共查询到20条相似文献,搜索用时 15 毫秒
1.
Senlin Leng Guorong Li Liaoying Zheng Tianbao Wang Qingrui Yin 《Journal of the American Ceramic Society》2009,92(11):2772-2775
As a lead-free positive temperature coefficient of resistivity (PTCR) material, (1– x mol%) BaTiO3 – x mol% (Bi1/2 K1/2 ) TiO3 – y mol% Y2 O3 –0.5 mol% TiO2 (BT– x BKT–2 y Y–0.5TiO2 ) systems were prepared by the conventional solid-state reaction method. All samples containing <2 mol% BKT sintered in air possessed relatively low room-temperature resistivity (ρ25 ) and high positive temperature coefficient (PTC) effect. However, when the BKT content exceeded 2 mol%, the sample was not semiconductive after sintering in air. The effects of sintering schedule on the properties of PTCR ceramics were discussed. The results showed that the optimum composition of BT–1BKT–0.2Y–0.5TiO2 , sintered at 1330°C for not-soaking and then fast quenched in air, achieved rather low ρ25 of 28 Ω·cm and a high jump of resistivity (maximum resistivity [ρmax ]/minimum resistivity [ρmin ]) of 4.0 orders of magnitude with T c about 155°C. The ρ25 of the as-sintered sample could be further reduced to about 10 Ω·cm by annealing in N2 at 450°C for 30 min, accompanied decrease on the PTC effect. 相似文献
2.
Steven M. Pilgrim Mona Massuda Jackie D. Prodey rew P. Ritter 《Journal of the American Ceramic Society》1992,75(7):1964-1969
Compositional variation within the Pb(Mg1/3 Nb2/3 ) O3 –PbTiO3 –(Ba, Sr)TiO3 (hereafter PMN–PT–BT,ST) ternary (6.4% PT% 14.1%, 1.25% BT,ST% 2.5%) results in major changes in induced strain and hysteresis. For the 1.25% BT family, the increase in strain correlates with an increase in T max , while the dielectric loss is uncorrelated with hysteresis and strain. In addition, weak field aging (which is not reset by application of field) shows little effect on strain and hysteresis for drive fields of > 0.2 MV/m. The vary narrow polarization-fields loops (virgin curvesnearly indistinguishable from subsequent cycles) show that weak-field permittivity is a good approximation to the high-field permittivity. is a good approximation to the high-field Permittivity. Although these data clarify the frequency ( T max is linearly dependent on the logarithm of the frequency) effect on weak-field dielectric behavior, they do not directly address the question of meaningful extrapolation of high-field strain with frequency. In particular, the question remains as to whether the high-field permittivity and strain are frequency dependent. In future papers we will address this question by a combination of measurement techniques as functions of frequency. 相似文献
3.
pela Kunej Sreo D. kapin Danilo Suvorov 《Journal of the American Ceramic Society》2009,92(10):2373-2377
In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi2 O3 −TiO2 −Nd2 O3 system at 1100°C. The samples were analyzed using X-ray powder diffraction and scanning electron microscopy with energy- and wavelength-dispersive spectroscopy. A single-phase pyrochlore ceramic was obtained with the addition of 4.5 mol% of Nd2 O3 . We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi(1.6–1.08 x ) Nd x Ti2 O(6.4+0.3 x ) , where 0.25< x <0.96; (ii) the solid solution Bi4− x Nd x Ti3 O12 , where 0< x <2.6; and (iii) the Nd2− x Bi x Ti2 O7 solid solution, where 0< x <0.35. The determined phase relations in the pyrochlore-rich part are presented in a partial phase diagram of the Bi2 O3 −TiO2 −Nd2 O3 system in air at 1100°C. 相似文献
4.
HIROSHI HIRASHIMA KOTA NISHII TETSURO YOSHIDA 《Journal of the American Ceramic Society》1983,66(10):704-708
The dc conductivities (σ) of V2 O5 -P2 O5 glasses containing up to 30 mol% TiO2 were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 106 Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V2 O5 -P2 O5 glass. The temperature dependence of σ was exponential with σ = σ0 exp(-W/kT ) in the high-temperature range. When part of the P2 O5 was replaced by TiO2, σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO2 content. 相似文献
5.
