Ti：LiAlO2新型晶体的结构分析

通过研究提拉法生长的掺杂Ti浓度为0.2at%的LiAlO2晶体吸收光谱,荧光光谱和红外光谱,来分析此新型晶体的结构.分析发现光谱中仅出现了四价Ti离子的196nm的特征吸收峰,用235nm光激发得到384nm的特征发射峰;针对吸收光谱中660-820nm出现的四个弱小吸收峰提出了一个色心模型,从而解释了空气和富Li气氛处理后吸收峰消失的现象;对比纯LiAlO2晶体的红外光谱发现,Ti的掺入仅影响了[AlO4]键强,而[LiO4]及相关键强几乎不变;结合ICP测试估算出直径50mm,厚1mm的Ti：LiA

Spectra analysis of a novel Ti-doped LiAlO2 single crystal

LiAlO2 single crystals doped with Ti at concentration 0.2 at.% are grown by the Czochralskl technique with dimensions Phi 42 x 55 mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the V-Li and V-O absorptions, respectively. The peaks at 716nm and 798nm may stem from the V-Li(+) and F+ absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals.

提拉法Ti:LiAlO_2晶体的生长、缺陷及N_2退火研究

本文采用提拉法成功地生长了钛掺杂浓度为0.1%原子分数的LiAlO2单晶体,借助光学显微镜,结合化学腐蚀法,对Ti:LiAlO2晶体(100)面空气退火前后的缺陷特征进行了研究,用AFM观测了(100)面晶片在不同温度下流动N2气氛退火过的表面形貌。结果表明:Ti:LiAlO2晶体(100)面的位错腐蚀坑是底面为平行四边形的锥形坑,位错密度约为5.0×104cm-2,900℃空气退火后晶片表面的位错腐蚀坑变大;N2退火能显著影响晶片的表面形貌,当退火温度为900℃时,晶片的均方根粗糙度(RMS)达到最低值

新型掺杂LiAlO2晶体衬底研究

本文系统研究了LiAlO2晶体及掺钛0．2％原子分数LiAlO2晶体的水解性能，用原子力显微镜对（100）晶片在不同水解时间下的表面形貌进行了观察，对比发现这两种晶体的（100）面均具有极性和易水解性。同时观察到掺钛LiAlO2晶体的抗水解性比纯LiAlO2晶体更好，因为掺钛LiAlO2晶体有更多的Li空位，水解的活性得到降低。

Raman spectroscopic study of the antimonate mineral lewisite (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7

The mineral lewisite, (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7 an antimony bearing mineral has been studied by Raman spectroscopy. A comparison is made with the Raman spectra of other minerals including bindheimite, stibiconite and roméite. The mineral lewisite is characterised by an intense sharp band at 517 cm-1 with a shoulder at 507 cm-1 assigned to SbO stretching modes. Raman bands of medium intensity for lewisite are observed at 300, 356 and 400 cm-1. These bands are attributed to OSbO bending vibrations. Raman bands in the OH stretching region are observed at 3200, 3328, 3471 cm-1 with a distinct shoulder at 3542 cm-1. The latter is assigned to the stretching vibration of OH units. The first three bands are attributed to water stretching vibrations. The observation of bands in the 3200 to 3500 cm-1 region suggests that water is involved in the lewisite structure. If this is the case then the formula may be better written as Ca, Fe2+, Na)2(Sb, Ti)2(O,OH)7 •xH2O.

Raman spectroscopic study of the arsenite minerals leiteite ZnAs2O4 , reinerite Zn3(AsO3)2 and cafarsite Ca5(Ti,Fe,Mn)7(AsO3)12.4H2O

The selected arsenite minerals leiteite, reinerite and cafarsite have been studied by Raman spectroscopy. DFT calculations enabled the position of AsO22- symmetric stretching mode at 839 cm-1, the antisymmetric stretching mode at 813 cm-1, and the deformation mode at 449 cm-1 to be calculated. The Raman spectrum of leiteite shows bands at 804 and 763 cm-1 assigned to the As2O42- symmetric and antisymmetric stretching modes. The most intense Raman band of leiteite is the band at 457 cm-1 and is assigned to the ν2 As2O42- bending mode. A comparison of the Raman spectrum of leiteite is made with the arsenite minerals reinerite and cafarsite.

