture of the material with grains of unequal sizes (~0.2 to 3 μm). Complex impedance spectroscopy technique is used to study the dielectric properties. Temperature dependence of dielectric constant (ε r) at various frequencies exhibits the dielectric anomalies in ε r at T c (transition temperature) = 245, 255, 260 and 265 °C with (εr)max. ~458, 311, 214 and 139 for 50, 100, 200 and 500 kHz, respectively. Frequency dependence of tangent loss at various temperatures shows the presence of dielectric relaxation in the material.  相似文献   

16.
Li2Mg3SnO6 (abbreviation for LMS) ceramics doped with 1–4 wt% lithium fluoride (LiF) were prepared by the conventional solid-state reaction method. The effects of LiF addition on the phase compositions, sintering behaviors and microwave dielectric properties of LMS ceramics were investigated. A small amount of LiF addition could effectively decrease the sintering temperatures due to the liquid phase in the sintering process and induced no apparent degradation of the microwave dielectric properties. The optimized quality factor values for each composition firstly increased and then decreased with the increase of the LiF content. Whereas, the optimized dielectric permittivity increased with increasing of the LiF content. Distinguished microwave dielectric properties with a dielectric constant (ε r) of 11.13, a quality factor (Q·f) of 104,750 GHz, and a temperature coefficient of resonant frequency (τ f ) of ?10.83 ppm/°C were obtained for LMS ceramics sintered at 950?°C doped with 3 wt% LiF, which showed that the materials were suitable for the low temperature co-fired ceramics applications (LTCC).  相似文献   

17.
Na0.65Bi0.45Cu3Ti4O12 ceramics were successful prepared by the conventional solid-state reaction technique. Compared to Na0.50Bi0.50Cu3Ti4O12 (NBCTO), the composition of Na0.65Bi0.45Cu3Ti4O12 was designed in terms of changing the Na/Bi ratio. Colossal dielectric permittivity of ~1.2 × 104 at 1 kHz was obtained in Na0.65Bi0.45Cu3Ti4O12 ceramics. Interestingly, three frequency dispersions were observed in the frequency dependence of dielectric constant measured at different temperatures. The investigation of electric modulus displayed that the giant low-frequency dielectric constant was attributed to Maxwell–Wagner polarization at the grain boundaries and the frequency dispersion in middle-frequency range was due to the grain polarization. Except grain response and grain boundaries response reflected by two semicircles in the impedance spectroscopy, another electrical response associated with nonzero high frequency intercept was found. The grain resistance Rg and grain boundaries resistance R gb was ~600 Ω and 3.9 × 105 Ω, respectively. The large intrinsic permittivity as high as ~700 was obtained. Furthermore, two dielectric anomalies observed in the temperature dependent of dielectric constant were discussed in detail. The results indicated change in the Na/Bi ratio had a significant effect on the electrical properties of NBCTO ceramics.  相似文献   

18.
High aspect ratio patelike NaNbO3 particles with pure perovskite structure have been successfully synthesized by topochemical microcrystal conversion (TMC) from plate-like precursor particles of the layer-structured Bi2.5Na3.5Nb5O18. By changing the Bi2.5Na3.5Nb5O18/Na2CO3 ratio, large and thin NaNbO3 particles with a thickness of approximately 0.5 μm and a width of approximately 20 μm were obtained. The obtained NaNbO3 particles is quite suitable for fabricating textured (K0.5Na0.5)NbO3-based ceramics. Using the fine platelike NaNbO3 particles as templates, dense <001> -oriented (K0.5Na0.5)NbO3-0.5 mol %MnO2 ceramics with high texture quality (Lotgering factor F 001 = 87 %) and excellent piezoelectric properties were produced by templated grain growth. Compared with randomly oriented ceramics, textured samples show greatly enhanced properties. The room-temperature strain S, the piezoelectric coefficient d 33 * and d 33 reach up to 0.093 %, 233 pm/V and 195pC/N, respectively, which are all about 1.5 times larger than those of non-textured ceramics.  相似文献   

19.
The modulus Spectroscopy of Lead Potassium Titanium Niobate (Pb0.95K0.1Ti0.25Nb1.8O6, PKTN) Ceramics was investigated in the frequency range from 45 Hz to 5 MHz and the temperature, from 30 to 600 °C. XRD analysis in PKTN indicated a orthorhombic structure with lattice parameters a = 18.0809 Å, b = 18.1909 Å and c = 3.6002 Å. The dielectric anomaly with a peak was observed at 510 °C. Variation of εI and εII with frequency at different temperatures exhibit high values, which reflects the effect of space charge polarization and/or conduction ion motion. The electrical relaxation in ionically conducting PKTN ceramic analyzed in terms of Impedance and Modulus formalism. The Cole–Cole plots of impedance were drawn at different temperatures. The dielectric modulus, which describes the dielectric relaxation behaviour is fitted to the Kohlrausch exponential function. Near the phase transition temperature, a stretched exponential parameter β indicating the degree of distribution of the relaxation time has a small value. From the AC conductivity measurements the activation energy near phase transition temperature (T C°C) has been found to different from that of the above and below T C. The temperature dependence of electrical modulus has been studied and results are discussed.  相似文献   

20.
(Ba0.67Sr0.33)1?3x/2Y x Ti1?y/2Mn y O3 [BST(Mn + Y), x = 0.006, y = 0.005] ceramics were fabricated by using citrate–nitrate combustion derived powder. Microstructure and dielectric properties of the BST(Mn + Y) ceramic samples were investigated within the sintering temperature ranged from 1220 to 1300 °C. Sintering temperature has a great influence on the microstructure and electrical properties of the ceramic samples. The dielectric properties, ferroelectric properties, and tunability are enhanced by optimizing sintering temperature. The relatively high tunability of 40 % (1.5 kV/mm DC field, 10 kHz) was obtained, and relatively low dielectric loss, <0.0052 (at 10 kHz, 20 °C) was acquired for BST(Mn + Y) samples sintered at 1275 °C for 3 h. Both the low dielectric loss and enhanced tunable properties of BST(Mn + Y) are useful for tunable devices application.  相似文献   

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