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1.
Min-Han KimChang-Soo Woo Sahn Nahm Chang-Hack ChoiHwack-Joo Lee Hyun-Min Park 《Materials Research Bulletin》2002,37(3):605-615
Crystal structure and microwave dielectric properties of (1−x)NdAlO3-xCaTiO3 ceramics have been investigated. Crystal structure of the specimens changed with the composition. Rhombohedral structure was found for the specimens with x≤0.1. When 0.3≤x≤0.7, the specimens had the tetragonal structure and it changed to the orthorhombic structure as x exceeded 0.7. Two types of the second phases were observed in (1−x)NdAlO3-xCaTiO3 ceramics. For the specimens with x≤0.5, Nd4Al2O9 phase was observed and Al-rich phase was found in the specimens with x≥0.7. The dielectric constant (εr) and the temperature coefficient of the resonant frequency (τf) increased with the increase of x. The Q×f value of the specimen increased with x and exhibited the maximum value when x=0.5. The microwave dielectric properties of Q×f=45,000 GHz, εr=45 and τf=−1.5 ppm/°C were obtained for 0.3NdAlO3-0.7CaTiO3 ceramics. 相似文献
2.
Jung-A Lee 《Materials Research Bulletin》2005,40(10):1839-1846
Pb(Zn1/3Ta2/3)O3 ceramics, compositionally modified by the incorporation of Fe to the octahedral lattice sites, were prepared and characterized in terms of perovskite development, dielectric properties, as well as microstructure evolution. The powders of the B-site precursor compositions were synthesized separately and reacted with PbO to form Pb[(Zn1/3Ta2/3),(Fe1/2Ta1/2)]O3. The perovskite contents increased continuously with the Fe concentration. The maximum dielectric constant values of the ceramics increased tremendously with the fraction of Fe, whereas the dielectric maximum temperatures were rather insensitive to the compositional change. 相似文献
3.
(5 − x)BaO-xMgO-2Nb2O5 (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO3, MgO, and Nb2O5 was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 °C. The formation of (BaMg)5Nb4O15 was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg1/3Nb2/3)O3 was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 °C. We produced 5MBN ceramics with these dielectric properties: ?r = 36.69, Qf = 20,097 GHz, and τf = 61.1 ppm/°C, and 10MBN ceramics with these dielectric properties: ?r = 39.2, Qf = 43,878 GHz, and τf = 37.6 ppm/°C. The reaction-sintering process is a simple and effective method for producing (5 − x)BaO-xMgO-2Nb2O5 ceramics for applications in microwave dielectric resonators. 相似文献
4.
The effects of B2O3 addition on the microwave dielectric properties and the microstructures of (1−x)LaAlO3-xSrTiO3 ceramics prepared by conventional solid-state routes have been investigated. Doping with 0.25 wt.% B2O3 can effectively promote the densification and the microwave dielectric properties of (1−x)LaAlO3-xSrTiO3 ceramics. It is found that LaAlO3-SrTiO3 ceramics can be sintered at 1400°C due to the liquid phase effect of a B2O3 addition observed by scanning electronic microscopy (SEM). The dielectric constant as well as the Q×f value decreases with increasing B2O3 content. At 1460°C, 0.46LaAlO3-0.54SrTiO3 ceramics with 0.25 wt.% B2O3 addition possesses a dielectric constant (εr) of 35, a Q×f value of 38,000 (at 7 GHz) and a temperature coefficients of resonant frequency (τf) of −1 ppm/°C. 相似文献
5.
The microwave dielectric properties and the microstructures of the (1−x)MgTiO3-xCaTiO3 ceramic system were investigated. With partial replacement of Mg by Co, dielectric properties of the (1−x)(Mg0.95Co0.05)TiO3-xCaTiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature. At 1275°C, the 0.95(Mg0.95Co0.05)TiO3-0.05CaTiO3 ceramics possesses excellent microwave dielectric properties: a dielectric constant εr of 20.3, a Q×f value of 107 000 ( at 7 GHz) and a τf value of −22.8 ppm/°C. By appropriately adjusting the x value in the (1−x)(Mg0.95Co0.05)TiO3-xCaTiO3 ceramic system, zero τf value can be achieved. With x=0.07, a dielectric constant εγ of 21.6, a Q×f value of 92 000 (at 7 GHz) and a τf value of −1.8 ppm/°C was obtained for 0.93(Mg0.95Co0.05)TiO3-0.07CaTiO3 ceramics sintered at 1275°C for 4 h. 相似文献
6.