Jong Bong Lim Shujun Zhang Namchul Kim Thomas R. Shrout 《Journal of the American Ceramic Society》2009,92(3):679-682
Perovskite solid solution in the (1− x )[0.4BiScO3 –0.6BaTiO3 ]+ x (K1/2 Bi1/2 )TiO3 [BSBT–KBT x ] system was synthesized using conventional sintering and hot-isostatic pressing. Dielectric properties of BSBT ceramics with different dopant levels of KBT were characterized as a function of temperature and frequency for potential use of high-temperature capacitors. The BSBT ceramics with KBT exhibited high dielectric permittivities (ɛr ) (>1700 at RT) and low dielectric loss over the temperature range from 100° to 300°C, with flat temperature coefficients of permittivity (TCɛs). In addition, BSBT ceramics with increasing KBT were observed to possess dielectric relaxation characteristics at temperatures (>RT) as observed in lead-based relaxors. Furthermore, high energy densities, being on the order of 4.0 J/cm3 at 220 kV/cm was observed for the BSBT–KBT20 ceramics from the electric-field polarization behavior. 相似文献
6.
Scanning electron microscopy and electron probe micro-analysis were used to investigate the microstructure of both slow-cooled and quenched polycrystalline BaTiO3 specimens with a small excess of TiO2 (Ba/Ti=0.995 to 0.999) or of BaO (Ba/Ti=1.002 and 1.005). The electron micrographs of polished and etched TiO2 -excess BaTiOs samples, and of fracture surfaces of quenched samples, showed a second phase in the grain boundaries and triple-point regions, whereas no second phase was observed in samples having Ba/Ti=1.000. Microprobe analysis of the second phase gave compositions near that of the reported adjacent phase of higher TiO2 content, Ba6 Ti17 O40 . The results indicate that the solubility of TiO2 in BaTiO3 is <0.1 mol%. 相似文献
7.
In the system TiO2 —Al2 O3 , TiO2 (anatase, tetragonal) solid solutions crystallize at low temperatures (with up to ∼ 22 mol% Al2 O3 ) from amorphous materials prepared by the simultaneous hydrolysis of titanium and aluminum alkoxides. The lattice parameter a is relatively constant regardless of composition, whereas parameter c decreases linearly with increasing Al2 O3 . At higher temperatures, anatase solid solutions transform into TiO2 (rutile) with the formation of α-Al2 O3 . Powder characterization is studied. Pure anatase crystallizes at 220° to 360°C, and the anatase-to-rutile phase transformation occurs at 770° to 850°C. 相似文献
8.
The solubility of TiO2 in tetragonal ZrO2 is 13.8±0.3 mol% ui 1300°C, 14.9±0.2 mol% at 1400°C, and 16.1±0.2 mol% at 1500°C. These solid solutions transform to metastable monoclinic solid solutions without compositional change on cooling to room temperature. 相似文献
9.
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
10.
Ruzhong Zuo Xusheng Fang Chun Ye Longtu Li 《Journal of the American Ceramic Society》2007,90(8):2424-2428
(1− x )(Na0.5 K0.5 )NbO3 –(Bi0.5 K0.5 )TiO3 solid solution ceramics were successfully fabricated, exhibiting a continuous phase transition with changing x at room temperature from orthorhombic, to tetragonal, to cubic, and finally to tetragonal symmetries. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was found at 2–3 mol% (Bi0.5 K0.5 )TiO3 (BKT), which brings about enhanced piezoelectric and electromechanical properties of piezoelectric constant d 33 =192 pC/N and planar electromechanical coupling coefficient k p =45%. The MPB composition has a Curie temperature of 370°–380°C, comparable with that of the widely used PZT materials. These results demonstrate that this system is a promising lead-free piezoelectric candidate material. 相似文献
11.