Raman spectroscopic study of the uranyl titanate mineral betafite (Ca,U)2(Ti,Nb)2O6(OH) –Effect of Metamictization

Raman spectra of the uranyl titanate mineral betafite were obtained and related to the mineral structure. A comparison is made with the spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the (UO2)2+ stretching and bending vibrations, U-OH bending vibrations, H2O and (OH)- stretching, bending and libration modes. U-O bond lengths in uranyls and O-H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of betafite are comparable with those of the uranyl oxyhydroxides. The mineral betafite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

The effect of metamictization on the Raman spectroscopy of the uranyl titanate mineral davidite (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38

Raman spectra of the uranyl titanate mineral davidite-(La) (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38 were analysed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U-OH bending vibrations, H2O and (OH)- stretching, bending and libration modes. U-O bond lengths in uranyls and O-H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of davidite-(La) are in harmony with those of the uranyl oxyhydroxides. The mineral davidite-(La) is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

Raman spectroscopic study of the uranyl titanate mineral brannerite (U,Ca,Y,Ce)2(Ti,Fe)2O6 –Effect of Metamictization

Raman spectra of the uranyl titanate mineral brannerite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U-OH bending vibrations, H2O and (OH)- stretching, bending and libration modes. U-O bond lengths in uranyls and O-H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of brannerite are in harmony with those of the uranyl oxyhydroxides. The mineral brannerite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

Raman spectroscopic study of the uranyl titanate mineral euxenite (Y,Ca,U,Ce,Th) (Nb,Ta,Ti)2O6

Raman spectra of the uranyl titanate mineral euxenite were analyzed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The obsd. bands are attributed to the Ti[n.63743]O and (UO2)2+ stretching and bending vibrations, as well as lattice vibrations of rare-earth ions. The Raman bands of euxenite are in harmony with those of the uranyl oxyhydroxides. The mineral euxenite is metamict as is evidenced by the intensity of the U[n.63743]O stretching and bending modes, which are of lower intensity than expected, and with bands that are significantly broader.

The catalytic role of an isolated-Ti atom in the hydrogenation of Ti-doped Al(001) surface : An ab initio density functional theory calculation

Recent work [S. Chaudhuri, J.T. Muckerman, J. Phys. Chem. B 109 (2005) 6952] reported that two Ti-substituted atoms on an Al(0 0 1) surface can form a catalytically active site for the dissociation of H2, but the diffusion barrier of atomic H away from Ti site is as high as 1.57 eV. By using ab initio density functional calculations, we found that two hydrogen molecules can dissociate on isolated-Ti atom doped Al(0 0 1) surface with small activation barriers (0.21 and 0.235 eV for first and second H2, respectively). Additionally, the diffusion barrier of atomic H away from Ti site is also moderate (0.47 eV). These results contribute further towards understanding the improved kinetics observed in recycling of hydrogen with Ti-doped NaAlH4.

The location of Ti atom in sodium alanate : an ab initio spin-polarised study

In this work, ab initio spin-polarised Density Functional Theory (DFT) calculations are performed to study the interaction of a Ti atom with a NaAlH4(001) surface. We confirm that an interstitially located Ti atom in the NaAlH4 subsurface is the most energetically favoured configuration as recently reported (Chem. Comm. (17) 2006, 1822). On the NaAlH4(001) surface, the Ti atom is most stable when adsorbed between two sodium atoms with an AlH4 unit beneath. A Ti atom on top of an Al atom is also found to be an important structure at low temperatures. The diffusion of Ti from the Al-top site to the Na-bridging site has a low activation barrier of 0.20 eV and may be activated at the experimental temperatures (∼323 K). The diffusion of a Ti atom into the energetically favoured subsurface interstitial site occurs via the Na-bridging surface site and is essentially barrierless.