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Ulrich Weber Georg Greuel Ulrich Boettger Sophie Weber Detlev Hennings Rainer Waser 《Journal of the American Ceramic Society》2001,84(4):759-766
The purpose of the present investigation is to describe the influence of the processing parameters on the dielectric behavior of manganese-doped Ba(Ti1− x Zr x )O3 ceramics, particularly variations in the small-signal aging rate, temperature characteristic, and hysteresis. In this paper, the aging behavior of base-metal electrode materials above the temperature of the permittivity maximum ( T M ), including the influence of the zirconium content and annealing conditions, is described for the first time. The aging rate at temperatures greater than T M decreases as the oxygen partial pressure increases during annealing and the zirconium content increases, whereas the aging rate exhibits a maximum at temperatures much less than T M . The behavior is explained in terms of a diffuse phase transition. Hysteresis-loop deformation is observed during aging. 相似文献
3.
X7R-type BaTiO3 materials were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Powder XRD indicated that the materials had pseudocubic lattices, but core–shell grain structures predominated in bright-field (BF) TEM images. Electron diffraction patterns across the core–shell boundaries and convergent beam electron diffraction patterns of cores and shells indicated that coherent grain boundaries existed between cores and shells. The flat dielectric constant–temperature curves obtained from these materials can be interpreted in terms of the internal stress states in individual grains. The stress states were observed using weak-beam dark-field (WBDF) microscopy, and strain contours formed by distorted crystal planes were visible in the WBDF images. The contours observed were dependent on the stress state of the crystal instead of crystal symmetry and the stress distribution in individual grains was determined by both the thickness ratio of shell and core, and the geometrical relationship of the core and the shell. Twins observed in this material were determined to be growth rather than mechanical twins, through observation of the strain contour distribution. 相似文献
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Sven van der Gijp Johan E. ten Elshof Oliver Steigelmann Henk Verweij 《Journal of the American Ceramic Society》2000,83(10):2610-2612
The influence of mechanical stress and chemical homogeneity on the permittivity of BaTi0.9 Zr0.1 O3 ceramics prepared from mixed-oxide and hydrothermal powders was studied. To reduce stress, liquid-phase sintering was applied in conjunction with a low heating rate to stimulate the formation of large grains. The influence of chemical homogeneity was studied by variations in sintering temperatures and times. For both types of ceramics, the dielectric constant at the Curie temperature was influenced by both factors, but to a different extent. In the mixed oxide ceramic, chemical homogeneity played a more prominent role, while internal stress appeared to exert a larger influence in the hydrothermal ceramics. The dielectric constant at the Curie temperature could be increased by 5%–10% by an annealing treatment at 200°C, followed by slow cooling. 相似文献
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The high-temperature equilibrium electrical conductivity of Ce-doped BaTiO3 was studied in terms of oxygen partial pressure, P (O2 ), and composition. In (Ba1−x Ce x )TiO3 , the conductivity follows the −1/4 power dependence of P (O2 ) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P (O2 ) where electron compensation prevails at low P (O2 ). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO3 , indicating the substitution of Ce as Ce4+ for Ti4+ in Ba(Ti1−y Ce y )O3 . The Curie temperature ( T c ) was systematically lowered when Ce3+ was incorporated into Ba2+ sites, whereas the substitution of Ce4+ for Ti4+ sites resulted in no change in this parameter. 相似文献
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Dong-Wan Kim Jeong-Ryeol Kim Sung-Hun Yoon Kug Sun Hong Chang Kyung Kim 《Journal of the American Ceramic Society》2002,85(11):2759-2762