Sun-Jae Kim Soon-Dong Park Yong Hwan Jeong Sung Park 《Journal of the American Ceramic Society》1999,82(4):927-932
Crystalline TiO2 powders were prepared by the homogeneous precipitation method simply by heating and stirring an aqueous TiOCl2 solution with a Ti4+ concentration of 0.5 M at room temperature to 100°C under a pressure of 1 atm. TiO2 precipitates with pure rutile phase having spherical shapes 200-400 nm in diameter formed between room temperature and 65°C, whereas TiO2 precipitates with anatase phase started to form at temperatures >65°C. Precipitates with pure anatase phase having irregular shapes 2-5 µm in size formed at 100°C. Possibly because of the crystallization of an unstable intermediate product, TiO(OH)2 , to TiO2 x H2 O during precipitation, crystalline and ultrafine TiO2 precipitates were formed in aqueous TiOCl2 solution without hydrolyzing directly to Ti(OH)4 . Also, formation of a stable TiO2 rutile phase between room temperature and 65°C was likely to occur slowly under these conditions, although TiO2 with rutile phase formed thermodynamically at higher temperatures. 相似文献
12.
Hidetoshi Miyazaki 《International Journal of Applied Ceramic Technology》2008,5(5):490-498
TiO2 (0–20 mol%)-3 mol% yttria-stabilized zirconia (3YSZ) ceramics were prepared by a solid-state reaction. With increasing TiO2 content in 3YSZ, the structure of the main phase changed from a monoclinic, tetragonal, and cubic mixture to a tetragonal single phase. Increasing TiO2 content in 3YSZ caused an increase in the average grain size of these ceramics. The thermal conductivity decreased from 4.1 to 2.1 at room temperature with an increase in the TiO2 content. The specific heat of non-TiO2 -doped 3YSZ was slightly larger than all the doped TiO2 –3YSZ at room temperature. When the TiO2 content was >8 mol% in 3YSZ, no abrupt expansion, shrinkage, or cracks were observed on heating and cooling these samples; thus, the thermal stability of 3YSZ was improved by TiO2 solid solution. The ionic conductivity of the samples decreased with increasing TiO2 solid solution. 相似文献
13.
The system HfO2 -TiO2 was studied in the 0 to 50 mol% TiO2 region using X-ray diffraction and thermal analysis. The monoclinic ( M ) ⇌ tetragonal ( T ) phase transition of HfO2 was found at 1750°± 20°C. The definite compound HfTiO4 melts incongruently at 1980°± 10°C, 53 mol% TiO2 . A metatectic at 2300°± 20°C, 35 mol% TiO2 was observed. The eutectoid decomposition of HfO2,ss ) ( T ) → HfO2,ss ( M ) + HfTiO3 4,ss ss occurred at 1570°± 20°C and 22.5 mol% TiO2 . The maximum solubility of TiO2 in HfO2,ss ,( M ) is 10 mol% at 1570°± 20°C and in HfO2,ss ( T ) is 30 mol% at 1980°± 10°C. On the HfO2 -rich side and in the 10 to 30 mol% TiO2 range a second monoclinic phase M of HfO2 ( M ) type was observed for samples cooled after a melting or an annealing above 1600°C. The phase relations of the complete phase diagram are given, using the data of Schevchenko et al. for the 50% to 100% TiO2 region, which are based on thermal analysis techniques. 相似文献
14.
A liquid phase in the Al2 O3 -1 mol% TiO2 -0.5 mol% NaO1/2 composition is confirmed at ±1300°C by an electrical conductivity measurement. The ease of the method led to a study of the Al2 O3 -2 mol% CuO-2 mol% TiO2 system and to the geologically important detection of eutectics (peritectics) in rock materials. 相似文献
15.
