PCVD法制备ZrO~2和YSZ薄膜

以金属β-二酮类有机螯合物Zr(DPM)~4和Y(DPM)~3为挥发性源物质, 采用微波等离子体化学气相淀积法于较低的温度下(420～560℃)成功地在多孔α-Al~2O~3陶瓷,非晶玻璃等衬底上制备出致密的ZrO~2和YSZ薄膜材料.XRD分析结果表明,纯ZrO~2薄膜中除了单斜相外还存在着亚稳态的四方相.当掺入的Y~2O~3 摩尔百分含量大于或等于7%时,ZrO~2完全被稳定成立方相.SEM观察表明, 在等离子体内的不同区域中生成的薄膜形貌有所不同.XPS检测了YSZ薄膜中Zr3d~5~/~2和Zr3d~3~/~2 的电子结合能,发现较ZrO~2的标准值低0.7eV.由TEM观察和由XRD衍射峰半宽度计算, 所制备的ZrO~2和YSZ薄膜中微晶粒径在10nm左右     

Order and disorder effects in nano-ZrO(2) investigated by micro-Raman and spectrally and temporarily resolved photoluminescence

Pure and europium (Eu(3+)) doped ZrO(2) synthesized by an oil-in-water microemulsion reaction method were investigated by in situ and ex situ X-ray diffraction (XRD), ex situ Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), steady state and time-resolved photoluminescence (PL) spectroscopies. Based on the Raman spectra excited at three different wavelengths i.e. 488, 514 and 633 nm and measured in the spectral range of 150-4000 cm(-1) the correlation between the phonon spectra of ZrO(2) and luminescence of europium is clearly evidenced. The PL investigations span a variety of steady-state and time resolved measurements recorded either after direct excitation of the Eu(3+) f-f transitions or indirect excitation into UV charge-transfer bands. After annealing at 500 °C, the overall Eu(3+) emission is dominated by Eu(3+) located in tetragonal symmetry lattice sites with a crystal-field splitting of the (5)D(0)-(7)F(1) emission of 20 cm(-1). Annealing of ZrO(2) at 1000 °C leads to a superposition of Eu(3+) emissions from tetragonal and monoclinic lattice sites with monoclinic crystal-field splitting of 200 cm(-1) for the (5)D(0)-(7)F(1) transition. At all temperatures, a non-negligible amorphous/disordered content is also measured and determined to be of monoclinic nature. It was found that the evolutions with calcination temperature of the average PL lifetimes corresponding to europium emission in the tetragonal and monoclinic sites and the monoclinic phase content of the Eu(3+) doped ZrO(2) samples follow a similar trend. By use of specific excitation conditions, the distribution of europium on the amorphous/disordered surface or ordered/crystalline sites can be identified and related to the phase content of zirconia. The role of zirconia host as a sensitizer for the europium PL is also discussed in both tetragonal and monoclinic phases.     

Solvothermal and surfactant-free synthesis of crystalline Nb(2)O(5), Ta(2)O(5), HfO(2), and Co-doped HfO(2) nanoparticles

A simple route to niobium, hafnium and tantalum oxide nanocrystals using a nonaqueous sol-gel route based on the solvothermal reaction of the corresponding metal chlorides with benzyl alcohol is presented. This approach can easily be extended to the preparation of high quality Co-doped HfO(2) nanoparticles of uniform size and shape and with a homogenous distribution of the magnetic ions. The structural characterization of all these nanomaterials as well as the magnetic properties of pure and doped hafnia, with special attention to the doping efficiency, are discussed. The obtained Co-doped hafnia exhibits paramagnetic properties with very weak antiferromagnetic interactions between Co ions moments.     

Hafnia sol-gel films synthesized from HfCl4: Changes of structure and properties with the firing temperature

Thin sol-gel hafnia films have been synthesised from HfCl₄, the synthesis has revealed to be a simple route to fabrication of hafnia films with high transparency in the UV-visible range. The films have been fired at different temperatures in air up to 1000°C and have been characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Infrared absorption spectra of hafnia films have allowed to follow the formation of monoclinic crystalline phases together with XRD. Formation of monoclinic hafnia crystallites has been observed upon calcination at temperatures higher than 600°C, as shown by infrared spectroscopy and XRD. The optical transmission and the refractive index as a function of the temperature of firing have been characterized by UV-Visible spectroscopy and spectroscopic ellipsometry. The hafnia films, after firing at 600°C, had a refractive index of 1.92 with a thickness of around 70 nm.     

