共查询到20条相似文献,搜索用时 62 毫秒
1.
Carlos E. Bamberger Tamara J. Havedock Otto C. Kopp† 《Journal of the American Ceramic Society》1994,77(6):1659-1661
The ternary system SrO-CeO2 -TiO2 was investigated using X-ray diffractometry. The formation of a new compound, Sr2 Ce2 Ti5 O16 , was established, and its compatibilities with SrO, SrCeO3 , and SrTiO3 were studied. The results revealed the existence of a series of compounds Sr6–12x Ce6x Ti5 O16 and solid solutions Sr2+n Ce2 Ti5+n O16+3n ( n ≤ 6). 相似文献
2.
Shara S. Shoup ‡ Carlos E. Bamberger § Richard G. Haire 《Journal of the American Ceramic Society》1996,79(6):1489-1493
The compounds SrPu2 Ti4 O12 , Pu2 Ti3 O8.79 , and Pu2 Ti2 O7 , where plutonium is in the (III) oxidation state, were prepared and identified via X-ray diffraction (XRD). The solid solubility limit of Pu2 Ti2 O7 in Ln2 Ti2 O7 (Ln = Gd, Er, or Lu) was also studied via XRD; it was determined that the solubility of Pu2 Ti2 O7 increased as the radius of the lanthanide ion in the host compound decreased. Attempts to synthesize Sr2 Pu2 Ti5 O16 and Sr2 Ce2–y Puy Ti5 O16 solid solutions, where plutonium is in the (IV) oxidation state, were unsuccessful. 相似文献
3.
Phase relations in the system BaO-TiO2 from 67 to 100 mol% TiO2 were investigated at 1200° to 1450°C in O2 . Data were obtained by microstructural, X-ray, and thermal analyses. The existence of the stable compounds Ba6 Ti17 O40 , Ba4 Ti13 O30 , BaTi4 O9 , and Ba2 Ti9 O20 was confirmed. The compound BaTi2 O5 is unstable and either forms as a reaction intermediate below the solidus or crystallizes from the melt. The compounds Ba6 Ti17 O40 and Ba4 Ti13 O30 decompose in peritectic reactions, and BaTiO3 and Ba6 Ti17 O40 react to form a eutectic. Special conditions are required for the formation of Ba2 Ti9 O20 , which decomposes in a peritectoid reaction at 1420°C. The new phase diagram is presented. 相似文献
4.
An investigation of the ternary systems BaO-TiO2 -SnO2 and BaO-TiO2 -ZrO2 led to the discovery of two new compounds belonging to the system BaO-TiO2 . These compounds, Ba2 Ti9 -O20 and Ba2 Ti9 O20 , are stabilized by minute additions of SnO2 or ZrO2 . The known compound BaTi2 O5 can be obtained only from the molten phase and decomposes below 1300°C. into Ba2 Ti5 O12 and BaTiO2 . In these systems no ternary compounds are found. The ternary phase diagrams can be divided into regions with high and low dielectric losses, which are in accordance with the phase relations. Tables with crystallographic data of the new compounds are included. 相似文献
5.
Sea-Fue Wang Chiang-Chuang Chung Chai-Hui Wang Jinn P. Chu 《Journal of the American Ceramic Society》2002,85(6):1619-1621
Preparation of dense and phase-pure Ba2 Ti9 O20 is generally difficult using solid-state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba2 Ti9 O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. In this study, the effects of B2 O3 on the densification, microstructural evolution, and phase stability of Ba2 Ti9 O20 were investigated. It was found that the densification of Ba2 Ti9 O20 sintered with B2 O3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid-state sintering became dominant because of the evaporation of B2 O3 . With the addition of 5 wt% B2 O3 , the ceramic yielded a pure Ba2 Ti9 O20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO2 or ZrO2 . The facilities of B2 O3 addition to the stability of Ba2 Ti9 O20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species. 相似文献
6.
