碱金属钨酸盐晶体与熔体微结构与特征拉曼振动波数的相关性

The Correlation between the Micro-structure and Characteristic Raman-Active Vibrational Wavenumber of the Crystalline and Molten Alkali Tungstates

本文选取了5种锂钨酸盐晶体结构,搭建了8种含Na+阳离子的团簇模型,并分别基于MS(materials studio)软件的CASTEP(cambrigde serial total energy package)模块和Gaussian09软件对其拉曼振动波数和散射活性进行了DFT(密度泛函理论)计算。通过分析,发现晶体中W-Onb(non-bridging oxygen,即非桥氧)键对称伸缩振动波数随其键长的减小而增大,在熔体中也存在类似关系。为反映局部应力对W-Onb键对称伸缩振动波数的影响,在本工作中分别对晶体和熔体中的微结构进行了指认。结果表明,在Li_2O-WO_3二元系中,构成晶体的主要阴离子基团为[WO_6]^(6-),且该基团W-Onb键的对称伸缩振动波数随着桥氧数的增大而增大;在熔体中W-Onb键的对称伸缩振动波数一般为[WO_4]^(2-)>[WO_5]^(4-)>[WO_6]^(6-),且当W-O基团确定后,该振动波数会随着桥氧数的增大而增大。该相关性有助于碱金属钨酸盐晶体及熔体结构中阴离子基团的诊断与鉴别。本文测定了A2WnO3n+1(A=Li,Na,K;n=1,2,3)共9种成分熔体的原位拉曼光谱,以验证该相关性。

Five different kinds of crystalline structures in the Li 2O-WO 3 binary system were selected and an ensemble of eight cluster models containing Na+cation was built in this paper.DFT(density functional theory)calculation of their Raman-active vibration wavenumbers together with scattering activities were performed based on MS(materials studio)CASTEP(cambrigde serial total energy package)program and Gaussian09 code,respectively.The wavenumbers of W-O nb(non-bridging oxygen)Raman symmetric stretching vibration modes were found to increase with the decrease of W-O nb bond length not only for crystals but also for melts.In order to reflect the influence of local stress on the wavenumber of W-O nb symmetric stretching vibration mode,the micro-structures in crystals and melts were identified,respectively.Results show that bulk crystals usually contain[WO 6]6-coordinated groups in the Li 2O-WO 3 binary system,the wavenumber of W-O nb symmetric stretching vibration mode in[WO 6]6-will increase with the increase of the number of bridging oxygen;while in the melt,the wavenumber of W-O nb symmetric stretching vibration mode generally follows:[WO 4]2->[WO 5]4->[WO 6]6-.When the W-O group is determined,this wavenumber will increase with the increase of the number of bridging oxygen.The correlation is helpful for the diagnosis and identification of the anion groups in the crystalline and molten alkali tungstate compounds.The in-situ Raman spectra of molten A 2W nO 3n+1(A=Li,Na,K;n=1,2,3)have been measured in order to verify the correlation obtained in this paper.