HfO2:X (X = Eu(3+), Ce(3+), Y(3+)) sol gel powders for ultradense scintillating materials

Hafnium dioxide (HfO 2) presents a high crystalline density which makes it attractive for host lattice activated by rare earths for applications as scintillating materials. HfO 2 powders doped with Eu (3+) or Ce (3+) luminescent ions are prepared by sol gel process. The annealing temperature and the concentration of doping ions are optimized to provide the powder presenting the best scintillation yield. The powders are crystallized in monoclinic phase whatever annealing temperature above 800 degrees C. The emission spectra are characterized by a white broadband between 400 and 600 nm. After optimization, the most efficient composition, namely HfO 2:2.5% Eu 1% Y (molar percent) exhibits a scintillation yield about 31,000 photons/MeV, which is about 3.8 times that of the standard Bi 3Ge 5O 12 (BGO) commercial powder.     

Hydrothermal/microwave and hydrothermal/ultrasonic synthesis of nanocrystalline titania,zirconia, and hafnia

We compare the physical-chemical properties (X-ray diffraction (XRD), powder X-ray diffraction, TGA, TEM, and BET) of titania, zirconia, and hafnia nanopowders (d = 10–15 nm) synthesized from amorphous titanyl hydroxide TiO₂ · nH₂O, zirconyl hydroxide ZrO(OH)₂ · nH₂O, and hafnyl hydroxide HfO(OH)₂ · nH₂O using hydrothermal (HT), hydrothermal/microwave (HT-MW), and hydrothermal/ultrasonic (HT-US) methods at 150, 180, and 250°C with treatment lasting 0.5–24 h. Titania, zirconia, and hafnia crystallization from amorphous hydroxides is substantially enhanced, and the percentage of the thermally stable zirconia phase (m-ZrO₂) in the HT-MW and HT-US processes increases compared to conventional HT synthesis. The observed similar effects have completely different causes. A common factor in both cases is likely the uniformity of heating of treated suspensions. Local overheating in the reaction mixture, which appears during both ultrasonication and microwave treatment, can also play a role in accelerating the hydrothermal processes.     

Photoluminescence and Raman studies of Sm3+ and Nd3+ ions in zirconia matrices: example of energy transfer and host-guest interactions

Photoluminescence and Raman studies on Sm(3+)- and Nd(3+)-doped zirconia are reported. The Raman studies indicate that the monoclinic (m) phase dominates up to a 10 at.% lanthanide level, while stabilization of the cubic phase is attained at approximately 20 and approximately 25 at.% of Sm(3+) and Nd(3+), respectively. Both systems are strongly luminescent under photo-excitation. The emission spectrum at 77 K of the ZrO(2):Sm(3+) system consists of a broad band at 505 nm, that corresponds to the zirconia matrix. At room temperature the band maximum blue-shifts to 490 nm. Sharper bands corresponding to f-f transitions within the Sm(3+)ion are also exhibited in the longer wavelength region of the spectrum. Exclusive excitation of the zirconia matrix provides sensitized emission from the acceptor Sm(3+) ion. The excitation profile is dominated by a broad band at 325 nm when monitored either at the zirconia or at one of the Sm(3+) emissions. A spectral overlap between the 6H(5/2)-->(4)G(7/2) absorption of the Sm(3+) ion with the zirconia emission leads to an efficient energy transfer process in the systems. Multiple facets of the spectral behavior of the Sm(3+) or Nd(3+) in the zirconia matrices, as well as the effects of compositions on the emission and Raman properties of the materials, and the role of defect centers in photoluminescence and the energy transfer processes are discussed.     

Structure of Electrochemically Lithiated Li_(0.33)MnO_2

Li0.33MnO2 cathode material was synthesized by solid state reaction which showed a monoclinic structure.In situ synchrotron diffraction showed a reversible structural transition of Li0.33MnO2 during Li+ insertion/extraction.However,it is difficult to determine the crystal structure of lithiated Li0.33+xMnO2 based on their poorly resolved diffraction patterns.This difficulty was successfully resolved by X-ray absorption spectroscopy(XAS) and Raman scattering which are sensitive to the short-range ordering of...     

Applied magnetic field rejects the coating of ferromagnetic carbon from the surface of ferromagnetic cobalt: RAPET of CoZr2(acac)2(OiPr)8

We present the results of the RAPET (reaction under autogenic pressure at elevated temperatures) dissociation of CoZr(2)(acac)(2)(O(i)Pr)(8) at 700 degrees C in a closed Swagelok cell under an applied magnetic field of 10 T. It produces a mixture of carbon-coated and noncoated metastable ZrO(2) nanoparticles, bare metallic Co nanoparticles, and bare carbon. The same reaction in the absence of a magnetic field produces spherical Co and ZrO(2) particles in sizes ranging from 11 to 16 nm and exhibiting, at room temperature, metastable phases: fcc for cobalt and a tetragonal phase for zirconia. The metastable phases of Co and ZrO(2) are manifested because of a carbon shell of approximately 4 nm thickness anchored to their surfaces. The effect of an applied magnetic field to synthesize morphologically different, but structurally the same, products is the key topic of the present paper.     

