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1.
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
2.
Prem Prakash Ashish Garg Mukesh Kumar Roy Harish Chandra Verma 《Journal of the American Ceramic Society》2007,90(4):1295-1298
In this study, we report on the synthesis of nanopowders of ferroelectric Bi3.5 Nd0.5 Ti3 O12 ceramic at temperatures below 500°C via a simple chemical method using citric acid as a solvent. The calcined powders were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Heating the as-dried powders in air first leads to crystallization of the Bi2 Ti2 O7 phase at ∼310°C, followed by crystallization of the perovskite Nd-doped Bi4 Ti3 O12 phase at ∼490°C as suggested by the peaks in the DSC analysis and confirmed by the evolution of phases in XRD patterns of the powders calcined at various temperatures. TEM of particles calcined at 550°C for 1 h in air showed an average particle size of 50–60 nm. The temperature dependence of capacitance of nanopowders calcined at 700°C for 1 h in air showed a Curie temperature of ∼615°C evincing a ferroelectric transition. 相似文献
3.
Nong M. Hwang Robert S. Roth Claudia J. Rawn 《Journal of the American Ceramic Society》1990,73(8):2531-2533
The phase equilibria of the systems SrO-CuO and SrO-1/2Bi2 O3 were studied by X-ray diffraction analysis of quenched powder samples. The compounds SrCuO2 and Sr2 CuO3 melt incongruently at 1085° and 1225°C, respectively. The newly found compound Sr6 Bi2 O9 decomposes at 965°C into SrO and Sr3 Bi2 O6 melts incongruently into SrO and liquid at 1210°C. SrBi2 O4 undergoes a phase transition at ∼825°C, and although both are nonstoichiometric, the low-temperature phase is slightly poorer in SrO with 33.5 mol% SrO than the high-temperature phase. 相似文献
4.
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
5.
Wei Zhao Heping Zhou Yongke Yan Dan Liu 《Journal of the American Ceramic Society》2008,91(4):1322-1325
Plate-like Na0.5 Bi0.5 TiO3 (NBT) particles with perovskite structure were synthesized by topochemical microcrystal conversion from plate-like particles of layer-structured Na0.5 Bi4.5 Ti4 O15 (NBIT) at 950°C in NaCl molten salt. As the precursors of NBT, plate-like NBIT particles were first synthesized by molten salt process by the reaction of Bi4 Ti3 O12 , Na2 CO3 , and TiO2 . After the topochemical reactions, layer-structured NBIT particles were transformed to the perovskite NBT platelets. NBT particles with a thickness of approximately 0.5 μm and a length of 10–15 μm retained the morphology feature of the precursor. High-aspect-ratio NBT platelets are suitable templates to obtain textured ceramics (especially NBT-based ceramics) by (reactive) template grain growth process. 相似文献
6.
Carmen García-Rosales Horst A. Schulze Aristides Naoumidis Hubertus Nickel 《Journal of the American Ceramic Society》1993,76(11):2869-2878
The quasi-ternary system Cr─Mn─Ti oxide was investigated at 1000°C under oxygen partial pressures ranging from 0.21 bar to 10-21 bar (1 bar = 105 Pa). X-ray diffraction analysis was used to identify phases and determine lattice parameters. The positions of phase boundaries as a function of oxygen partial pressure were measured using the emf method. The spinel MnCr2 O4 may be regarded as the most interesting compound in this system. Part of the chromium can be replaced by trivalent titanium at low oxygen partial pressures and by trivalent manganese at high pressures, and the formation of a limited solid solution with the spinel Mn2 TiO4 is possible in all cases. As a result, a coherent single-phase spinel region exists over the entire oxygen partial pressure range at 1000°C. 相似文献
7.
Michael K. Cinibulk Geoff E. Fair Ronald J. Kerans 《Journal of the American Ceramic Society》2008,91(7):2290-2297
The stability of lanthanum orthophosphate (LaPO4 ) on SiC was investigated using a LaPO4 -coated SiC fiber at 1200°–1400°C at low oxygen partial pressures. A critical oxygen partial pressure exists below which LaPO4 is reduced in the presence of SiC and reacts to form La2 O3 or La2 Si2 O7 and SiO2 as the solid reaction products. The critical oxygen partial pressure increases from ∼0.5 Pa at 1200°C to ∼50 Pa at 1400°C. Above the critical oxygen partial pressure, a thin SiO2 film, which acts as a reaction barrier, exists between the SiC fiber and the LaPO4 coating. Continuous LaPO4 coatings and high strengths were obtained for coated fibers that were heated at or below 1300°C and just above the critical oxygen partial pressure for each temperature. At temperatures above 1300°C, the thin LaPO4 coating becomes morphologically unstable due to free-energy minimization as the grain size reaches the coating thickness, which allows the SiO2 oxidation product to penetrate the coating. 相似文献
8.