The binary lead-free piezoelectric ceramics with the composition of (1 − x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3 were synthesized by conventional mixed-oxide method. The phase structure transformed from rhombohedral to tetragonal phase in the range of 0.16 ≤ x ≤ 0.20. The grain sizes varied with increasing the Bi0.5K0.5TiO3 content. Electrical properties of ceramics are significantly influenced by the Bi0.5K0.5TiO3 content. Two phase transitions at Tt (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and Tc (the Curie temperature) were observed in all the ceramics. Adding Bi0.5K0.5TiO3 content caused the variations of Tt and Tc. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. Besides, the ceramics with homogeneous microstructure and excellent electrical properties were obtained at x = 0.18 and sintered at 1170 °C. The piezoelectric constant d33, the electromechanical coupling factor Kp and the dielectric constant ?r reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037. 相似文献
7.
The microstructures and the microwave dielectric properties of the (1 − x)Mg4Nb2O9-xCaTiO3 ceramic system were investigated. In order to achieve a temperature-stable material, CaTiO3 (τf ∼ 800 ppm/°C) was chosen as a τf compensator and added to Mg4Nb2O9 (τf ∼ −70 ppm/°C) to form a two phase system. It was confirmed by the XRD and EDX analysis. By appropriately adjusting the x-value in the (1 − x)Mg4Nb2O9-xCaTiO3 ceramic system, near-zero τf value can be achieved. A new microwave dielectric material, 0.5Mg4Nb2O9-0.5CaTiO3 applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ?r ∼ 24.8, a Q × f value ∼82,000 GHz (measured at 9.1 GHz) and a τf value ∼−0.3 ppm/°C. 相似文献
8.
S.A. Lokare 《Materials Research Bulletin》2008,43(2):326-332
Electrical and magnetoelectric properties of magnetoelectric (ME) composites containing barium titanate as electrical component and a mixed Ni-Co-Mn ferrite as the magnetic component are reported. The ME composites with a general formula (x)BaTiO3 + (1 − x)Ni0.94Co0.01Mn0.05Fe2O4 where x varies as 0, 0.55, 0.70, 0.85 and 1 were prepared by standard double sintering ceramic method. The presence of both the phases was confirmed by X-ray diffraction technique. The dc resistivity was measured as a function of temperature. The variation of dielectric constant (?) and loss tangent (tan δ) with frequency (100 Hz-1 MHz) and with temperature was studied. The conduction is explained on the basis of small polaron model based on ac conductivity measurements. The static value of ME conversion factor i.e. dc (ME)H was studied as function of intensity of magnetic field. The changes were observed in dielectric properties as well as ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 610 μV/cm Oe was observed in the case of a composite containing 15 mol% ferrite phase. 相似文献
9.
Takeshi Oishi 《Materials Research Bulletin》2007,42(12):2072-2081
The crystal structure and microwave dielectric properties of the (Sm1−xYx)(Ti1.5W0.5)O6 (x = 0 and 0.5) ceramics sintered at 1375 °C for 2-50 h were investigated in this study. No secondary phase was observed in the samples sintered for various sintering times, whereas a secondary phase was formed in the (Sm0.5Y0.5)(Ti1.5W0.5)O6 ceramic sintered at 1400 °C for 50 h. As for the microstructure analysis, the formation of the liquid phase was observed in the both of the samples sintered for 20 and 50 h. The formation of the liquid phase is related to the compositional change of Ti and W from the stoichiometric composition of the samples caused by the instability of crystal structure. The dielectric constants were increased with increased sintering time in the both of the samples, though variations in the temperature coefficient of resonant frequency of the samples were not recognized with the variation in the sintering time. Moreover, although the quality factors of the each sample increased with increasing the sintering time from 2 to 10 h, decreases in the quality factors were recognized when the sintering time was over 10 h. 相似文献
10.
We prepared Ba(Ti1−xSnx)O3 powders and ceramics by means of the sol-gel process, with dibutyltin dilaurate as the Sn precursor. The samples were characterized by means of Fourier-transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy, and also determined the dielectric properties of the ceramics. The powders synthesized by means of the sol-gel process had a grain size on the nanometer scale, with the grains mainly composed of a cubic BaTiO3 phase. Sn can disperse into BaTiO3 more uniformly in the sol-gel technique using dibutyltin dilaurate as the Sn precursor. With increasing Sn concentration, the grain size of the Ba(Ti1-xSnx)O3 ceramics increased and the maximum dielectric constant (?max) first increased and then decreased. At a Sn concentration of 5 mol%, ?max reached its maximum value (19,235). 相似文献
11.