Ehrenfried Zschech Paris N. Kountouros Günter Petzow Peter Behrens Alex Lessmann Ronald Frahm 《Journal of the American Ceramic Society》1993,76(1):197-201
Valence state and site symmetry of Ti ions in TiO2 –Y2 O3 –ZrO2 powders with 2 mol% Y2 O3 and 5, 10, 15, and 20 mol% TiO2 , respectively, are studied by X-ray absorption near-edge spectroscopy (XANES). Tetravalent Zr4+ ions are replaced predominantly by Ti4+ ions. Within the solubility region of Ti ions, a subsequent displacement of Ti ions from the center of symmetry is observed with increasing TiO2 content in TiO2 –Y2 O3 -stabilized tetragonal ZrO2 polycrystals (Ti-Y-TZP) under investigation. This behavior cannot be interpreted with a random substitution of Ti4+ ions on Zr4+ lattice sites. On the contrary, this correlation between the TiO2 content in Ti-Y-TZP and the shift of Ti ions indicates an increasing interaction between the Ti ions with growing TiO2 content, caused by a subsequent clustering of Ti ions. 相似文献
16.
Michelle M. Hedges Michael J. Bannister Mary S. J. Gani 《Journal of the American Ceramic Society》1991,74(9):2318-2320
The two-phase field involves a ZrO2 -TiO2 solid solution containing no more than 4 mol% TiO2 , and a BaTiO3 -BaZrO3 solid solution containing a maximum of 75 mol% BaTiO3 . The field narrows above 1300°C, probably because of the intrusion of a liquid-phase field into the ternary, beginning near the BaO-TiO2 edge. 相似文献
17.
An addition of just 0.4 wt% Li2 O to (Ba0.6 Sr0.4 )TiO3 powder was able to reduce the sintering temperature to ≤900°C and produce ceramics with a relative density of 97%. Small amounts of two secondary phases were formed during this process: Li2 TiO3 and Ba2 TiO4 . The addition of Li2 O depresses the ferroelectric character of the (Ba0.6 Sr0.4 )TiO3 and, as a result, reduces the permittivity, improves the temperature coefficient of permittivity, and reduces the dielectric losses. The tunability shows no significant variation with Li2 O concentration and remains between 16.5% and 13.5%. A low-temperature sintering mechanism was proposed. The mechanism involves the intermediate formation of BaCO3 , its melting and the incorporation of Li+ into the BST. The sintering mechanism can be characterized as reactive liquid-phase sintering. 相似文献
18.
The system TiO2 -P2 O5 was investigated in the compositional range TiO2 .P2 O5 to 100% TiO2 . Two compounds exist, TiO2 .P2 O5 and 5TiO2 .-2P2 O5 . TiO2 .P2 O5 begins to lose P2 O5 at 1400°C. and both fusion and vaporization proceed rapidly at 1500°C. 5TiO2 .2P2 O6 melts congruently at 1260°± 3°C. to a glass which can be retained in substantial quantities at room temperature. Physical properties of certain compositions are described. 相似文献
19.
Chunzhong Li † Jinyi Han Zongtao Zhang Hongchen Gu 《Journal of the American Ceramic Society》1999,82(8):2044-2048
A process of coating Al2 O3 particles with TiO2 by hydrolysis of Ti(OC4 H9 )4 using chemical vapor deposition in a rotary reactor has been developed. The process resulted in (1) a coating film of TiO2 which was compact and uniform with the fraction of TiO2 being 0.1%–10.0% and (2) an amorphous TiO2 coating at a low reaction temperature converted to anatase at a reaction temperature higher than 673 K. 相似文献
20.
The Li2 O-TiO2 pseudobinary phase diagram was determined from 50 to 100 mol% TiO2 by DTA, microscopy, and X-ray analysis; Li2 Ti3 O7 effectively melts congruently at 1300° and decomposes eutectoidally at 940°C. A solid solution based on Li2 TlO3 from 50 to ∼65 mol% TiO3 was observed to exist at >930°C. A new metastable phase was discovered with a composition of ∼75 mol% TiO2 and with a hexagonal unit cell (8.78 by 69.86 × 10−1 nm). Discrepancies in the literature regarding some of these phase equilibria are reconciled. 相似文献