Surface functionalization of ZrO2 nanocrystallites for the integration into acrylate nanocomposite films

Surface functionalized zirconia nanoparticles were prepared by covalent grafting of a methacrylate functionalized silane (methacryloxypropyltrimethoxysilane, MPTS) onto the surface of the zirconia nanoparticles (tetragonal and mixed monoclinic/tetragonal phase) obtained by hydrothermal treatment of zirconyl chloride octahydrate. The particles are 70 nm aggregates of nanometric primary grains (4-12 nm) with inter particle porosity. BET measurements show that the specific surface area of the particles after activation at 100 degrees C is between 85 and 204 m2/g depending on the mineralizer used (Sr2+, Ca2+, Mg2+). IR-measurements show that the surface of the particles can be covered with functional groups bound through a variable number of ZrOSi bonds to render them organocompatible. The surface modified particles were dispersed in monomer solution (butanediol monoacrylate, BDMA) and polymerized to form films by adding a cross linking agent (trimethylolpropane triacrylate, Laromer TMPTA) and an UV initiator (2,4,6-trimethylbenzoyldiphenylphosphine oxide, Lucirin TPO). The received films were characterized with thermogravimetry and UV-vis spectroscopy.     

Mesostructure,fractal properties and thermal decomposition of hydrous zirconia and hafnia

By use of small angle and ultra small angle neutron scattering techniques it was established that amorphous xerogels of hydrous zirconia and hafnia possess fractal properties in a wide range of scales, and the fractal dimension of these materials can be intentionally modified by changing their precipitation pH. It was found that the changes in fractal dimension and specific surface area of hydrous zirconia and hafnia xerogels are governed by the changes in the adsorption of anions onto their surface. It was demonstrated that particle size and specific surface area of ZrO₂ and HfO₂ nanopowders prepared by thermal decomposition of hydrous zirconia and hafnia xerogels depends strongly on the mesostructure and synthesis conditions of these xerogels.     

氧化铝对Pt-SO4^2-／ZrO2-Al2O3固体酸催化剂结构与酸性的影响

通过混捏法制备了Pt-SO4^2-／ZrO2-Al2O3固体酸催化剂，考察了该催化剂在正构烷烃低温异构化反应中的催化稳定性．采用X射线衍射、差热分析、X射线光电子能谱、核磁共振、N2吸附-脱附和微量热等表征技术，对氧化铝的作用机理进行了研究．结果表明，氧化铝起到结构助催化剂作用，对四方相氧化锆具有稳定作用，并延迟了氧化锆的晶化，抑制了氧化锆的烧结，从而增大了催化剂的比表面积和孔容．XPS结果表明，Zr3d峰向低结合能方向移动，Al2p峰向高结合能方向移动，说明Al^3＋的电子向Zr^4＋偏移．微量热结果表明氧化铝的引入提高了催化剂的酸量和酸强度．^27Al固体核磁共振结果表明，Pt-SO4^2-／ZrO2-Al2O3中的六配位铝的结构发生了变化．氧化铝的引入还可能有助于氧化锆晶格缺陷的形成，焙烧过程中Al^3＋迁移进入氧化锆晶格并同晶取代Zr^4＋形成氧缺陷位，这些氧缺陷位在S=O键诱导下显示强酸性．     

Luminescence of monolayer thin films of the fully conjugated rigid‐rod polymer poly(p‐phenylenebenzobisthiazole)

