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1.
Phase relations at 1500°C in the ternary system ZrO2–Gd2O3–TiO2 have been determined by the powder X-ray diffraction of samples prepared by standard solid state reaction. A large area of this ternary oxide system centered on the Gd2Ti2O7–Gd2Zr2O7 join was shown to exhibit the pyrochlore and defect fluorite structures. The pyrochlore structure was observed for stoichiometries as far from the ideal M4O7 as M4O6.7 and M4O7.4, although the degree of disorder seemed much higher at these stoichiometries. On further deviation from the ideal M4O7 stoichiometry a smooth transition to fluorite average structure was observed for Zr-rich compositions. None of the other binary phases were observed to show significant extent of solid solution into the ternary region.  相似文献   

2.
The phase relations of the system Cr2O3TiO2 were determined at temperatures between 1400 and 1765°C in air. Discrete homologous series of Cr2Tin?2O2n?1, with n = 6, 7, 8, were found to be stable as single phases in the range of certain temperatures, while a continuous solid solution existed in the composition of n > 8 below 1425°C. This presence and its stable region of a new compound of Cr2TiO5 corresponding to n = 3 are revealed in the present paper. Cr2Ti2O7, the so-called E phase, existed in wide homogeneity range, corresponding to the composition of approximately 3 < n < 5. High-temperature phases (called n and n′ phases in the present work) existed above 1425°C and seemed to be closely related to each other from the viewpoint of the structure except that some X-ray diffraction lines of n phase were strongly diffused. Both rutile and chromia had limited solid solubilities. In the present paper, phase relations between Cr2O3 and TiO2 are summarized in a phase diagram.  相似文献   

3.
Subsolidus phase equilibria and crystal chemistry were studied for the La2O3-MgO-TiO2 system and for the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3 in the quaternary La2O3-CaO-MgO-TiO2 system. Dielectric properties (relative permittivity and temperature coefficient of resonant frequency, τf) were measured at 5-10 GHz and mapped onto the phase equilibria relations to reveal the compositions of temperature-stable (τf=0) compounds and mixtures. Phase equilibria relations were obtained by X-ray powder diffraction analysis of approximately 80 specimens prepared by solid-state reactions in air at ∼1450°C. Six ternary phases were found to form in the La2O3-MgO-TiO2 system, including the three previously reported compounds LaMg1/2Ti1/2O3, La5Mg0.5Ti3.5O15, and “La6MgTi4O18”; and the new phases La10MgTi9O34, La9Mg0.5Ti8.5O31, and a perovskite-type solid solution (1−x)LaMg1/2Ti1/2O3-xLa2/3TiO3 (0?x?0.5). The phase previously reported as “La6MgTi4O18” was found to form off-composition, apparently as a point compound, at La6Mg0.913Ti4.04O18. Indexed experimental X-ray powder diffraction patterns are given for LaMg1/2Ti1/2O3, La5Mg0.5Ti3.5O15, La6Mg0.913Ti4.04O18, La10MgTi9O34, and La9Mg0.5Ti8.5O31. LaMg1/2Ti1/2O3 exhibits a slightly distorted perovskite structure with ordered B-cations (P21/n; a=5.5608(2) Å, b=5.5749(3) Å, c=7.8610(5) Å, β=90.034(4)°). La5Mg0.5Ti3.5O15 (Pm1; a=5.5639(1), c=10.9928(5) Å) and La6Mg0.913Ti4.04O18 (R3m; a=5.5665(1), c=39.7354(9) Å) are n=5 and n=6 members, respectively, of the (111) perovskite-slab series AnBn−1O3n. The new phases La10MgTi9O34 (a=5.5411(2), b=31.3039(9), c=3.9167(1) Å) and La9Mg0.5Ti8.5O31 (a=5.5431(2), b=57.055(1), c=3.9123(1) Å) are n=5 and n=4.5 members, respectively, of the (110) perovskite-slab series AnBnO3n+2, which exhibit orthorhombic subcells; electron diffraction revealed monoclinic superlattices with doubled c-parameters for both compounds. Extensive perovskite-type solid solutions form in the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3. The La2O3-MgO-TiO2 system contains two regions of temperature-stable (τf=0) compositions. The quaternary La2O3-CaO-MgO-TiO2 system contains an extensive single-phase perovskite-type volume through which passes a surface of temperature-stable compositions with permittivities projected to be in the 40-50 range. Traces of this surface occur as lines of τf=0 perovskite-type phases in the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3.  相似文献   

