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The effect of the synthesis conditions on the structure and phase transitions in Ln2(MoO4)3
Solid State Sciences ( IF 3.5 ) Pub Date : 2020-12-24 , DOI: 10.1016/j.solidstatesciences.2020.106518
V.V. Popov , A.P. Menushenkov , A.A. Yastrebtsev , A.Yu. Molokova , S.G. Rudakov , R.D. Svetogorov , N.A. Tsarenko , K.V. Ponkratov , N.V. Ognevskaya , O.N. Seregina

The effect of the lanthanide cation type and calcination temperature on the structure and phase transitions in Ln2(MoO4)3 molybdates was studied using synchrotron X-ray diffraction, infrared and Raman spectroscopy, photoluminescence, simultaneous thermal analysis and inductively coupled plasma atomic emission spectroscopy. It was found that the crystallization of the precursors at 500 C/3 h results in the formation of nanocrystalline powders with the monoclinic structure (sp. gr. I112/b (15)) for Ln2(MoO4)3 (Ln = La–Ho), and a mixture of orthorhombic (sp. gr. Pnca(60)) and tetragonal (sp. gr. I41/a(88)) phases for Yb2(MoO4)3. A further increase in temperature to 1000 C leads to a significant rearrangement of the crystal structure, which is largely determined by the lanthanide type. The diagram of phase relations in the Ln2(MoO4)3 molybdates as a function of the Ln3+ cation radius and the calcination temperature has been refined. According to the results of Raman and IR spectroscopy, MoO4 tetrahedra are the main structural units in Ln molybdates. The increased hygroscopicity of heavy lanthanide molybdates (Ln = Ho, Yb) is associated with the presence of empty cavities in the orthorhombic structure. The photoluminescence spectra have shown that EuOn polyhedra in Eu2(MoO4)3 are distorted, and Eu3+ ions occupy several nonequivalent crystallographically different sites with a low symmetry point group.



中文翻译:

合成条件对Ln 2(MoO 43中结构和相变的影响

利用同步辐射X射线衍射,红外和拉曼光谱,光致发光,同时热分析和电感耦合等离子体原子发射研究了镧系元素阳离子类型和煅烧温度对Ln 2(MoO 43钼酸盐的结构和相变的影响光谱学。据发现,所述前体中的500结晶 C / 3小时导致形成纳米粉末的与单斜晶结构(比重=112 / b(15))为LN 2(的MoO 43LN =腊何),和斜方晶系的混合物(比重= Pnca(60))和四方(比重=4 1 /一个(88))相对于镱2(的MoO 43。进一步提高温度至1000 以下通入晶体结构,这在很大程度上是由镧系元素类型确定的显著重排。完善了Ln 2(MoO 43钼酸盐中作为Ln 3+阳离子半径和煅烧温度的函数的相关系图。根据拉曼光谱和红外光谱的结果,MoO 4四面体是钼酸镧的主要结构单元。重镧系钼酸盐(Ln  = Ho,Yb)的吸湿性增加与斜方晶结构中存在空洞有关。光致发光光谱表明,Eu 2(MoO 43中的EuO n多面体变形,并且Eu 3+离子占据了几个在晶体学上不等价的低对称点组的不同位点。

更新日期:2020-12-31
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