ROBERT S. ROTH JOSEPH J. RITTER HARRY S. PARKER DENNIS B. MINOR 《Journal of the American Ceramic Society》1986,69(12):858-862
Only ZrO2 was found to stabilize the phase previously reported as "Ba2 Ti5 O12 ." A metastable phase corresponding to this compound was found to form between 650° and 675°C from hydrolyzed ethoxide precursors. The stability was increased to ∼850°C by the addition of 1 to 2 mol% Nb2 O5 to the precursor solutions. Addition of 5 mol% SnO2 failed to yield appreciable amounts of this phase in solid-state preparations, contrary to the previous report. Addition of 8 mol% ZrO2 , however, did produce the desired phase as reported, both with and without additional Nb2 O5 , apparently stable to >1300°C. Small single crystals, picked from a ZrO2 -stabilized specimen with 1 mol% Nb2 O5 , showed the compound Ba2 Ti5- x Zrx O12 to be a 10-layer structure, triclinic, pseudo-orthorhombic with A-centered symmetry and a =9.941(5), b = 11.482(4), c = 23.528 (10) × 10–1 nm. The corresponding reduced triclinic unit cell has a = 9.941, b = 11.482, c = 13.090 × 10–1 nm, α= 116.01°, β= 90.0°, γ= 90.0°. 相似文献
9.
BaTi4 O9 and Ba2 Ti9 O20 precursors were prepared via a sol–gel method, using ethylenediaminetetraacetic acid as a chelating agent. The sol–gel precursors were heated at 700°–1200°C in air, and X-ray diffractometry (XRD) was used to determine the phase transformations as a function of temperature. Single-phase BaTi4 O9 could not be obtained, even after heating the precursors at 1200°C for 2 h, whereas single-phase Ba2 Ti9 O20 (as determined via XRD) was obtained at 1200°C for 2 h. Details of the synthesis and characterization of the resultant products have been given. 相似文献
10.
Robert S. Roth Nong M. Hwang Claudia J. Rawn Benjamin P. Burton Joseph J. Ritter 《Journal of the American Ceramic Society》1991,74(9):2148-2151
New data are presented on the phase equilibria of the binary systems CaO-CuO and CaO-Bi2 O3 . Corrected compositions are reported for Ca.Bi6 O13 and Ca2 Bi2 O5 and a new metastable high-temperature phase is reported for a composition near Ca6 Bi7 O16.5 . The composition and decomposition temperatures for Ca1–x .CuO2 are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively. 相似文献
11.
Sintering and Dielectric Characterization of Pseudoternary Compounds from the Bi2 O3 –TiO2 –TeO2 System
Using X-ray diffraction analysis, scanning electron microscopy, thermogravimetry, and measurements of the dielectric properties up to the MW frequency range, the characterization of Bi2 Ti3 TeO12 , Bi2 TiTeO8 , and Bi6 Ti5 TeO22 compounds, which all include Te6+ , was performed. As the processes of Te6+ reduction and the evaporation of TeO2 -containing species contribute to the presence of secondary phases, the preparation of single-phase ceramics is rather difficult. To minimize the amount of secondary phases during the firing process, the pellets were muffled in a corresponding compound and then fired in an autoclave furnace under 10 bars of oxygen pressure. By sintering the Bi2 Ti3 TeO12 , Bi2 TiTeO8 , and Bi6 Ti5 TeO22 between 840° and 1010°C, ceramics with ɛr ranging from 36 to 350, Q × f values from 220 to 12 500 GHz, and τf from +41 to +2600 ppm/K were obtained. 相似文献
12.
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
13.
La0.8 Sr0.2 Cr0.9 Ti0.1 O3 perovskite has been designed as an interconnect material in high-temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La0.8 Sr0.2 Cr0.9 Ti0.1 O3 shows a single phase with a hexagonal unit cell of a = 5.459(1) Å, c = 13.507(2) Å, Z = 6 and a space group of R -3 C . Average linear thermal expansion coefficients of this material in the temperature range from 50° to 1000°C were 10.4 × 10−6 /°C in air, 10.5 × 10−6 /°C under a He–H2 atmosphere (oxygen partial pressure of 4 × 10−15 atm at 1000°C), and 10.9 × 10−6 /°C in a H2 atmosphere (oxygen partial pressure of 4 × 10−19 atm at 1000°C). La0.8 Sr0.2 Cr0.9 Ti0.1 O3 perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air-sintering problem to be solved in using this material as an SOFC interconnect. 相似文献
14.