Poly(p‐phenylenebenzobisthiazole) (PBT) is a heterocyclic, aromatic rigid‐rod polymer with a fully conjugated backbone and excellent dimensional, thermo‐oxidative, and solvent stabilities. A PBT polymer with an intrinsic viscosity of 18.0 dL/g was dissolved in methanesulfonic acid or Lewis acid. The PBT solution was spin‐coated and doctor‐bladed for freestanding films or onto an indium tin oxide (ITO) substrate. The acid was removed via coagulation. Scanning electron microscopy determined that the resultant film thicknesses were about 340 and 60 nm for PBT freestanding films and films on the ITO substrate, respectively. X‐ray scattering demonstrated that the freestanding films were in‐plane isotropic without long‐range order. The freestanding films were excited with a He‐Cd laser at 325 nm for photoluminescence (PL) response. PL spectra showed a distinct intensity maximum at 580 nm, regardless of the film‐forming conditions. After the films cooled to 67 K, the PL maximum shifted to 566 nm with enhanced intensity. Aluminum was evaporated onto the monolayer PBT thin film on the ITO substrate as an electron injector for electroluminescence (EL) response. Diodic electric behavior was observed for all monolayer PBT EL devices for the first time. A threshold voltage as low as 4 V was achieved for the monolayer EL devices. In addition, PBT EL spectra were tunable, with a maximum intensity at 570 nm at a bias voltage of 4.5 V changing to 496 nm at 7.5 V (i.e., a blueshift) with greatly increased intensity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1760–1767, 2002     

Oxygen-containing gas-phase diatomic trications and tetracations: ReO(z+), NbO(z+) and HfO(z+) (z=3, 4)

Three oxygen-containing gas-phase diatomic trications ReO(3+), NbO(3+) and HfO(3+) as well as the diatomic tetracation NbO(4+) have been observed by mass spectrometry at non-integer m/z values. These unusual triply charged molecular ion species, together with the corresponding diatomic dications ReO(2+), NbO(2+) and HfO(2+), were produced by energetic, high-current oxygen ((16)O(-)) ion beam sputtering of rhenium, niobium and hafnium metal samples, respectively, whose surfaces were dynamically oxidized by oxygen primary ion incorporation. In addition, NbO(z+) (z≤ 4) were generated by intense femtosecond laser excitation and photofragmentation (Coulomb explosion) of Nb(x)O(y) clusters and were detected through Time-of-Flight Mass Spectrometry (TOF). Our experimental results confirm previous reports on the detection of NbO(4+), NbO(3+), NbO(2+), HfO(3+) and HfO(2+) with Atom Probe mass spectrometry, whereas ReO(3+) and ReO(2+) apparently had not been observed before. In addition, these multiply charged molecular ions have been studied theoretically for the first time. Ab initio calculations of their electronic structures show that the diatomic trications ReO(3+), NbO(3+) and HfO(3+) are long-lived metastable gas-phase species, with bond lengths of 1.61 ?, 1.62 ? and 1.86 ?, respectively. They present large potential barriers with respect to dissociation of more than 2.7 eV. The corresponding diatomic dications are thermochemically stable molecules with very large dissociation energies (>3.5 eV). Our calculations predict the diatomic tetracation ReO(4+) to be a metastable ion species in the gas phase. We compute a potential barrier toward fragmentation of 0.6 eV; its formation requires a quadruple adiabatic ionization energy of 85.7 eV. Even though our calculations show that NbO(4+) is a weakly bound (dissociation barrier ～0.1 eV) metastable molecule, it is here identified via linear time-of-flight mass spectrometry.     

Raman Spectrum of Er-Y-codoped ZrO2 and Fluorescence Properties of Er3+

Er-Y-codoped ZrO2 mixed oxides with monoclinic, tetragonal and cubic structures were prepared by a sol-gel method. The crystal structure of ZrO2 matrix and the effect of the ZrO2 phases on the fluorescence properties of Er3+ were studied using Raman spectroscopy. The results indicated that the fluorescence properties of Er3+ depend on its local ZrO2 crystal structures. As ZrO2 matrix transferred from monoclinic to tetragonal and cubic phase, the Raman and fluorescence bands of Er3+ decreased in intensities and tended to form a single peak. With 632.8 nm excitation, the bands between 640 and 680 nm were attributed to the fluorescence of Er3+ in the ZrO2 environment. However, only the fluorescence was observed and no Raman spectra were seen under 514.5 nm excitation, while only Raman spectra were observed under 325 nm excitation. UV Raman spectroscopy was found to be more sensitive in the surface region while the information provided by XRD mainly came from the bulk. The phase with lower symmetry forms more easily on the surface than in the bulk.     

X-ray, Raman and FTIRS studies of the microstructural evolution of zirconia particles caused by the thermal treatment

Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO₃)₂ solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 °C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO₂. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) already after a mild calcination at 500 °C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600-650 °C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM.     

