Structural behaviour of β-Cu2−δSe (δ = 0, 0.15, 0.25) in dependence on temperature studied by synchrotron powder diffraction
Structural behaviour of β-Cu2−δSe (δ = 0, 0.15, 0.25) in dependence on temperature studied by synchrotron powder diffraction
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DOI：
10.1016/j.jallcom.2005.10.079
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发表时间：
2006-09
影响因子：
6.2
通讯作者：
A. Skomorokhov;D. Trots;M. Knapp;N. N. Bickulova-N.;H. Fuess,
中科院分区：
文献类型：
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作者：
A. Skomorokhov;D. Trots;M. Knapp;N. N. Bickulova-N.;H. Fuess,
采用同步加速器粉末衍射和量热法在293 K <T<823 K范围内研究了超离子β-硒化铜β-Cu 2-δSe（δ=0，0.15，0.25）。Cu_（1.75）Se在室温下以超离子相存在，在600 K以下空气中稳定存在。Cu1.85Se在室温下以β相和α相的混合物存在，DCS实验中未检测到β+α→β相变，但在353 K时的衍射图中观察到纯β相; Cu1.85Se在空气中直到600 K仍保持稳定。铜释放过程在低于超离子-非超离子相变的温度下在Cu 2Se中开始。在T> 543 K时，成分接近Cu 1.95Se，并在573 K之前保持稳定。本文分析了β-Cu ~（2-）δSe在空气中存在的整个温度范围内的时均结构。面心立方晶胞（空间群Fm 3 <$m）由分布在八面体空隙（1/3<x<1/2）内四面体8（c）和32（f）（x，x，x）分裂位置的硒阴离子和铜阳离子形成。32（f）位的铜占有率随温度增加而增加，同时在8（c）位减少。此外，32（f）晶格位置的铜占据率也随着总铜含量2-δ而增加。提出了一种移动的Cu离子沿着四面体位置的扩散途径，即通过八面体空腔的外围沿“偏斜”的100 μ m方向扩散。
Superionic β-copper selenide, β-Cu2−δSe (δ=0, 0.15, 0.25), has been studied by synchrotron powder diffraction and calorimetric methods in the range 293K<T<823K. Cu1.75Se exists in the superionic phase at room temperature and remains stable in air up to 600K. Cu1.85Se exists at room temperature as a mixture of β and α phases, β+α→β phase transition is not detected in DCS experiment, however, pure β-phase was observed in diffraction pattern of Cu1.85Se at 353K; Cu1.85Se remains stable in air up to 600K. A copper release process starts in Cu2Se at a temperature below the superionic–non-superionic phase transition. At T>543K the composition is close to Cu1.95Se and remains stable up to 573K. Time average structure of β-Cu2−δSe has been analysed in the whole temperature range of existence in air. A face centred cubic unit cell (space group Fm3¯m) is formed by the selenium anions with copper cations distributed over tetrahedral 8(c) and 32(f) (x, x, x) split positions within the octahedral voids (1/3<x<1/2). The copper occupancy of the 32(f) sites increases with temperature with a simultaneous decrease in the 8(c) sites. Besides, the copper occupancy of the 32(f) lattice site also increases with the total copper content 2−δ. A diffusion pathway of mobile Cu ions along the tetrahedral sites, in “skewed” 〈100〉 directions through the peripheries of octahedral cavities is proposed.