4.
Gravimetry in combination with X-ray phase analysis, X-ray crystallography, and X-ray densitometry were used to determine the contents of V5+, V4+, and Ti4+ ions and vacancies in solid solutions formed by the reaction of V2O5 with TiO2 in air at atmospheric pressure.  相似文献   

5.
DTA, TG, XRD and IR methods were used to study the formation of solid solutions in the selected subsolidus range of the PbZrO3-K0.5Bi0.5TiO3 system by heating mixtures prepared using oxide substrates, i.e. PbO, Bi2O3, ZrO2, TiO2 and K2CO3. It was found that solid solutions are formed in the reaction of PbO and ZrO2 with intermediate compound, i.e. K0.5Bi0.5TiO3. PbZrO3 was not found to be formed as an intermediate phase. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

6.
Reduction of the titanium-niobium oxides follows a common pattern. TiO2 is eliminated, to form a new phase richer in titanium than the original compound, and Nb(iv) replaces Ti(iv) in the original block structure, which is thereby enriched in niobium. With TiNb2O7, the second phase is a TiO2NbO2 solid solution, with the rutile structure, initially with a high titanium content, in equilibrium with a solid solution of composition Me3O7, isostructural with TiNb2O7. At log pO2 (atm) about ?9.0 this reaches the limiting composition Ti0.72Nb2.28O7, in equilibrium with Ti0.56Nb0.44O2. The Me3O7 block structure then transforms into the Me12O29 block structure (Ti2Nb10O29Nb12O29 solid solution), which rapidly increases in niobium content as reduction continues. Reduction of Ti2Nb10O29 at oxygen fugacities above log pO2 (atm) = ?9.0 forms the Me3O7 phase as the titanium-rich phase. At log pO2 = ?9.0, and a composition about Ti1.6Nb10.4O29, the rutile solid solution takes over as second phase. The niobium/titanium ratio in both phases rises as reduction proceeds, and the last vestiges of the Me12O29 phase, in equilibrium with the final product, Ti0.17Nb0.67O2, are almost denuded of titanium.  相似文献   

7.
A systematic study of compound and solid-solution formation in the system Li2ONb2O5TiO2 has been made. Several solid-solution series, based on LiNbO3, LiNb3O8, Li2Nb28O71, Li2TiO3, phase M, Li2Ti3O7, and TiO2, have been characterized. In all cases, the principal solid-solution mechanism appears to involve stoichiometric formulae with constant overall cation content. One new phase, of approximate formula Li13TiNb5O21, has been prepared. A subsolidus phase diagram for the ternary system is presented.  相似文献   

8.
Nanocrystalline lanthanum zirconate La2Zr2O7 was synthesized by the solid-phase method using preliminary mechanical activation of a La2O3 and ZrO2 mixture. Processes occurring during heating the mixture of mechanoactivated lanthanum and zirconium oxides were studied using the X-ray phase analysis, IR spectroscopy, and complex thermal analysis. Synthesized lanthanum zirconate was characterized by the X-ray phase analysis and transmission electron microscopy methods.  相似文献   

9.
Thin crystals of La2O3, LaAlO3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1×1016 ions cm−2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 647 K for LaAlO3, 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for Al2O3 and TiO2, are discussed with reference to the melting points for the La2O3-Al2O3 and La2O3-TiO2 systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between Tc and melting temperature (Tm) in the two systems. More complex relationships exist between Tc and crystal structure, with the stoichiometric perovskite LaAlO3 being the most resistant to amorphisation.  相似文献   

10.
The subsolidus phase equilibrium relations in the system BaO.TiO2.Al2O3 have been investigated using conventional solid state reaction techniques and X-ray powder diffraction. The existence of three known ternary compounds, BaTi5Al2O14, BaTiAl6O12, and Ba3TiAl10O20, was confirmed and their stability relations were studied. Various tie-lines existing between the ternary compounds and the binary titanates and aluminates of barium were established and a subsolidus phase diagram showing the phase assemblages compatible at 1200°C is presented.  相似文献   