The effect of B2 O3 on the sintering temperature and microwave dielectric properties of Ba5 Nb4 O15 has been investigated using X-ray powder diffraction, scanning electron microscopy, and a network analyzer. Interactions between Ba5 Nb4 O15 and B2 O3 led to formation of second phases, BaNb2 O6 and BaB2 O4 . The addition of B2 O3 to Ba5 Nb4 O15 resulted in lowering the sintering temperature from 1400° to 925°C. Low-fired Ba5 Nb4 O15 could be interpreted by measuring changes in the quality factor ( Q × f ), the relative dielectric constant (ɛr ), and the temperature coefficient of resonant frequency (τf ) as a function of B2 O3 additions. More importantly, the formation of BaNb2 O6 provided temperature compensation. The microwave dielectric properties of low-fired Ba5 Nb4 O15 had good dielectric properties: Q × f = 18700 GHz, ɛr = 39, and τf = 0 ppm/°C. 相似文献
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Detlev F. K. Hennings B. Seriyati Schreinemacher Herbert Schreinemacher 《Journal of the American Ceramic Society》2001,84(12):2777-2782
BaTiO3 and Ba(Ti,Zr)O3 dielectric powders have been prepared from submicrometer BaCO3 , TiO2 , and ZrO2 . By use of submicrometer BaCO3 the intermediate formation of Ba2 TiO4 second phase can be widely suppressed. Monophase perovskites of BaTiO3 were already formed at 900°C and Ba(Ti,Zr)O3 at 1050°C. Aggregates of very small subgrains could be easily disintegrated to particle sizes <0.5 μm. 相似文献
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Héctor Beltrán Eloisa Cordoncillo Purificación Escribano Derek C. Sinclair Anthony R. West 《Journal of the American Ceramic Society》2004,87(11):2132-2134
Samples of composition Ba1− x La x Ti1− x /4 O3 , x = 0, 0.003, 0.03, and 0.10, were prepared by an alkoxide sol–gel route with final firing of ceramics at 1100°C, 2 h in air. All samples showed bulk insulating behavior with no evidence of semiconductivity caused by either direct donor doping or oxygen loss. 相似文献
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Toshimasa Suzuki Mitsuo Ueno Yuji Nishi Masayuki Fujimoto 《Journal of the American Ceramic Society》2001,84(1):200-206
Dislocation loops observed in nonstoichiometric and stoichiometric (Ba,Ca)TiO3 , and in stoichiometric BaTiO3 sintered in a reducing atmosphere, were characterized by conventional transmission electron microscopy (TEM) under two-beam conditions and high-resolution TEM atomic structure analysis. Dislocation loops mostly lay on {100} planes with Burgers vectors of type 〈100〉. The dynamic behavior of these dislocation loops during the electron beam irradiation (EBI), however, was classified into two different types of dislocation loops: in A-site-excess (Ba,Ca)TiO3 , contrasts of dislocation loops faded completely away; in BaTiO3 and B-site-excess (Ba,Ca)TiO3 , fine-line contrasts remained. Dislocation loops with Burgers vectors of type 1/2〈100〉 and the resultant crystallographic shear (CS) structure with a displacement vector of type 1/2〈110〉 after EBI were proposed to interpret residual line images. Disappearance of these line images in A-site-excess (Ba,Ca)TiO3 strongly suggests preferential Ca ion site occupancy at the CS structure. 相似文献
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Jung-In Yang Sahn Nahm Chang-Hack Choi Hwack-Joo Lee Hyun-Min Park 《Journal of the American Ceramic Society》2002,85(1):165-168
The effect of ZrO2 on crystallographic order, microstructure, and microwave dielectric properties of Ba(Zn1/3 Ta2/3 )O3 (BZT) ceramics was investigated. A small amount of ZrO2 disturbed the 1:2 cation ordering. The average grain size of the BZT significantly increased with the addition of ZrO2 , which was attributed to liquid-phase formation. The relative density increased with the addition of a small amount of ZrO2 , but it decreased when the ZrO2 content was increased. Variation of the dielectric constant with ZrO2 addition ranged between 27 and 30, and the temperature coefficient of resonant frequency increased abruptly as the ZrO2 amount exceeded 2.0 mol%. The Q value of the BZT significantly improved with the addition of ZrO2 , which could be explained by the increased relative density and grain size. The maximum Q × f value achieved in this investigation was ∼164 000 GHz for the BZT with 2.0 mol% ZrO2 sintered at 1550°C for 10 h. 相似文献
11.
