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1.
Perovskite developments in the Pb(Zn1/3 Ta2/3 )O3 –PbTiO3 system were explored. Formation yields and lattice parameters of the perovskite were determined from X-ray diffractometry results. Weak-field low-frequency dielectric properties of the system ceramics were investigated, followed by microstructure examination. Perovskite started to develop in Pb(Zn1/3 Ta2/3 )O3 after the introduction of 30 mol% PbTiO3 , whereas complete stabilization was accomplished at 60% substitution. Dielectric relaxation behavior was not substantial across the entire composition range, whereas phase transition modes changed from diffuse to sharp with increased PbTiO3 fraction. 相似文献
2.
Keisuke Kageyama 《Journal of the American Ceramic Society》1992,75(7):1767-1771
The microwave dielectric properties and crystal structure of Ba(Zn1/3 Ta2/3 )O3 – (Sr,Ba)(Ga1/2 Ta1/2 )O3 ceramics were investigated in the present study. The Q value of Ba(Zn1/3 Ta2/3 )O3 was improved by adding 5 mol% Sr(Ga1/2 Ta1/2 )O3 . The maximum Q value of Q × f = 162000 GHz was obtained at 0.95Ba(Zn1/3 Ta2/3 )O3 . 0.05Sr(Ga1/2 Ta1/2 )O3 . For this composition, a lattice super structure caused by hexagonal ordering was observed. A further improvement in the Q value was attained when some Sr was replaced with Ba, and 0.95Ba(Zn1/3 Ta2/3 )O3 · 0.05(Sr0.25 Ba0.75 )(Ga1/2 Ta1/2 )O3 exhibited a maximum Q value such that Q × f = 210000 GHz. Despite the increased Q value with the replacement of Sr by Ba, the c/a value, which indicates the degree of lattice distortion, remained constant near 3/2. The Q value thus improved without lattice distortion in the system Ba(Zn1/3 Ta2/3 )O3 -(Sr,Ba)(Ga1/2 Ta1/2 )O3 , whereas the improvement of Q value increased with lattice distortion in the solid solution system with Ba(Zn1/3 Ta2/3 )O3 as an end member. 相似文献
3.
X. M. Chen D. Liu R. Z. Hou X. Hu X. Q. Liu 《Journal of the American Ceramic Society》2004,87(12):2208-2212
Ca(Zn1/3 Nb2/3 )O3 microwave dielectric ceramics were prepared using a solid-state reaction process, and their microwave dielectric properties were evaluated as functions of sintering and postdensification annealing conditions. The relationship between microwave dielectric properties and processing was interpreted through the variation of microstructures. The dielectric constant showed slight variation with sintering and annealing conditions, but the Q × f value increased at first and then decreased with increased sintering temperature, and annealing in oxygen indicated significant improvement in Q × f , especially for the specimens sintered at higher temperatures. The good microwave dielectric properties were obtained in the ceramics sintered at 1225°C in air for 3 h and annealed at 1100°C in oxygen for 8 h: ɛ= 34.1, Q × f = 15 890 GHz, τf =−48 ppm/°C. 相似文献
4.
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
5.
The compositional dependence of microwave dielectric properties has been investigated in the (1 − x )(Na1/2 Nd1/2 )TiO3 − x Nd(Mg1/2 Ti1/2 )O3 (NNT-NMT) system. The addition of NMT results in significant improvement in the quality factor and the temperature coefficient of frequency, but gradually decreases the dielectric constant from ∼100 for pure NNT to ∼25 for pure NMT. The single perovskite phase is observed with various { hkl } superlattice reflections over the entire compositional range. The increasing tendency of peak splitting with increasing x at some perovskite reflections strongly suggests that the crystal structure of the system changes to lower symmetry structures. This is confirmed using infrared reflectivity spectra. The superlattice reflections related to structural deviation become more predominant as the composition reaches pure NMT. Particularly, {111} superlattice reflections are believed to be associated with the 1:1 cation ordering and responsible for the observed abrupt increase in quality factor at x > 0.7. 相似文献
6.