The 1200°C. isotherm in the system Fe-Ti-O has been studied by equilibrating mixtures of iron oxide (Fe2 O3 ) and titanium oxide (TiO2 ) with atmospheres of controlled oxygen partial pressure. These atmospheresmnsisted of CO2 , air, oxygen, mixtures of CO2 and H2 , and mixtures of CO2 and CO. The resulting oxide mixtures were examined at room temperature by chemical analysis and by X-ray diffraction. The stability regions of the α-oxides (Fem Ti2-m O3 ), of the spinels, (Fen Ti3-n O4 ), and of the orthorhombic oxides (Fep Ti3-p O5 )were determined. Some nonstoichiometry occurs in the spinels and in the α-oxides. The oxygen partial pressures at which spinel is reduced to (iron +α-oxides) and at which α-oxide (ilmenite) is reduced to (iron + orthorhombic oxide) were determined as 2.1 × 10−13 and 9.3 × 10−14 atm., respectively. The orthorhombic solid solution series extends over the whole range of oxygen partial pressures studied. 相似文献
15.
Two cubic pyrochlore phases exist in the system ZnO–Bi2 O3 –Sb2 O5 . Neither has the supposed "ideal" stoichiometry, Zn2 Bi3 Sb3 O14 . One, P 1 , is a solid solution phase, Zn2+ x Bi2.96−( x − y ) Sb3.04− y O14.04+δ where 0< x <0.13(1), 0< y <0.017(2) and a =10.4285(9)−10.451(1) Å. The other, P 2 , is a line phase, Zn2 Bi3.08 Sb2.92 O13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P 1 and P 2 in the ZnO–Bi2 O3 –Sb2 O5 phase diagram have been determined. 相似文献
16.
The phase relationships in the system ZrO2 -TiO2 near the compound ZrTiO4 have been clarified through an experimental study involving the characterization of both single-crystal and powder specimens, the latter prepared through conventional solid-state reaction and also by low-temperature co-precipitation methods. Zr1+ x Ti1- x O4 (1/10 > x >-1/6), having the α-PbO2 -type structure, is found to transform on cooling between ∼1100° and ∼1150°C. Below this temperature there is an unusual, continuous phase transition leading to the formation of the stable low-temperature phase ZrTi2 O6 . Low-level doping with Y2 O3 was found to enhance apparent cation ordering in intermediate compositions in the temperature range just below the phase transition. 相似文献
17.
Noboru Tohge Satoshi Takahashi Tsutomu Minami 《Journal of the American Ceramic Society》1991,74(1):67-71
Ferroelectric films, PbZr x Ti1− x O3 ( x = 0 to 0.6), have been prepared from corresponding metal alkoxides partially stabilized with acetylacetone through the sol-gel process. The films dip-coated in an ambient atmosphere were heat-treated at 400°C for decomposition of residual organics and then at temperatures between 500° and 700°C for crystallization of the films. The perovskite phase precipitated at temperatures above 560°C, accompanied by an increase in dielectric constant. The dielectric constant of the films, which was comparable with that of sintered bodies, showed a maximum (∼620) at around x = 0.52 in PbZr x Ti1− x O3 . These films showed D – E hysteresis, with slightly higher values of coercive field, compared with those of sintered bodies. 相似文献
18.
The subsolidus phase relations in the entire system ZrO2 -Y2 O3 were established using DTA, expansion measurements, and room- and high-temperature X-ray diffraction. Three eutectoid reactions were found in the system: ( a ) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y2 O3 and ∼490°C, ( b ) cubic zirconia solid solutiow→δ-phase Y4 Zr3 O12 +hexagonalphase Y6 ZrO11 at 45 mol% Y2 O3 and ∼1325°±25°C, and ( c ) yttria C -type solid solution→wcubic zirconia solid solution+ hexagonal phase Y6 ZrO11 at ∼72 mol% Y2 O3 and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y2 O3 with ideal formula Y4 Zr3 O12 , and another, a new hexagonal phase, at 75 mol% Y2 O3 with formula Y6 ZrO11 . They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C -type solid solution, respectively. The extent of the cubic zirconia and yttria C -type solid solution fields was also redetermined. By incorporating the known tetragonal-cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO2 -Y2 O3 . 相似文献
19.
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
20.
Myeong-Heon Um Chul-Tae Lee Hidehiro Kumazawa 《Journal of the American Ceramic Society》2001,84(5):1181-1183
TiO2 fibers were formed by thermal treatment of layered H2 Ti4 O9 (hydrous titanium dioxide) and KHTi4 O9 synthesized by ion-exchange reactions. The calcination of the former at 900° and 1050°C for 3 h yielded TiO2 fibers with anatase and rutile phases, whose length and diameter were 15–20 and 2–5 μm and 10–15 and 3–5 μm, respectively. The thermal treatment of the latter at temperatures of 250° to 500°C yielded pure K2 Ti8 O17 , which tended to decompose to K2 Ti6 O13 and TiO2 at temperatures >600°C. At 1050°C, K2 Ti6 O13 phase was formed with rutile TiO2 fibers, whose length and diameter were 10–20 and 1–3 μm, respectively. 相似文献