ANION VOIDAGE AND THE VOID SUPERLATTICE IN ELECTRON-IRRADIATED CAF2
ANION VOIDAGE AND THE VOID SUPERLATTICE IN ELECTRON-IRRADIATED CAF2
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DOI：
10.1080/00337578308207404
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发表时间：
1983-01-01
影响因子：
1
通讯作者：
CHADDERTON, LT
中科院分区：
文献类型：
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作者：
JOHNSON, E;CHADDERTON, LT
通过原位透射电子显微镜研究了电子辐照（100 keV-1 MeV）萤石（CaF2）中的阴离子空隙和阴离子空隙晶格的形成。在低能量密度 (≲1 dpa) 下，损伤由随机分布的阴离子空洞和与氟气相关的大气泡状缺陷组成。在较高的注量 (≳ 1 dpa) 下，阴离子空隙形成具有简单立方结构的三维有序超晶格，其轴与基体的轴相称。超晶格的晶胞参数A0在15-30 nm范围内，比率A0/R（超晶格参数/阴离子空隙半径）在3-6范围内。完全有序的超晶格通过有序过程从随机分布的阴离子空洞中“结晶”，其中局部有序区域以类似于外延的方式生长在一起，在各个完全有序的块之间留下扭曲的超晶格区域。基本辐射损伤事件是辐射分解的，并局限于阴离子亚晶格。阴离子亚晶格上的损伤过程和缺陷行为，由未受影响的阳离子亚晶格被动稳定，导致阴离子空隙和阴离子空隙晶格形成，因此可以被认为类似于金属中的空隙过程。萤石中的阴离子空隙率与金属中的空隙率之间的密切相关性通过在 330 K 以上辐照下的萤石中观察到的大面阴离子空隙进一步强调。通常用于解释金属中空隙晶格稳定性的基于弹性空隙-空隙相互作用的理论不适用于萤石中的简单立方阴离子空隙晶格，其形成只能用 Foreman 的机制来解释。在该模型中，沿着密排行具有过度移动性的拥挤间隙产生了一个上部结构，其中空隙也沿着密排行排列，每个空隙都保护其相邻空隙免受间隙捕获。有人认为萤石中的各向异性间隙通量是由 VK 中心提供的，其结构是沿着密排阴离子行延伸的 F2−分子。据设想，萤石中的线性扩散VK中心能够在衰变成阴离子弗伦克尔对之前非常接近阴离子空隙，并且阴离子填隙注入阴离子空隙中的概率增加，从而提供福尔曼模型所需的填隙类型缺陷。
Anion voidage and anion void lattice formation in electron irradiated (100 keV–1 MeV) fluorite (CaF2) has been investigated byin situtransmission electron microscopy. At low fluences (≲1 dpa) the damage consists of randomly distributed anion voids and large bubble-like defects associated with fluorine gas. At higher fluences (≳ 1 dpa) the anion voids form a three-dimensional ordered superlattice with asimple cubicstructure, whose axes are commensurate with those of the matrix. The superlattice has a unit cell parameterA0in the range 15–30 nm and a ratioA0/R(superlattice parameter/anion void radius) in the range 3–6. The fully ordered superlattice “crystallizes” from randomly distributed anion voids by an ordering process in which locally ordered areas grow together after a fashion similar to that of epitaxy, leaving distorted superlattice regions between individual, fully ordered blocks.The basic radiation damage events are radiolytic and confined to the anion sublattice. Damage processes and defect behaviour on the anion sublattice, passively stabilized by the unaffected cation sublattice, leading to anion voidage and anion void lattice formation, can hence be considered analogous to voidage processes in metals. This close correlation between anion voidage in fluorite and voidage in metals is further emphasized by the observation of large faceted anion voids in fluorite irradiated above 330 K.Theories based on elastic void-void interactions normally used to explain void lattice stabilization in metals are inapplicable to the simple cubic anion void lattice in fluorite, the formation of which can only be explained in terms of a mechanism due to Foreman. In this model crowdion interstitials having an excess of mobility along close-packed rows give rise to a superstructure where the voids are also arranged along close-packed rows, each void shielding its neighbours from interstitial capture. It is suggested that the anisotropic interstitial flux in fluorite is provided byVKcentres, which structurally are F2−molecules extended along the close-packed anion rows. It is envisaged that the linearly diffusingVKcentres in fluorite are capable of approaching very close to the anion voids before decaying into anion Frenkel pairs with enhanced probability of injection of anion interstitials into the anion voids, thus providing the interstitial type defect required by Foreman's model.