11.
Compounds Ce2TiO5, Ce2Ti2O7, and Ce4Ti9O24 were prepared by heating appropriate mixtures of solids containing Ce4+ and Ti3+ or Ti which were placed in a platinum-silica-ampoule combination at T = 1250°C (3d) under vacuum. The new compounds were characterized by powder patterns. We obtained Ce2TiO5 which is isotypic to La2TiO5 and crystallizes in the Y2TiO5-type (space group Pnma) with a = 10.877(6) Å, b = 3.893(1) Å, c = 11.389(8) Å, Z = 4. Ce2Ti2O7 is isotypic to La2Ti2O7 and crystallizes in the monoclinic Ca2Nb2O7 type (space group P 21) with a = 7.776(6) Å, b = 5.515(4) Å, c = 12.999(6) Å, β = 98.36(5), Z = 4. The compound Ce4Ti9O24 crystallizes orthorhombic with a = 14.082(4) Å, b = 35.419(8) Å, c = 14.516(4) Å, Z = 16. The new cerium titanate Ce4Ti9O24 is isotypic to Nd4Ti9O24 (space group Fddd (No. 70)) which represents a novel type of structure.  相似文献   

12.
How 2D Ti3C2 enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti3C2, rather than 2D Ti3C2 itself, that play the role of co-catalyst for La2Ti2O7/Ti3C2 (LTC) composites during the photocatalytic reaction. After modification of Ti3C2 derivatives, the photocatalytic efficiency of La2Ti2O7 is enhanced 16 times over pure La2Ti2O7. Solid-state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti3C2 and LTC composites. The GQDs are formed during the chemical change from Ti3AlC2 to Ti3C2 via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp2 π-conjugation GQDs. 2D Ti3C2 is completely oxidized to COx modified TiOx species, causing Ti3C2 to lose its electrical conductivity and the role as co-catalyst. GQDs largely suppress the photogenerated charge recombination of La2Ti2O7, as revealed by the photoluminescence (PL) and transient photocurrent.  相似文献   

13.
The phase relations in the system In2O3–TiO2–MgO at 1100 and 1350°C are determined by a classical quenching method. In this system, there are four pseudobinary compounds, In2TiO5, MgTi2O5 (pseudobrookite type), MgTiO3 (ilmenite type), and Mg2TiO4 (spinel type) at 1100°C. At 1350°C, in addition to these compounds there exist a spinel-type solid solution Mg2−xIn2xTi1−xO4 (0≤x≤1) and a compound In6Ti6MgO22 with lattice constants a=5.9236(7) Å, b=3.3862(4) Å, c=6.3609(7) Å, β=108.15(1)°, and q=0.369, which is isostructural with the monoclinic In3Ti2FeO10 in the system In2O3–TiO2–MgO. The relation between the lattice constants of the spinel phase and the composition nearly satisfies Vegard's law. In6Ti6MgO22 extends a solid solution range to In20Ti17Mg3O67 with lattice constants of a=5.9230(5) Å, b=3.3823(3) Å, c=6.3698(6) Å, β=108.10(5)°, and q=0.360. The distributions of constituent cations in the solid solutions are discussed in terms of their ionic radius and site preference effect.  相似文献   

14.
Ba6Ti17O40, Ba4Ti13O30, BaTi4O9, and Ba2Ti9O20 are the only compounds which were found to have a stability range in the subsolidus of the BaTiO3TiO2 system. BaTi2O5 and BaTi5O11, reported in other studies, apparently are not stable. The compound reported as Ba2Ti5O12 appears to have been mistaken for Ba6Ti17O40. X-Ray diffraction powder data are given for this phase which is monoclinic with a = 9.890, b = 17.117, c = 18.933 Å and β=98°42.6′. The phase formulated previously as BaTi3O7 is shown to be Ba4Ti13O30 based on structural and density considerations, phase equilibria, and single crystal and powder X-ray diffraction data. This compound is orthorhombic with a = 17.072, b = 9.862, and c = 14.059 Å, probable space group, Cmca. An idealized structure for this phase is proposed. Ba2Ti9O20 decomposes above 1300°C in the solid state to BaTi4O9 plus rutile. Single crystals were grown using BaF2 as a mineralizer.  相似文献   

