Capsoni D, Bini M, Massarotti V, Mustarelli P, Belotti F, Galinetto P
Dipartimento di Chimica Fisica, M. Rolla dell'Università, viale Taramelli 16, 27100 Pavia.
J Phys Chem B. 2006 Mar 23;110(11):5409-15. doi: 10.1021/jp057088t.
The room temperature cation occupancy in LiMgVO(4) and LiZnVO(4) crystallographic sites is obtained by means of the combined use of X-ray powder diffraction (XRPD), (7)Li and (51)V magic angle spinning nuclear magnetic resonance (MAS NMR), and micro-Raman measurements. In the LiMgVO(4) Cmcm orthorhombic structure, the 4c (C(2)(v) symmetry) tetrahedral vanadium site is fully ordered; on the contrary, the Li 4c tetrahedral site and the 4b (C(2)(h) symmetry) Mg octahedral site display about 22% of reciprocal cationic exchange. Higher cationic disorder is observed in LiZnVO(4): the three cations can distribute on the three tetrahedral and distinct sites of the R-3 structure. XRPD and MAS NMR analysis results highly agree for what concerns vanadium ion distribution on the three cationic sites (about 25, 26, and 47%). From the full profile fitting of XRPD patterns with the Rietveld method, it is also obtained that Li(+) displays a slightly preferred occupation of the T1 position (approximately 55%) and Zn(2+) of the T2 position (approximately 46%). The vibrational spectra of the two compounds are characterized by different peak positions and broadening of the Raman modes, reflecting the cation distribution and the local vibrational unit distortion. A comparison is also made with recent Raman results on Li(3)VO(4). High temperature XRPD measurements rule out possible structural transitions up to 673 K for both compounds.
通过结合使用X射线粉末衍射（XRPD）、（7）Li和（51）V魔角旋转核磁共振（MAS NMR）以及显微拉曼测量，获得了LiMgVO(4)和LiZnVO(4)晶体学位点中的室温阳离子占有率。在LiMgVO(4)的Cmcm正交结构中，4c（C(2)(v)对称性）四面体钒位点是完全有序的；相反，Li 4c四面体位点和4b（C(2)(h)对称性）Mg八面体位点显示出约22%的相互阳离子交换。在LiZnVO(4)中观察到更高的阳离子无序性：三种阳离子可以分布在R-3结构的三个四面体和不同位点上。对于钒离子在三个阳离子位点上的分布（约25%、26%和47%），XRPD和MAS NMR分析结果高度一致。通过用Rietveld方法对XRPD图谱进行全谱拟合，还得出Li(+)对T1位置的占据略占优势（约55%），而Zn(2+)对T2位置的占据约为46%。这两种化合物的振动光谱的特征在于拉曼模式的不同峰位和展宽，反映了阳离子分布和局部振动单元畸变。还与最近关于Li(3)VO(4)的拉曼结果进行了比较。高温XRPD测量排除了这两种化合物在高达673 K时可能发生的结构转变。
