Ahead of the lanthanide contraction; pressure and ionic size in the synthesis of MSr2RECu2O8 (RE = Rare Earth, M = Ru, Cr, Ir): a Gaussian relation.
Ahead of the lanthanide contraction; pressure and ionic size in the synthesis of MSr2RECu2O8 (RE = Rare Earth, M = Ru, Cr, Ir): a Gaussian relation.
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镧系元素收缩之前；
作者：
M. Alario;R. Ruiz;A. J. Dos santos
我们一直致力于在高压（P ≤ 12.5 Gpa）和高温（T ≤ 1400 K）下合成MSr 2 RECu 2 O 8（RE =稀土）类型的新材料，其形式上衍生自YBCO（即，CuBa 2 YCu 2 O 7）的结构，用[M-O 6]八面体（M = Ru，Cr或Ir）代替结构基面中的[Cu-O 4]正方形。这些铜酸盐作为主要相的充分形成只能在P和T的特定且相对窄的窗口中进行，在该窗口之外它们不能获得纯的或甚至根本不能获得。这些“最佳条件”承担显着的高斯相关性与稀土离子的大小，稀土阳离子在YBCO设置的晶胞的中心，他们不遵循经典的镧系收缩，所以经常观察到的化学元素。相反，电子间排斥似乎在固定合成条件中起着重要作用。此外，高斯尖端在压强-离子半径空间中的位置也取决于位于八面体中的过渡金属，这似乎与它们的简单氧化物的热力学稳定性有关。
We have been working for sometime on the synthesis at high pressure (P < or = 12.5 Gpa) and high temperature (T < or = 1400 K) of new materials of the type MSr2RECu2O8 (RE = Rare Earth), which formally derive from YBCO (i.e., CuBa2YCu2O7) by replacing the [Cu-O4] squares in the basal plane of the structure by [M-O6] octahedra (M = Ru, Cr or Ir). The adequate formation of these cuprates, as majority phases, can only be performed in a particular and relatively narrow window of P and T, outside which they cannot be obtained pure or even obtained at all. These "optimum conditions" bear a remarkable Gaussian correlation with the rare earth ion size, the rare earth cation being at the center of the unit cell in the YBCO setting, and they do not follow the classic lanthanide contraction so often observed in the chemistry of those elements. Instead, interelectronic repulsion seems to play a major role in fixing the synthesis conditions. Moreover, the position of the Gaussian tip in the pressure-ionic radii space is also dependent on the transition metal that sits in the octahedron, in a way that seems related to the thermodynamic stability of their simpler oxides.