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1.
采用高温固相法合成了铈掺杂的K2La2Ti3O10催化剂, 利用X射线衍射(XRD)、紫外-可见漫反射(UV-vis DRS)、透射电镜(TEM)和X射线光电子能谱(XPS)对催化剂进行了表征. 考察了催化剂的可见光催化分解甲醇水溶液制氢的活性, 并对可见光催化机理进行了分析. 研究表明, 铈的掺杂没有改变K2La2Ti3O10的微晶结构, 并使催化剂粒径有所减小. 紫外可见漫反射分析表明禁带宽度为2.3 eV左右, 对可见光具有较高吸收. XPS表明La和Ti为+3和+4价, 而Ce则是+3和+4的混合价态. 担载2 wt% Pt后, 在可见光下光催化活性大大提高, 当铈的掺杂量为0.5 mol%(即Ce取代La的摩尔百分量)时, 光催化活性达到最大, 产氢速率为0.05 mmol/h; 光照5 h后产氢量为0.22 mmol, 而纯K2La2Ti3O10的产氢量只有0.037 mmol. 相似文献
2.
The ferroelectric ceramics of Bi4Ti3O12, SrBi4Ti4O15, and lanthanum-doped Bi4Ti3O12-SrBi4Ti4O15 were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi4Ti3O12-SrBi4Ti4O15. The structure of the Bi2O2 layers and TiO6 octahedra of the intergrowth was found to be different from those of Bi4Ti3O12 and SrBi4Ti4O15. La3+ ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi2O2 layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi4Ti3O12-SrBi4Ti4O15. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi2O2 slabs. 相似文献
3.
La_2Ti_6O_(15)-CeTi_(21)O_(38)-PbTiO_3 ceramics formed in gaseous penetration of La-Ce into PbTiO_3 and their electric properties 总被引:2,自引:0,他引:2
PbTiO3 ceramics, which are typical ferroelectric materials, are useful in various applied fields. For example, it has a very good candidacy for piezoelectric materials for high temperature and high sensibility. In recent years, the studies on doped PbTiO3 ceramics have received consid-erable attention[1—3]. The modified PbTiO3 ceramics doped with Ca2+, Sm3+, Y3+, Ce4+ etc. have some better properties: their Curies temperature decreases, their tetragonal distortion degree de-grades and th… 相似文献
4.
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
5.
Karl R. Whittle Gregory R. Lumpkin Robert D. Aughterson Nestor J. Zaluzec 《Journal of solid state chemistry》2010,183(10):2416-2420
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
6.
Hyunsoo Park 《Journal of solid state chemistry》2004,177(1):159-164
The compound previously reported as Ba2Ti2B2O9 has been reformulated as Ba3Ti3B2O12, or Ba3Ti3O6(BO3)2, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO3:BaTiB2O6 (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F2)=0.039 for 504 unique reflections. Ba3Ti3O6(BO3)2 is isostructural with K3Ta3O6(BO3)2. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba3Ti3O6(BO3)2 is equal to 95% of that of LiNbO3. 相似文献
7.
Cui Wenquan Liu Li Feng Liangrong Xu Chenghua Li Zijian Lü Shaojie Qiu Fali 《中国科学B辑(英文版)》2006,49(2):162-168
A layered perovskite-type oxide K2La2Ti3O10 was prepared with high-temperature solid-state reaction, and characterized with X-ray diffraction (XRD) and ultraviolet-visible
diffuse reflectance spectroscopy (UV-Vis DRS). Platinum was loaded onto K2La2Ti3O10 as a co-catalyst with different methods. The dispersion of platinum on K2La2Ti3O10 was determined with HOT method. The photocatalytic activity of Pt/K2La2Ti3O10 was studied. This catalyst showed much higher activity in hydrogen evolution reaction than Ni/K2La2Ti3O10. The effects of different amounts of loaded platinum and several preparation methods were evaluated. The best achieved hydrogen
evolution rate was 233.88 μmol·h−1 by Pt(2%)/K2La2Ti3O10. A possible band structure and mechanism were discussed based on the results. 相似文献
8.