Tai-Kwang Park 《Materials Research Bulletin》2008,43(3):730-734
Ceramic powders of (Ba,Pb)Pb(Mg1/3Ta2/3)O3 were prepared via a B-site precursor route. Crystal symmetries and lattice parameters were determined. Monophasic perovskite was developed after the two-step reaction process, in which the lattice parameters showed linear changes in the entire composition range. Dielectric responses of the ceramics with compositional and frequency changes were investigated. The results were also compared with the (Ba,Pb)(Zn1/3Ta2/3)O3 data. 相似文献
12.
New dielectric material system of x(Mg0.95Zn0.05Ti)O3-(1 − x)Ca0.8Sm0.4/3TiO3 at microwave frequency
The microstructures and the microwave dielectric properties of the x(Mg0.95Zn0.05)TiO3-(1 − x) Ca0.8Sm0.4/3TiO3 ceramic system were investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. Ca0.8Sm0.4/3TiO3 has dielectric properties of dielectric constant εr ~ 120, Q × f value ~ 13,800 GHz and a large positive τf value ~ 400 ppm/°C. (Mg0.95Zn0.05)TiO3 possesses high dielectric constant (εr ~ 16.21), high quality factor (Q × f value ~ 210,000 at 9 GHz) and negative τf value (− 59 ppm/°C). Sintering at 1300 °C with x = 0.9, 0.9(Mg0.95Zn0.05Ti)O3 − 0.1 Ca0.8Sm0.4/3TiO3 has a dielectric constant (εr) of 22.7, a Q × f value of 124,000 GHz and a temperature coefficient of resonant frequency (τf) of − 6.3 ppm/°C. 相似文献
13.
La modified Pb(Mg1/2W1/2)O3 were prepared by solid-state reaction process, and the sintering behavior, microstructure and microwave dielectric properties were investigated by X-ray powder diffraction (XRD), Raman scattering and HP network analyzer in this paper. A series of single phase perovskite type solid solutions with A-site vacancies (Pb1−3x/2Lax(Mg1/2W1/2)O3 (0 ≤ x ≤ 2/3)) were formed. The solid solution took cubic perovskite type structure (Fm3m) with random distribution of A-site vacancies when 0 < x < 0.5, and tetragonal or orthorhombic structure with the ordering of A-site vacancies when 0.5 ≤ x ≤ 2/3. The dielectric constant and temperature coefficient of resonant frequency decrease with increasing La content. Relatively good combination microwave dielectric properties were obtained for x = 0.56: ?r = 28.7; Q × f = 18098; and τf = −5.8 ppm/°C. 相似文献
14.
Abdul Samee Fawzi 《Materials Research Bulletin》2010,45(8):1000-1007
The structural, electrical, dielectric, magnetic and magnetoelectric properties of (x)Ni0.8Zn0.2Fe2O4 + (1 − x)Pb0.93La0.07(Zr0.60Ti0.40)O3 (x = 0, 0.15, 0.30, 0.45 and 1) have been studied by means of various experimental techniques. Polycrystalline samples of this series have been prepared by the double sintering ceramic method. X-ray diffraction data analysis revealed purity of the composites. Microstructural analysis using scanning electron microscopy mode depicts the presence of two phases in contact with each other. Dielectric properties were studied at and well above room temperature. Temperature dependent variation of the dielectric constant show diffused phase transition which can be well described by fitting the Lorentz-type relation, . Observation of well-saturated ferroelectric hysteresis loop and magnetic hysteresis loop for composites indicates that ferroelectric and magnetic ordering exist simultaneously at room temperature. The static value of magneto electric voltage coefficient (αE) has been studied as a function of magnetic field at room temperature for all the composites. The maximum value of αE is 7.53 mV/(cm Oe) for 85% PLZT-15% NZFO composites. 相似文献
15.
The microwave dielectric properties and the microstructures of Nd(Co1/2Ti1/2)O3 ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. It is found that low-level doping of B2O3 (up to 0.75 wt.%) can significantly improve the density and dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics. Nd(Co1/2Ti1/2)O3 ceramics with additives could be sintered to a theoretical density higher than 98.5% at 1320 °C. Second phases were not observed at the level of 0.25-0.75 wt.% B2O3 addition. The temperature coefficient of resonant frequency (τf) was not significantly affected, while the dielectric constants (?r) and the unloaded quality factors Q were effectively promoted by B2O3 addition. At 1320 °C/4 h, Nd(Co1/2Ti1/2)O3 ceramics with 0.75 wt.% B2O3 addition possesses a dielectric constant (?r) of 27.2, a Q × f value of 153,000 GHz (at 9 GHz) and a temperature coefficient of resonant frequency (τf) of 0 ppm/°C. The B2O3-doped Nd(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature. 相似文献
16.