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
7.
Lai-Cheng Tien Chen-Chia Chou Dah-Shyang Tsai 《Journal of the American Ceramic Society》2000,83(8):2074-2078
Both 1:2 and 1:1 ordered structures form in the perovskite solid solutions of La-substituted BMT Ba1− x La x (Mg(1+ x )/3 Ta(2− x )/3 )O3 , sintered at 1600°C. The 1:2 ordered structure exists in the composition range 0.0 ≤ x ≤ 0.12, while that of 1:1 ordered structure exists in a wider composition range 0.04 ≤ x ≤ 1.0. Two ordered phases coexist in 0.04 ≤ x ≤ 0.12. High-resolution micrographs indicate that 1:2 and 1:1 ordered domains coexist in one grain. The ordering parameter of 1:2 phase decreases with x , yet that of 1:1 phase increases with x . Both increase with soak time. Variations in ordering are discussed in terms of cation occupancy and crystal chemistry. The quality factor increases with x , reaches a maximum, then decreases with x . The dielectric constant increases with x first, and levels off. 相似文献
8.
The structure and temperature dependence of complex lead perovskite dielectrics were investigated for the system (1 − x )Pb(Yb1/2 Ta1/2 )O3 – x Pb(Lu1/2 Nb1/2 )O3 . Superlattice reflections for the compositions 0.8 < x < 1.0 were observed by X-ray diffractometry, and the temperature-composition dielectric-state diagram was determined. In the present study, the disordered middle composition, with 0.2 < x < 0.8, showed a diffuse paraelectric–ferroelectric phase transition, whereas the ordered end compositions, with 0 ≤ x < 0.2 and 0.8 < x ≤ 1.0, revealed successive sharp paraelectric–antiferroelectric and weak antiferroelectric–ferroelectric phase transitions. The dielectric state was confirmed by examining the variation of polarization ( P ) with electric field ( E ). 相似文献
9.
10.
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
11.
Stephen J. Webb Jonathan Breeze Robert I. Scott David S. Cannell David M. Iddles Neil McN. Alford 《Journal of the American Ceramic Society》2002,85(7):1753-1756
Resonators of Ba(Zn1/3 Ta2/3 )O3 , sintered between 1450° and 1600°C, are characterized by Raman spectroscopy, X-ray diffraction, and scanning electron microscopy. The quality factors of the resonators are found to depend on sintering temperature, and at 1600°C there is evidence of Zn loss from the surface. The frequency of the A1g Raman mode changes from 800.9 cm−1 for a sample with Q = 80000 (2 GHz), to 794.5 cm−1 when Q = 44000 (2 GHz). Changes in the position of this and other Raman modes are thought to be due to distortions of the oxygen octahedra, brought about by Zn loss. The presence of a BaTa2 O6 phase at the surface is confirmed by XRD and SEM. 相似文献
12.
SYUNICHIRO KAWASHIMA MASAMITSU NISHIDA ICHIRO UEDA HIROMU OUCHI 《Journal of the American Ceramic Society》1983,66(6):421-423
The dielectric properties at microwave frequencies of Ba(Zn1/3 Ta2/3 )O3 ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot-pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X-ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics. 相似文献
13.
Hyo Tae Kim Thomas Shrout Clive Randall Michael Lanagan 《Journal of the American Ceramic Society》2002,85(11):2738-2744
The sintering behavior and dielectric properties of perovskite Ag(Nb1− x Ta x )O3 (0 < x < 1) solid solutions and two-phase composite assemblages were explored. A small amount of CuO (1 wt%) was used for liquid-phase sintering and led to high densification at temperatures <950°C. The temperature coefficient of capacitance, TCC, was adjusted by varying the Nb:Ta ratio within the solid-solution series and by creating composite microstructures. Two-phase assemblages consisting of Ag(Nb3/4 Ta1/4 )O3 and Ag(Nb1/4 Ta3/4 )O3 were synthesized to achieve a temperature-stable dielectric material for high-frequency applications. The composite dielectric with CuO addition had an average dielectric constant of 390 and a Q × f factor of 410 GHz at 2 GHz, with a stable TCC (0 to −180 ppm/°C) in the temperature range from −20° to +60°C. In addition, process compatibility with a silver conductor was confirmed by high-frequency ring-resonator measurements and microstructural characterization. The Ag(Nb1− x Ta x )O3 solid solutions and composites are promising candidates as embedded capacitors for radio-frequency/microwave applications. 相似文献
14.