Synthesis and crystal structure of barium thioborate Ba7(BS3)4S

The thioborate phase Ba7(BS3)4S was synthesized from solid state reaction and its crystal structure determined by single crystal X-ray diffraction analysis. It crystallizes in the monoclinic space group C2/c (No. 15) with a = 10.1750(15) A, b = 23.970(4) A, c = 10.1692(15) A, beta = 90.095(2) degrees, and Z = 4. The structure consists of isolated trigonal planar (BS3)3- anions, and isolated S2- anions and Ba2+ cations. The additional sulfur anions have five-fold barium coordination, while the barium cations are coordinated by eight or nine sulfur atoms. Powder X-ray diffraction patterns from a bulk sample are compared to the calculated diffraction pattern from the single crystal structural analysis, and there is excellent agreement in general. The vibrational modes of the isolated (BS3)3- units were measured from Raman scattering and IR absorption spectra, and the frequencies agree very well with those found for similar orthothioborate phases.     

Gasochromic Behavior of Sol-Gel Derived Pd Doped Peroxopolytungstic Acid (W-PTA) Nano-Composite Films

The behavior of sol-gel prepared thin films exhibiting a gasochromic effect; i.e., a reversibly change in colour from transparent when in air to blue when in H2, has been studied. The films were prepared from a Pd (PdCl2) doped peroxopolytungstic acid sol using a dip-coating technique. Transmission electron microscopy together with selected area electron diffractrometry revealed that the films consist of monoclinic and hexagonal nanocrystalline grains (2–5 nm) embedded in an amorphous phase. This amorphous hydrated phase was established using Infrared (IR) and Raman spectroscopy. Characteristic vibrations observed in the in-situ IR spectra of the coloured and bleached states revealed the presence and the importance of terminal W=O and W—OH2 groups in the colouring of the films. Colouring/bleaching changes of Pd doped W-PTA films observed using in-situ UV-Vis spectroscopy are described in terms of Pd concentration, and the number of reducing/oxidising cycles. The rate of colouring/bleaching is greater for films containing a higher concentration of Pd but the change in the optical density does not increase, i.e., shows saturation.     

A low-temperature, soft chemistry method for the synthesis of zirconia nanoparticles in thermally evaporated fatty amine thin films

We demonstrate the synthesis of zirconia nanoparticles in a lipid matrix by a simple, low temperature beaker-based process. This is accomplished by electrostatic entrapment of ZrF6(2-) ions within thermally evaporated octadecylamine (ODA) thin films followed by the low-temperature in situ hydrolysis of the entrapped metal ion complexes. The zirconia particles thus formed were of the monoclinic phase and were fairly monodisperse with particles of average size 40 nm. The zirconia crystallites appeared to exhibit preferred orientation indicating epitaxial growth of the crystals within the lipid matrix. The formation of zirconia nanoparticles in the lipid matrix was investigated using quartz crystal microgravimetry (QCM), optical absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques.     

A comparative study of the surface structure, acidity, and catalytic performance of tungstated zirconia prepared from crystalline zirconia or amorphous zirconium oxyhydroxide

Tungstated zirconias prepared from W deposition on zirconium oxyhydroxide are reportedly active for alkane isomerization, whereas solids synthesized by impregnation of zirconia are inactive. The origin of the differences between the two preparations is not fully understood. The present paper examines the influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performance of WO(x)()/ ZrO(2) catalysts. Two series of catalysts containing W surface densities up to 5.2 at. W/nm(2) were prepared by pore volume impregnation of two different supports: zirconium oxyhydroxide and predominantly tetragonal zirconia (65% tetragonal, 35% monoclinic). The texture and structure of the catalysts were investigated by BET measurements, X-ray diffraction, Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of Zr oxyhydroxide, Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. The development of the acidity was monitored by lutidine adsorption and desorption at 523 K, followed by infrared spectroscopy. The results indicated the presence of a threshold of W surface density at 1.3 at. W/ nm(2) for the detection of these acid sites, followed by a progressive increase in their abundance with increasing W surface density. The development of Br?nsted acidity correlated with the evolution of the infrared bands attributed to "extensively" polymerized W species. A direct relationship was observed between the abundance of Br?nsted acid sites and the catalytic activity for 2-propanol dehydration. For n-hexane isomerization, compared to 2-propanol dehydration, a higher threshold of W surface densities (3.4 at. W/ nm(2)) for the development of activity was observed. The difference was attributed to stronger Br?nsted acid sites required for n-hexane isomerization. The catalysts prepared by impregnation of zirconia exhibited comparable behavior. For a given W surface density, the crystalline composition of the support (tetragonal/monoclinic zirconia), the W surface structure, abundance of Br?nsted acid sites, and catalytic performance were similar. Thus, in an apparent variance with some of the results reported in the literature with respect to the influence of preparation methods, no significant effect of the initial form of the support (Zr oxyhydroxide versus predominantly tetragonal zirconia) was evidenced.