Vibrational modes and structure of lanthanide fluoride–potassium fluoride binary melts LnF3–KF (Ln=La, Ce, Nd, Sm, Dy, Yb)
Vibrational modes and structure of lanthanide fluoride–potassium fluoride binary melts LnF3–KF (Ln=La, Ce, Nd, Sm, Dy, Yb)
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DOI：
10.1039/a802812e
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
V. Dracopoulos;B. Gilbert;G. Papatheodorou
中科院分区：
文献类型：
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作者：
V. Dracopoulos;B. Gilbert;G. Papatheodorou
测量了一系列LnF_3-KF（Ln=La，Ce，Nd，Sm，Dy，Yb）二元熔体混合物的拉曼光谱，温度为1000°C，组成为40 mol.%对于具有La和Ce且至多25摩尔%的混合物，剩下的混合物。结果表明，当摩尔分数为XLnF_3 ≤ 0.25时，LnF_（63）八面体是主要组分，产生两个主带，一个是极化带，另一个是去极化带，分别归属于八面体的ν_1（A_1g）和ν_5（F_2g）振动模。在445 cm-1（Yb）~ 400 cm-1（La）范围内，ν1频率随镧系阳离子极化率的增加几乎呈线性变化。这种变化尚未观察到在相应的二进制熔体涉及氯化物和溴化物，有人认为，由阴离子的Ln 3+的相对屏蔽是负责这种行为。当摩尔分数XLnF_3>0.25时，还原的各向同性和各向异性光谱特征与YF_3-KF（V. Dracopoulos，B.吉尔伯特，B。Borresen，G. Photiadis和G. N. Papatheodorou，J. Chem. Soc.，FaradayTrans.，1997，93，3081）。一个极化和两个去极化带出现在光谱中的解释表明，在这些熔体中的主要振动产生从扭曲的LnF 63-八面体约束常见的氟化物（边缘共享）。各向异性散射强度被发现增加，相对于各向同性强度，与镧系阳离子的大小和摩尔分数的增加。这种不寻常的效果是由于偶极诱导偶极的熔体中的阳离子之间的相互作用和它的变化从系统到系统是有关的Ln 3+阳离子的大小和极化率和它的相对屏蔽的F-阴离子。
Raman spectra of a series of LnF3–KF (Ln=La, Ce, Nd, Sm, Dy, Yb) binary melt mixtures have been measured at temperatures up to 1000°C and at compositions up to 40 mol.% for the mixtures with La and Ce and up to 25 mol.% for the remaining mixtures. The data indicate that at mole fractions XLnF3⩽0.25 the LnF63- octahedra are the predominant species giving rise to two main bands, one polarized, the other depolarized, which are assigned to the ν1(A1g) and ν5(F2g) vibrational modes of the octahedra, respectively. The ν1 frequency varies almost linearly with the polarizing power of the lanthanide cation increasing from 445 cm-1 (Yb) to 400 cm-1 (La). Such a variation has not been observed in the corresponding binary melts involving chlorides and bromides; it is argued that the relative shielding of the Ln3+ by the anions are responsible for this behaviour. At mole fractions XLnF3>0.25 the features of the reduced isotropic and anisotropic spectra are similar to those of the YF3–KF (V. Dracopoulos, B. Gilbert, B. Borresen, G. Photiadis and G. N. Papatheodorou, J. Chem. Soc., FaradayTrans., 1997, 93, 3081). One polarized and two depolarized bands appear in the spectra which are interpreted to indicate that the predominant vibrations in these melts arise from distorted LnF63- octahedra bound by common fluorides (edge sharing). The anisotropic scattering intensity was found to increase, relative to the isotropic intensity, with both increasing the size and mole fraction of the lanthanide cation. This unusual effect is attributed to dipole-induced-dipole interactions between cations in the melt and its variation from system to system is related to the size and polarizability of the Ln3+ cation and its relative shielding by the F- anions.