Paula M. Vilarinho Liqin Zhou Manfred Pöckl Nelson Marques João L. Baptista 《Journal of the American Ceramic Society》2000,83(5):1149-1152
The dielectric properties of (1− x )Pb(Fe2/3 W1/3 )O3 · x PbTiO3 solid solutions were investigated from 102 to 106 Hz in the temperature range 150–600 K. The phase transition of Pb(Fe2/3 W1/3 )O3 (PFW) was shifted by PbTiO3 (PT) additions to higher temperatures at a rate of 6.3 K/mol% of PT. The temperature dependence of dielectric permittivity showed a sharper transition as the PT content increased. Dielectric measurements in a wide temperature range showed the presence of a second set of dielectric peaks at higher temperatures (350–600 K), besides the ferroelectric–paraelectric phase transition. This second set of peaks vanished when the samples were annealed in nitrogen. The activation energy values for the second relaxation varied between 0.50 and 0.63 eV, in agreement with the conduction activation energy determined for each sample. This relaxation is apparently related to electron holes. 相似文献
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Scanning tunneling microscopy (STM) and spectroscopy (STS) have been applied to study the surface electronic properties of n -type BaTiO3 ceramics under ultrahigh vacuum and at various oxygen partial pressures. I – V tunneling characteristics of vacuum-annealed BaTiO3 do not exhibit rectifying behavior, implying that the Fermi level is pinned at the surface. The surface band gap of BaTiO3 annealed under vacuum at 540°C is equal to 1 eV. The top edge of the surface valence band is located 0.7 eV below the Fermi level. Hysteresis in the I – V characteristics has been observed at high oxygen partial pressures. Dosing of the BaTiO3 with oxygen increases the surface band gap and unpins the Fermi level. As a result, the I – V characteristics acquire rectifying features similar to those observed for BaTiO3 Schottky-type diodes. Hysteresis in the I – V spectra observed at high oxygen partial pressures is attributed to the changes of the surface potential barrier due to adsorption/desorption of oxygen modulated by the tip-sample potential difference. 相似文献
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The BiVO4 additive was found effective for low-temperature firing of ZnNb2 O6 polycrystalline ceramics below 950°C in air without a serious degradation in their microwave dielectric properties. Dense BiVO4 -doped ZnNb2 O6 samples of a relative sintered density over 95% could be prepared even at 925°C. An optimally processed specimen exhibited excellent microwave dielectric properties of Q · f = 55000 GHz, ɛr = 26, and τf =−57 ppm/°C. With increasing BiVO4 addition up to 20 mol% relative to ZnNb2 O6 , while the quality factor Q · f was gradually decreased, the relative dielectric constant, ɛr , was linearly increased and the temperature coefficient of resonant frequency, τf , was slightly increased. The variations in Q · f and ɛr are surely attributable to the residual BiVO4 in the ZnNb2 O6 matrix. An unexpected slight increase in τf is probably due to the formation of the Bi(V,Nb)O4 -type solid solution. 相似文献
14.
Sergey Kucheiko Dong-Hun Yeo Ji-Won Choi Seok-Jin Yoon Hyun-Jai Kim 《Journal of the American Ceramic Society》2002,85(5):1327-1329
The microwave dielectric properties of CaTi1− x (Al1/2 Nb1/2 ) x O3 solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO3 . The substitution of Ti4+ by Al3+ /Nb5+ improved the quality factor Q of the sintered specimens. A small addition of Li3 NbO4 (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛr ) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τf ) of −2 ppm/K. Li3 NbO4 as a sintering additive had no harmful influence on τf of ceramics. 相似文献
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Dielectric ceramics in the system (Zn1− x Co x )TiO3 ( x = 0–1) were synthesized by the solid-state reaction route. The phase distribution, microstructure, and dielectric properties were characterized by using powder X-ray diffraction analysis, electron microscopy, and microwave measurement techniques. Three phase composition regions were identified in the specimens sintered at 1150°C; [spinel + rutile] at 0 ≤ x ≤ 0.5, [spinel + ilmenite + rutile] at 0.5 < x ≤ 0.7, and [ilmenite] phase at 0.7 < x ≤ 1. For the 0 ≤ x ≤ 0.5 region, the amount of Ti-rich precipitates incorporated into the spinel phase decreased with the Co content at 0 ≤ x ≤ 0.5, with a concomitant increase of the rutile phase. The ilmenite phase appeared for high Co content. The microwave dielectric properties depended on the phase composition and volume according to the three phase regions, where the relative amount of rutile to the spinel or ilmenite determined the dielectric properties. The dielectric constant as a function of Co addition was modeled with a Maxwell mixing rule. An optimum phase distribution was determined in this system with dielectric constant of 25, a Q * f 70 000 GHz, and a low temperature coefficient of the resonant frequency. 相似文献
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The crystallization and dielectric properties of SrO–BaO–Nb2 O5 –SiO2 glass-ceramics have been investigated. Glass-ceramics that contain strontium barium niobate (SBN) as a primary crystalline phase, which has a tungsten bronze structure, are produced. The formation of crystalline secondary phases also has been studied. The SBN phase shows evidence of both surface nucleation and bulk nucleation, and the crystals have an average composition of Sr0.47 Ba0.53 Nb2 O6 . The dendritic morphology of the SBN crystals has been examined. The SBN content and composite dielectric constant each has been studied as a function of heating temperature/time. The highest SBN content and dielectric constant obtained in the present study are 42 vol% and 180, respectively. The dielectric constant of the glass-ceramics is determined primarily by the SBN content and the residual glass phase. The dielectric constant of the randomly oriented SBN crystal in the glass-ceramics is calculated, using dielectric mixture rules, to be ∼400. 相似文献
17.