15.
方钧  石富城  包蕙质  千坤  姜志全  黄伟新 《催化学报》2013,34(11):2075-2083
利用X射线衍射、N2吸附等温线、X射线光电子能谱、X射线吸收谱、H2-程序升温还原、甲基橙选择化学吸附和等电点测定等方法研究了共沉淀方法制备的一系列CexTi1-xO2复合氧化物的结构. 成功发展了甲基橙选择化学吸附和等电点方法研究CexTi1-xO2复合氧化物的最外层表面结构, 并定义了“等价CeO2表面覆盖度”来描述CexTi1-xO2复合氧化物的最外层表面结构. CexTi1-xO2复合氧化物 (x ≥ 0.7)形成立方萤石相固溶体, Ce0.3Ti0.7O2表现出纯的单斜相, 而其它复合氧化物表现出混合相. CexTi1-xO2复合氧化物最外层表面结构的演变行为不同于其体相结构.Ce0.7Ti0.3O2立方萤石相固溶体最外层表面已经部分形成了单斜相Ce0.3Ti0.7O2, 随Ce含量的降低, 单斜相Ce0.3Ti0.7O2从最外层表面向体相生长. CexTi1-xO2复合氧化物立方萤石相固溶体和单斜相Ce0.3Ti0.7O2分别在相对较低和较高的温度表现出好的还原性能. 上述结果提供了全面和深层次的CexTi1-xO2复合氧化物结构信息.  相似文献   

16.
The quasi ternary phase diagram CaO-MgO-P2O5 at 1000°C for P2O5 ? 33.3 mole-% is determined by heating some 140 compositions prepared from the appropriate ones of 4 starting chemicals (reagent grade CaHPO4, CaCO3, MgO, and MgHPO4 · 3 aq.). Products were investigated with X-ray diffraction and heating was continued until no more changes in phase composition and peak positions in the X-ray diffraction pattern were observed, leading occasionally to heating times of over 1000 hours. There are three major regions of solid solution: for the whitlockite phase, and for the ternary compounds on the pyro- and the ortho-phosphate join. The extent of solid solution of the ternary pyrophosphate compound was determined by the change in peak position in the X-ray diffraction pattern with composition and was found to be 15.9–27.5 mole-% MgO. Two and three phase areas were determined using the change in peak position data for the whitlockite and ternary pyrophosphate compound. The experiments were carried out in air. However additional experiments in a CO2 atmosphere revealed no changes in the X-ray diffraction patterns, apart from those in which apatite was involved. The apatite phase did not incorporate detectable amounts of Mg, not on heating in air nor on heating in a carbondioxide atmosphere.  相似文献   

17.
A systematic study of microstructure and photocatalytic properties of lanthanide doping of nanocrystalline mesoporous titanium dioxide is performed. The anatase-to-rutile (A-R) phase transformation of nanosized TiO2 was significantly inhibited by lanthanide doping and the inhibitory effect was enhanced with the increase of the rare earth radius, i.e., La3+>Gd3+>Yb3+ for different lanthanide dopants. At high calcination temperatures, different texture lanthanide titanium oxides of Ln4Ti9O24 (La3+, Pr3+, Nd3+), Ln2Ti2O7 (Eu3+, Gd3+, Tb3+, Dy3+, Er3+), and Yb2TiO5 were developed, respectively, revealing that the structures of lanthanide titanium oxide developed in Ln/TiO2 depend on the lanthanide radius. Larger radius lanthanides prefer to form higher coordination number lanthanide titanium oxide. In addition, the thermal stability of mesoporous structures of TiO2 was remarkable improved by lanthanide doping. The photocatalytic properties were studied by employing the photodegradation of Rhodamine B (RB) as a probe reaction. The results indicate that the lanthanide doping could bring about significant improvement to the photoreactivity of TiO2, and the improvement was sensitive to the atomic electronic configuration.  相似文献   