In this study, bulk ceramics with general formula Bi1−ySryFe(1−y)(1−x)Sc(1−y)xTiyO3 (x = 0-0.2, y = 0.1-0.3 mol%) were prepared by traditional solid-state reaction method. As a comparison, bulk BiFeO3 (BF) was also sintered by rapid sintering method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that apart from a small amount of secondary phase detected in BF, all other samples crystallized in pure perovskite structure and maintained original R3c space group. The room temperature M-H curves were obtained. While BF had a coercive magnetic field (Hc) of 150 Oe, Bi1−ySryFe1−yTiyO3 solid solutions had a much larger value (for y = 0.1, 0.2, 0.3, Hc were 4537, 5230 and 3578 Oe, respectively). Sc3+ substitution decreased the Hc values of these solid solutions remarkably, and resulted in soft magnetic properties, as well as a decrease of the dielectric loss. At 1 MHz, the tan δ of Bi0.7Sr0.3Fe0.7(1−x)Sc0.7xTi0.3O3 with x = 0.05, 0.1, 0.15, 0.2 were 0.1545, 0.1078, 0.1046 and 0.1701, respectively. 相似文献
17.
C. Karthik 《Materials Research Bulletin》2008,43(11):3026-3036
The (0 0 l) textured BaBi2(Nb1 − xVx)2O9 (where x = 0, 0.03, 0.07, 0.1 and 0.13) ceramics were fabricated via the conventional melt-quenching technique followed by high temperature heat-treatment (800-1000 °C range). The influence of vanadium content and sintering temperature on the texture development and relative density were investigated. The samples corresponding to the composition x = 0.1 sintered at 1000 °C for 10 h exhibited the maximum orientation of about 67%. The Scanning electron microscopic studies revealed the presence of platy grains having the a-b planes perpendicular the pressing axis. The dielectric constant and the pyroelectric co-efficient values in the direction perpendicular to the pressing axis were higher. The anisotropy in the dielectric constant is about 100 (at 100 kHz) at the dielectric maximum temperature and anisotropy in the pyroelectric co-efficient is about 50 μC cm−2 °C−1 in the vicinity of pyroelectric anomaly for the sample corresponding to the composition x = 0.1 sintered at 1000 °C. Higher values of the dielectric loss and electrical conductivity were observed in the direction perpendicular to the pressing axis which is attributed to the high oxygen ion conduction in the a-b planes. 相似文献
18.
R.V.K. Mangalam 《Materials Research Bulletin》2009,44(3):576-36
The ferromagnetic metallic oxide, SrRuO3 (TC ∼ 165 K) undergoes structural, magnetic and metal-insulator transitions upon substitution of Cu at the Ru-site. For x = 0.2 in SrRu1−xCuxO3, the structure becomes a tetragonal with the space group I4/mcm and there is a signature of both ferromagnetic (TC = 65 K) and antiferromagnetic (TN = 32 K) ordering due to possible magnetic phase separation. The antiferromagnetism arises due to short range ordering of Cu- and Ru-moments. Jahn-Teller distortion of (Ru,Cu)-O6 octahedra indicates that the copper ions are in 2+ oxidation state with 6t2g3eg electronic configuration. For x ≥ 0.1, narrowing of Ru-4d bandwidth by the substitution of Cu ions results in semiconducting behavior. For x = 0.3, the ac and dc susceptibility measurements indicate a spin glass behavior. The origin of spin glass behavior has been attributed to competing ferromagnetic and antiferromagnetic interactions. 相似文献
19.
Stoichiometric lead magnesium niobate, Pb(Mg1/3Nb2/3)O3 (PMN), perovskite ceramics produced by reaction-sintering process were investigated. Without calcination, a mixture of PbO, Nb2O5, and Mg(NO3)2 was pressed and sintered directly. Stoichiometric PMN ceramics of 100% perovskite phase were obtained for 1, 2, and 4 h sintering at 1250 and 1270 °C. PMN ceramics with density 8.09 g/cm3 (99.5% of theoretical density 8.13 g/cm3) and Kmax 19,900 under 1 kHz were obtained. 相似文献
20.
ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2) ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of compound and to improve the sinterability. One wt.% of V2O5 and B2O3 with the mole ratios of 3:1 were used to lower the sintering temperature of ceramics. The effect of Sn content on phase structure and dielectric properties were investigated. The results show that the substituting Sn for Ti accelerates the hexagonal phase transition to cubic phase, and an inverse spinel structure Zn2(Ti1−xSnx)O4 solid solution forms. The best dielectric properties obtained at x = 0.12. The ZnO-0.88TiO2-0.12SnO2 ceramics sintered at 900 °C exhibit a good dielectric property: ?r = 29 and tan δ = 9.86 × 10−5. Due to their good dielectric properties, low firing characteristics, ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2) can serve as the promising microwave dielectric capacitor. 相似文献