Subsolidus phase relations in the system Na2 O-Bi2 O3 -TiO2 at 1000°C were investigated by solid-state reaction techniques and X-ray diffraction methods. Five ternary compounds were observed in the system: Na0.5 Bi4.5 Ti4 O15 ; Na0.5 Bi0.5 TiO3 ; a cubic pyrochlore solid solution composed of xNa2 O.25Bi2 O3 .(75−;x) TiO2 where x is 2.5 to 3.75; a new compound Na0.5 Bi8.5 Ti7 O27 indexed with the orthorhombic cell of a = 5.45, b = 5.42, and c = 36.8 Å; and an unidentified phase with the probable composition NaBiTi6 O14 . 相似文献
7.
Shara S. Shoup Tamara J. Haverlock Carlos E. Bamberger 《Journal of the American Ceramic Society》1995,78(5):1261-1264
A region of selected SrO-LnO1.5 -TiO2 (Ln = La, Ce, Pr, or Nd) systems was studied experimentally using X-ray diffractometry (XRD). A series of solid solutions with composition Sr4 x Ln2 x/ 3 Ti4 O12 having tetragonally distorted per-ovskite structures was found to exist along the tie line connecting SrTiO3 and Ln2 Ti3 O9 . Reactions of SrLn2 Ti4 O12 , representative compounds of the series, with SrO were also studied. Additionally, the solubility of TiO2 in Ln2 O3 -(3TiO2- m (Ln = La, Pr, or Nd) at 1300°C was investigated using XRD. 相似文献
8.
TAKESHI KIKUCHT 《Journal of the American Ceramic Society》1977,60(3-4):148-150
The subsolidus phase equilibria in the system Bi2 O3 -TiO2 -Nb2 O5 at 1100°C were determined by solid-state reaction techniques and X-ray powder diffraction methods. The system was found to contain 4 ternary compounds, i.e. Bi3 TiNbO9 , Bi7 Ti4 NbO21 , a cubic pyrochlore solid solution having a compositional range of 3Bi2 O3 · x TiO2 (7– x )Nb2 O5 where x ranges from 2.3 to 6.75, and an unidentified phase, 4Bi2 O3 ·11TiO2 ·5Nb2 O5 . 相似文献
9.
Jiaqing Yu Hangwei Zhao Jiasheng Wang Fei Xia 《Journal of the American Ceramic Society》1994,77(4):1052-1056
High-performance Ba2 Ti9 O20 ceramics are attracting great attention, but their formation mechanism still is somewhat unclear. The present investigation shows that the formation of Ba2 Ti9 O20 can be promoted strikingly by the participation of Bi2 O3 and Al2 O3 . The effect of Bi2 O3 on the formation of Ba2 Ti9 O20 is attributed to the fact that migration of the involved reactants is accelerated by liquid which forms from the melting of Bi2 O3 above 830°C. This migration, however, is not the only rate-limiting factor. A high potential-energy barrier, resulting from stress that arises along the crystal-structured layers, also heavily restricts the formation of Ba2 Ti9 O20 . The participation of Al2 O3 , on the other hand, can reduce the height of this potential-energy barrier and effectively improve the kinetics of the formation of Ba2 Ti9 O20 by causing the formation of BaAI2 Ti6 O16 crystals; these crystals intergrow with Ba2 Ti9 O20 crystals and result in decreased stress. 相似文献
10.
Near-field scanning microwave microscopy was applied to investigate the dielectric properties and microstructure in a polycrystalline LaAlO3 –TiO2 diffusion couple, which included three regions containing different phases and microstructures. Relatively low (La2 Ti4 Al18 O38 ), high (α-La2/3 TiO3 ), and intermediate (La4 Ti9 O24 ) dielectric constant phases were distinguished at the inter-diffusion interface in optical, backscattered electron scanning electron microscopy, and scanning microwave microscopy (SMM) images. The relative ranking of dielectric constants based on SMM examination was as follows: TiO2 >α-La2/3 TiO3 >La4 Ti9 O24 >LaAlO3 >La2 Ti4 Al18 O38 . La2/3 TiO3 and LaAlO3 will form solid solutions in the LaAlO3 -rich region. The reaction paths leading to phase development are discussed. 相似文献
11.