采用优化的高温固相方法制备了稀土离子Eu3+和Tb3+掺杂的La7O6(BO3)(PO4)2系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La7O6(BO3)(PO4)2:Eu3+材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D0→7F2特征能级跃迁,Eu3+的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La7O6(BO3)(PO4)2:Tb3+材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb3+的5D4→7F5能级跃迁,Tb3+离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu3+和Tb3+掺杂的La7O6(BO3)(PO4)2荧光材料均具有良好的热稳定性。 相似文献
9.
Garnet-structure related metal oxides with the nominal chemical composition of Li5La3Nb2O12, In-substituted Li5.5La3Nb1.75In0.25O12 and K-substituted Li5.5La2.75K0.25Nb2O12 were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li5La3Nb2O12. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In3+(rCN6: 0.79 Å) for smaller Nb5+ (rCN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K+ for La3+ and In3+ for Nb5+ in Li5La3Nb2O12 exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li5.5La3Nb1.75In0.25O12 exhibits the highest bulk lithium ion conductivity of 1.8×10−4 S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10−10-10−7 cm2/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li5La3Nb2O12 was found to be unsuccessful under the investigated conditions. 相似文献
10.
Magnetic diphase nanostructures of ZnFe2O4/γ-Fe2O3 were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe2O4/γ-Fe2O3 was formed, in which the presence of ZnFe2O4 enhanced the thermal stability of γ-Fe2O3. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe2O3. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe2O3 content. 相似文献
11.
The phase system Al2O3-TiO2 was investigated in the compositional range from 48:52 to 62:38 mol% Al2O3:TiO2. The samples were prepared by melting the binary oxides in an arc-imaging furnace and the obtained samples were examined by powder X-ray diffraction. The recorded powder patterns could be interpreted in terms of intergrowth structures consisting of two basic building blocks, which were deduced from the known crystal structures of β-Al2TiO5 and Al6Ti2O13. The structure of a new ordered compound with the formula Al16Ti5O34 is proposed. The thermal stability was estimated from DTA and tempering experiments and showed that all prepared samples decompose at temperatures around 800 °C into the binary oxides corundum and titania. 相似文献
12.
采用优化的高温固相方法制备了稀土离子Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La_7O_6(BO_3)(PO_4)_2∶Eu~(3+)材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D0→7F2特征能级跃迁,Eu~(3+)的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La_7O_6(BO_3)(PO_4)_2∶Tb~(3+)材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb~(3+)的5D4→7F5能级跃迁,Tb~(3+)离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2荧光材料均具有良好的热稳定性。 相似文献
13.
通过调节溶液的pH值,在水热条件下合成出长径比为2-45的La(OH)3纳米棒. 对水热合成过程中间体的结构演变分析,发现高碱度有利于小尺寸晶核的形成,La(OH)3晶体结构的各向异性导致这些晶种沿着C轴方向生长,进而形成纳米棒结构. 将La(OH)3纳米棒前驱体于773 K焙烧可以得到长径比为2-20的La2O2CO3纳米棒. 随着长径比的增加,La2O2CO3纳米棒暴露的(110)晶面逐渐增加,La3+-O2-碱性位的数目也从0.08增加到0.24 mmol/g. 因此,在Claisen-Schmidt缩合反应中,La2O2CO3纳米棒催化剂上的反应速率随着长径比的增加而逐渐增大. 相似文献
14.
用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。 相似文献
15.