15.
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
16.
Jung-Kun Lee Kug-Sun Hong Jin-Wook Jang 《Journal of the American Ceramic Society》2001,84(9):2001-2006
The effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ɛ( T ) curves, D – E hysteresis, and transmission electron microscopy. Although Ti-excess samples showed abnormal grain growth and a decrease of room-temperature permittivity due to a liquid phase at grain boundaries, its ferroelectric properties were similar to those of stoichiometric BaTiO3 ceramics. However, in Ba-excess samples, an increase of permittivity and ferroelectric properties different from those of stoichiometry were found. Changes in domain width and ferroelectric transition behavior indicated that the variation of dielectric properties was related to the internal stress. It is proposed that this internal stress originated from differences in the thermal expansion coefficient between the matrix and the second phase. 相似文献
17.
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
18.
Xingsen Gao Junmin Xue John Wang Ting Yu Ze Xiang Shen 《Journal of the American Ceramic Society》2003,86(5):791-794
0.6Pb(Ni1/2 W1/2 )O3 ·0.4PbTiO3 (0.6PNW·0.4PT) of complex perovskite structure is successfully synthesized by mechanical activation of mixed oxide composition, followed by sintering at 950°C. It exhibits a considerably stable temperature dependence of dielectric constant over the wide temperature range of −120° to 20°C, although there occurs a dielectric peak at around 74°C. Raman spectroscopic studies show the coexistence of tetragonal and pseudocubic perovskite phases on sintering at 950°C, which are attributed to the inhomogeneous distribution of PbTiO3 arising from mechanical activation. The dielectric behavior can be fine tuned by thermal annealing at 750°C, leading to phase redistribution in PNW-PT. 相似文献
19.
Do-Kyun Kwon Clive A. Randall Thomas R. Shrout Michael T. Lanagan 《Journal of the American Ceramic Society》2004,87(6):1088-1092
The dielectric properties and frequency dispersion associated with a dielectric relaxation were evaluated within the perovskite (1− x )BiScO3 – x Ba(Mg1/3 Nb2/3 )O3 solid solution systems (0.7 ≤ x ≤ 1). With increasing BiScO3 , the room-temperature dielectric permittivity at low frequency (100 Hz) increased up to 115 at x = 0.7, and a dielectric relaxation phenomenon was evident. Relaxation parameters were analyzed using several Arrhenius-type equations, and the microwave dielectric property measurement using rectangular wave-guide method enabled confirmation of the extrapolated value of the Arrhenius plot. The result of the microwave dielectric property measurement was also checked with J -function fitting based on the frequency-dependent Gaussian distribution of the associated dielectric loss data at low frequency. 相似文献
20.
Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》2001,84(10):2445-2447
Intermetallic CoAl powder has been prepared via self-propagating high-temperature synthesis (SHS). Dense CoAl materials (99.6% of theoretical) with the combined additions of ZrO2 (3Y) and Al2 O3 have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The microstructures are such that tetragonal ZrO2 (0.3 μm) and Al2 O3 (0.5 μm) particles are located at the grain boundaries of the CoAl (8.5 μm) matrix. Improved mechanical properties are obtained; especially the fracture toughness and the bending strength of the materials with ZrO2 (3Y)/Al2 O3 = 16/4 mol% are 3.87 MPa·m1/2 and 1080 MPa, respectively, and high strength (>600 MPa) can be retained up to 1000°C. 相似文献