Darko Makovec Irena Priboic Zoran Samardija Miha Drofenik 《Journal of the American Ceramic Society》2001,84(11):2702-2704
The solid solubility of the aliovalent dopants Fe3+ and Nb5+ in the BaBi4 Ti4 O15 compound, a member of the family of Aurivillius bismuth-based layer-structure perovskites, has been studied using quantitative wavelength-dispersive spectroscopic microanalysis (SEM/EPMA) in combination with X-ray powder diffractometry (XRPD). The samples with nominal (starting) compositions corresponding to the chemical formulas BaBi4 Ti4–4 X Fe4 X O15 and BaBi4 Ti4–4 X Nb4 X O15 were prepared by hot forging a mixture of BaTiO3 and Bi4 Ti3 O12 with additions of Fe2 O3 or Nb2 O5 followed by a long annealing at 1100°C. The study showed that an excess charge introduced into the structure by the substitution of Ti4+ ions with aliovalent dopants was preferentially compensated by a change in the ratio of Ba2+ to Bi3+ ions in the host structure according to the general formulas of the solid solutions Ba1–4 X Bi4+4 X Ti4–4 X Fe' 4 X O15 and Ba1+4 X Bi4–4 X Ti4–4 X Nb· 4 X O15 . 相似文献
12.
Marko Udovic Matjaz Valant Botjan Janar Danilo Suvorov Anton Meden Anton Koevar 《Journal of the American Ceramic Society》2006,89(11):3462-3469
Using X-ray diffraction analysis and scanning electron microscopy it was revealed that in an atmosphere of flowing oxygen in the temperature range 700°–800°C, three new compounds are formed in the Bi2 O3 –TiO2 –TeO2 pseudoternary system. These compounds are Bi2 Ti3 TeO12 , Bi2 TiTeO8 , and Bi6 Ti5 TeO22 , and all the compounds include Te6+ . All three crystal structures were solved and refined using X-ray powder diffraction data. Based on the results of the phase formation, a solid-state compatibility diagram is proposed. 相似文献
13.
Hong-Wen Wang 《Journal of the American Ceramic Society》1995,78(4):1134-1135
in a recent article of the Journal , Yu et al .1 reported their experimental results on the effect of Al2 O3 and Bi2 O3 on the formation mechanism of Sn-doped Ba2 Ti9 O20 . They claimed that both Al2 O3 and Bi2 O3 can dramatically assist the formation of Sn-doped Ba2 Ti9 O20 but are based on different mechanisms. They concluded that first, Bi2 O3 melts above 830°C and accelerates the migration of the involved reactants to form Ba2 Ti9 O20 ; second, Al2 O3 can reduce the height of the potential energy barrier of the formation of Ba2 Ti9 O20 due to the intergrowth of BaAl2 Ti6 O16 phase. They explained their results from a point of view that the formation of Ba2 Ti9 O20 is controlled by (1) the migration of reactants to the interfaces and (2) the height of the potential-energy barrier of the reaction at the interfaces. However, based on their results, we feel their conclusions are incautious and may be misleading, as will be discussed later. 相似文献
14.
Ferroelectric thin films of bismuth-containing layered perovskite PbBi2 Nb2 O9 have been prepared by a metalorganic decomposition (MOD) method. Random and highly c-oriented films of the same starting composition have been obtained under different intermediate- and high-temperature heat treatments. A comparison of their crystallization and properties with those of Bi4 Ti3 O12 films reveals similar trends that are common to bismuth-containing Aurivillius compounds. Heterogeneous nucleation of the perovskite phase either on the pyrochlore (444) plane because of lattice matching or on the substrate surface because of lower interfacial energy is proposed as the cause of orientation selection during crystallization. The different thickness of the pseudoperovskite subunits in these layered compounds may be responsible for the systematic difference in the anisotropic ferroelectric properties. Smaller polarization and higher coercive field are expected for PbBi2 Nb2 O9 , which has thinner pseudoperovskite units than Bi4 Ti3 O12 . 相似文献
15.