P. Berastegui S. HullF.J. Garc? Garc? J. Grins 《Journal of solid state chemistry》2002,168(1):294-305
The structures of the oxyorthogermanate La2(GeO4)O and the apatite-structured La9.33(GeO4)6O2 have been refined from powder neutron diffraction data. La2(GeO4)O crystallizes in a monoclinic unit cell (P21/c) and is cation stoichiometric in contrast to previous reports. La9.33(GeO4)6O2 crystallizes in a hexagonal unit cell (P63/m) and the powder diffraction data show anisotropic peak broadening that is observed in electron diffraction patterns as incommensurate diffuse spots at hkq reciprocal planes (with q=1.6-1.7) and can be attributed to a correlated disorder in the “apatite channels”. This compound was doped up to a nominal composition close to M2La8(GeO4)6O2 with M=Ca, Sr, Ba. The dopant ions preferentially occupy the 4f sites as the number of La vacancies decreases. The measured ionic conductivity of La9.33(GeO4)6O2 is about 3 orders of magnitude larger than for La2(GeO4)O at high temperatures and decreases with increasing dopant content from the highest value of about 0.16 S cm−1 at 1160 K. 相似文献
16.
采用固相法合成了尖晶石型LiMn2O4,并通过溶胶-凝胶法制备了不同物质的量的百分比含量Li4Ti5O12包覆的正极材料。X-射线衍射和扫描电镜结果表明,Li4Ti5O12微粒包覆在LiMn2O4的表面没有产生晶体结构的变化。实验电池在室温下,以1C,2C和5C倍率作充放电循环测试;结果表明,与未包覆的LiMn2O4相比,表面包覆Li4Ti5O12微粒的正极材料在高倍率下具有更好的循环稳定性。 相似文献
17.
Shinji Kosaka Takumi Fujiwara Takayuki Komatsu 《Journal of solid state chemistry》2005,178(6):2067-2076
The ternary BaO-TiO2-B2O3 glasses containing a large amount of TiO2 (20-40 mol%) are prepared, and their optical basicities (Λ), the formation, structural features and second-order optical nonlinearities of BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO2 contents of 30-40 mol% show large optical basicities of Λ=0.81-0.87, suggesting the high polarizabity of TiOn polyhedra (n=4-6) in the glasses. BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO3)2 crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba3Ti3O6(BO3)2 phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses were found to be 0.8 times as large as α-quartz powders, i.e., I2ω(sample)/I2ω(α-quartz)=0.8, for the sample with BaTi(BO3)2 crystals and to be I2ω(sample)/I2ω(α-quartz)=68 for the sample with Ba3Ti3O6(BO3)2 crystals. The Raman scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed. 相似文献
18.
La2Mo2O9 ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La2Mo2O9 from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries. 相似文献
19.
采用水热法合成球形钛酸铋复合氧化物光催化剂,利用SEM、XRD和UV-Vis DRS等表征手段对复合氧化物的晶体结构、微观形貌和光学性能进行了分析,结果表明,制备的钛酸铋复合氧化物为10 nm的球形颗粒,具有良好的晶型结构,禁带宽度为2.7 nm,有较好的可见光吸收能力。以亚甲基蓝、甲基橙及酸性品红为目标污染物,研究了复合氧化物在可见光下的光催化降解有机污染物的性能,并对光催化降解机理进行了探讨。结果表明,在可见光照射下,该复合氧化物对酸性品红降解效果明显优于亚甲基蓝和甲基橙,光照150 min下,降解率可达91%。 相似文献
20.
采用水热法合成球形钛酸铋复合氧化物光催化剂,利用SEM、XRD和UV-Vis DRS等表征手段对复合氧化物的晶体结构、微观形貌和光学性能进行了分析,结果表明,制备的钛酸铋复合氧化物为10 nm的球形颗粒,具有良好的晶型结构,禁带宽度为2.7 nm,有较好的可见光吸收能力。以亚甲基蓝、甲基橙及酸性品红为目标污染物,研究了复合氧化物在可见光下的光催化降解有机污染物的性能,并对光催化降解机理进行了探讨。结果表明,在可见光照射下,该复合氧化物对酸性品红降解效果明显优于亚甲基蓝和甲基橙,光照150 min下,降解率可达91%。 相似文献