Joon Yeob Cho Ki Hyun Yoon Eung Soo Kim 《Journal of the American Ceramic Society》2003,86(8):1330-1332
Effect of geometrical shape and induced thermal strain on the microwave dielectric properties of the layered structure ceramics of Mg0.93 Ca0.07 TiO3 with (Ca0.3 Li0.14 Sm0.42 )TiO3 was investigated as a function of the number of dielectric layers. The dielectric constant and the temperature coefficient of resonant frequency (TCF) were not changed significantly with the number of dielectric layers but only depended on the net compositional ratio. However, the dielectric loss quality was affected by the number of interfaces between dielectric layers, which had a partial composition inhomogeneity due to the diffusion of Mg2+ and Ti4+ ions. The dielectric loss quality also decreased with an increase of thermal strain induced to each dielectric layer. 相似文献
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Maria Teresa Buscaglia Massimo Viviani Vincenzo Buscaglia Carlo Bottino Paolo Nanni 《Journal of the American Ceramic Society》2002,85(6):1569-1575
The incorporation of Er3+ into BaTiO3 ceramics was investigated on samples containing 0.25, 0.5, 1, 2, 8, and 10 at.% of dopant, after sintering at 1350–1550°C in air. For Er3+ concentrations ≤1 at.%, dense and large-grained ceramics with low room-temperature resistivity (102 –103 Ω·cm) were obtained. The observed properties are largely independent of stoichiometry. Simultaneous substitution of Er3+ at both cation sites, with higher preference for the Ba site, is proposed. The behavior of heavily doped ceramics depends on stoichiometry. When Ba/Ti < 1, the electrical properties change from slightly semiconducting to insulating as Er concentration increases from 2 to 8 at.%. The ceramics have tetragonal perovskite structure and contain a large amount of Er2 Ti2 O7 pyrochlore phase. On the other hand, when Ba/Ti > 1, the ceramics are insulating, fine-grained, and single phase. In this case, incorporation of Er3+ predominantly occurs at the Ti site, with oxygen vacancy compensation. Incorporation is accompanied by a significant reduction of tetragonality and by expansion of the unit cell. The different results indicate that Er3+ solubility at the Ba site does not exceed 1 at.%, whereas solubility at the Ti site is at least 10 at.%. However, the incorporation of Er3+ and the resulting properties are also strongly affected by sintering conditions. 相似文献
19.
Pavol Juhás Peter K. Davies Mehmet A. Akbas 《Journal of the American Ceramic Society》2004,87(11):2086-2092
The structure and dielectric properties of (1− x )Pb(Sc2/3 W1/3 )O3 –( x )Pb(Zr/Ti)O3 ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x ≤ 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc2/3 W1/3 )O3 (PSW) can be described by a random-site model with one cation site occupied by Sc3+ and the other by a random distribution of (Sc1/3 3+ W2/3 6+ ). The ordering is destabilized in solid solutions of PSW with PbZrO3 (PSW–PZ), but stabilized by PbTiO3 in the (1− x )PSW–( x )PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW–PZ the temperature of the permittivity maximum ( T ɛ,max ) increases linearly with x ; however, for PSW–PT T ɛ,max decreases in the ordered region (up to x = 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW–(0.25)PT; when the order parameter was reduced from ∼1.0 to ∼0.65, T ɛ,max increased by more than 60°C. 相似文献
20.
Dong-Wan Kim Do-Kyun Kwon Kug Sun Hong Deug Joong Kim 《Journal of the American Ceramic Society》2003,86(5):795-799
Samples of 1/6Ba5 Nb4 O15 ·5/6BaNb2 O6 along with the pure end members, Ba5 Nb4 O15 and BaNb2 O6 , were sintered under low oxygen partial pressure. The degradation mechanisms of dielectric loss in this reducing atmosphere have been studied. We found that the degradation occurred primarily due to the formation of oxygen vacancies caused by the reduction of Nb5+ . This was determined by measuring the electrical conductivity, and through X-ray photoelectron spectroscopy. More importantly, the dielectric loss of 1/6Ba5 Nb4 O15 ·5/6BaNb2 O6 samples with higher temperature stability was further decreased on sintering in a reducing atmosphere. This observation has been explained by considering the increased porosity and formation of a reduced second phase, Ba0.65 NbO3 . 相似文献