18.
Eu3+ ions activated La2Ti2O7 (La2Ti2O7:xEu3+) phosphors have been successfully synthesized by a fractional precipitation method from commercially available La2O3, Eu2O3, HNO3, Ti(SO4)2·9H2O and NH3·H2O as the starting materials. Detailed characterizations of the synthetic products were obtained by fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), differential thermal analysis, thermogravimetry and derivative thermogravimetry (DTA-TG-DTG), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. The results show that the precursor is composed of amorphous particles with quasi-spherical in shape and about 50 nm in size. Moreover, the precursor could be converted into pure La2Ti2O7 phase by calcining at 1000 °C for 2 h in air. The as-synthesized La2Ti2O7 particles are approximate polyhedron in shape and about 100–200 nm in size. PL spectroscopy of La2Ti2O7:xEu3+ phosphors reveals that the strongest emission peak is located at 616 nm under 275 nm ultraviolet (UV) light excitation, which corresponds to the 5D07F2 transition of Eu3+ ions. The quenching concentration of Eu3+ ions is 10.0 mol%, and its corresponding fluorescence lifetime was 1.82 ms according to the linear fitting result. Decay study reveals that the 5D07F2 transition of Eu3+ ions has a single exponential decay behavior.  相似文献   

19.
[(ZrO2)0.92(Y2O3)0.08]0.9(TiO2)0.1 (titania-doped yttria stabilized circonia, 10TiYSZ) samples were prepared by solid state reaction from mixtures of 8 mol% yttria-doped ZrO2 (YSZ) and TiO2 and characterized in terms of structure, microstructure, and electrical properties. [(ZrO2)0.97(Y2O3)0.03]0.9(TiO2)0.1 (titania-doped tetragonal zirconia polycrystalline, 10TiTZP) was also prepared for comparison in some specific studies. Ionic transport properties were measured by impedance spectroscopy in air as a function of temperature. DC techniques including electromotive force (EMF) and Ion Blocking measurements (IB) were carried out in order to determine the electronic contribution to the total conductivity. The addition of titania to YSZ induces the tetragonal zirconia phase formation, thus [(ZrO2)0.92(Y2O3)0.08]0.9(TiO2)0.1 is a composite material and is constituted by two solid solutions, titania-doped yttria-stabilized zirconia (67.7 mole fraction) and titania-doped tetragonal zirconia (32.3 mole fraction). A decrease in bulk ionic conductivity, of one order of magnitude, when TiO2 is added to YSZ is observed in the whole temperature range. Furthermore, in the bulk conductivity vs the reciprocal of the temperature plot, a bending (from 550°C to higher temperatures) toward higher activation energies was detected. The bending could indicate the existence mainly of Ti4+-Vö associated pairs with an association energy of 0.43±0.02 eV. It could mean that Ti-O bonds become stronger and shorter and could produce the formation of microdomains of a ZrTiO4-like structure. The addition of titanium is effective in increasing the electronic conductivity under reducing conditions. Conductivity as a function of Po2 and IB results cannot be related to the formation of small polarons during the reduction process. Furthermore, according to the calculations based on the small polaron theory, inconsistent values for the radius of a small polaron (rp) are obtained in both 10TiYSZ and 10TiTZP. However, large polarons can explain the transport properties in these materials under reducing conditions in agreement with the experimental data.  相似文献   

20.
采用静电纺丝技术制备的TiO2纤维作为模板和反应物,通过原位水热合成了具有异质结构的Bi2Ti2O7/TiO2复合纤维。利用X射线衍射(XRD)、扫描电镜(SEM)、能量散射光谱(EDS)、高分辨透射电镜(HRTEM)和紫外可见吸收光谱(UV-Vis)等分析测试手段对样品的结构和形貌进行表征。以罗丹明B为模拟有机污染物进行光催化降解实验。结果表明:花状Bi2Ti2O7纳米结构均匀地生长在TiO2纤维上,制备了Bi2Ti2O7与TiO2相复合的光催化材料,其光谱响应范围拓宽至可见光区,与纯TiO2纤维相比可见光催化活性显著提高,且易于分离、回收和循环使用。初步探讨了Bi2Ti2O7/TiO2异质结的生长机制和光催化活性提高机理。  相似文献   

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