Ahmed G. Solomah Reinhard Odoj Christoph Freiburg 《Journal of the American Ceramic Society》1983,66(10):c182-c183
A new identification and indexing for the phase BaAl2 Ti5 O14 were accomplished using an X-ray diffraction technique. The new lattice parameters for the tetragonal lattice structure are: a0 =9.990 × 10-10 m and c0 =12.264 × 10-10 m, with a corresponding volume 1.224 × 10-27 m3 . The data provided by the Joint Committee on Powder Diffraction Standards are inconsistent both in lattice parameter values and Miller indices. The X-ray powder diffraction pattern of BaAl2 Ti5 O14 was indexed using the LSUCR (least-squares unit cell refinement) computer program. 相似文献
16.
The system TiO2 -Bi2 Ti4 O11 was examined by Raman spectroscopy and X-ray diffraction to determine whether TiO2 is soluble in Bi2 Ti4 O11 . The Raman spectral data obtained from preparations made at ∼ 1050°C and cooled to room temperature led us to conclude that TiO2 is not soluble in the "high-temperature" form of Bi2 Ti4 O11 . It was also found that extensive grinding of the phase identified as the "high-temperature" form converts it to the "low-temperature" form, stable below 250°C. 相似文献
17.
Above 755°C, compounds along the spinel join LiFe5 O8 -Li4 Ti5 O12 form a complete solid solution and below that temperature a two-phase region separates the ordered LiFe5 O8 and the disordered spinel phase. At 800° and 900°C, cubic LiFeO2 ( ss ) and monoclinic Liz Ti03 ( ss ) exist on the monoxide join LiFeO2 -Li2 TiO3 . The distributions of cations in both the spinel and monoxide structures were calculated as a function of equilibrium temperature and composition. Sub-solidus equilibria in the system Li2 O-Fe2 O3 -TiO2 at 800° and 900°C were determined for compositions containing ∼50 mol% Li2 O. 相似文献
18.
The reoxidation process in highly Ce3+ -doped BaTiO3 ceramics was studied using TEM. Samples of two different types of solid solutions, Ba1−X Ce3+ X Ti1−X/4 ( V Ti ) X/4 O3 and Ba1−X Ce3+ X Ti4+ 1− X Ti3+ X O3 , were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce3+ and Ti3+ , fluorite CeO2 and monoclinic Ba6 Ti17 O40 phases were precipitated in the perovskite matrix. In Ba1−X Ce3+ X Ti1−X /4( V Ti )X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba1−X Ce3+ X Ti4+ 1−X Ti3+ X O3 solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed. 相似文献
19.
Modification of the microwave dielectric properties in Ba6−3 x Nd8+2 x Ti18 O54 ( x = 0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near-zero temperature coefficient combined with high Qf values were obtained in modified Ba6−3 x Nd8+2 x Ti18 O54 solid solutions where an enlarged solid solution limit of Bi in Ba6−3 x Nd8+2 x Ti18 O54 was observed. Excellent microwave dielectric characteristics (ɛ= 105, Qf = 4110 GHz, and very low τf ) were achieved in the composition Ba6−3 x (Nd0.7 Bi0.18 Sm0.12 )8+2 x Ti18 O54 . 相似文献
20.
Hiroyuki Ikawa Hiromasa Shimojima Kazuyori Urabe Osamu Fukunaga 《Journal of the American Ceramic Society》1991,74(8):1899-1904
Axial and dilatometric thermal expansions and phase transformations were studied for solid solutions having the α-PbO2 structure in the ZrTiO4 —In2 O3 —M2 O5 (M = Sb, Ta) system with nominal formulas of Zr x Ti y In z Sb z O4 and Zr x Ti y In z Ta z O4 where x + y + 2 z = 2. With increased substitution of z , the cell volume increased, the difference in the b parameters at room temperature between those quenched from 1400° and 1000°C decreased, and the thermal expansion decreased. The axial thermal expansion of ZrTi y In z · Ta z O4 with z = 0.3 was almost identical with that of HfTiO4 , and those with z = 0.4 and z = 0.45 were smaller than that of HfTiO4 . Unit-cell volumes of these compound were compared with those of single oxides to make it clear that the unit-cell volume of ZrTiO4 was small anomalously and to distinguish the normal and abnormal substitution systems. These results were explained by the working hypothesis proposed for these compounds. 相似文献