CRYSTALLOGRAPHIC SHEAR IN MOLYBDENUM TRIOXIDE
CRYSTALLOGRAPHIC SHEAR IN MOLYBDENUM TRIOXIDE
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DOI：
10.1098/rspa.1969.0118
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发表时间：
1969-01-01
影响因子：
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通讯作者：
BURSILL, LA
中科院分区：
文献类型：
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作者：
BURSILL, LA
三氧化钼的薄样品在电子显微镜中加热后，在{120}面上产生平面缺陷。用电子衍射的双束理论（包括吸收）解释这些缺陷为不连续面，其中相邻的MoO_3型结构的板相对于彼此位移了位移矢量R = ±½a+1/7 b。这些“剪切”平面是化学缺陷，因为在剪切发生之前必须去除氧原子。剪切平面的密度使得非化学计量范围MoO 3-x（0 <x< 0.05）可以被描述为无序剪切结构，由此MoO 3型基质被不规则间隔的剪切平面中断，其密度、面积和取向根据样品的确切组成而变化。可以观察到剪切平面在中间相的区域内成核和生长。畴的晶体结构的研究，除了选定的区域衍射使用的弯曲消光轮廓在畴界和暗场观察的位移。从电子显微照片中估算了MoO 2.9975的组成作为畴结构。一个7 × 7的MoO 3超晶格的氧空位推导出的域结构。这些观察结果为非化学计量范围MoO 3-x（0 <x< 0.05）的缺陷的性质、分布和产生机制提供了直接证据。根据我们的观察，讨论了三氧化钼热分解和无序剪切结构产生的模型。后者与最近在文献中提出的三个相互冲突的模型进行了比较，没有直接的实验证据，在非化学计量的过渡金属氧化物的有序和无序的剪切结构的生产机制。
Thin specimens of molybdenum trioxide, after heating in the electron microscope, develop planar defects on {120} planes. The two beam theory of electron diffraction including absorption is used to interpret these defects as planes of discontinuity where neighbouring slabs of MoO3type structure are displaced relative to each other by the displacement vectorsR= ±½a+1/7b. These ‘shear’ planes are chemical defects since oxygen atoms must be removed before the shear can occur. The density of shear planes is such that the non-stoichiometric range MoO3-x(0 <x< 0.05) may be described as a disordered shear structure whereby the MoO3type matrix is interrupted by irregularly spaced shear planes whose density, area and orientation vary according to the exact composition of the specimen. The shear planes may be observed to nucleate and grow within domains of an intermediate phase. The crystal structure of the domains is studied using the displacement of bend extinction contours at the domain boundaries and dark field observations in addition to selected area diffraction. The composition MoO2.9975is estimated for the domain structure from the electron micrographs. A 7 x 7 MoO3superlattice of oxygen vacancies is deduced for the domain structure. These observations provide direct evidence of the nature, distribution and mechanism of production of the defects responsible for the non-stoichiometric range MoO3-x(0 <x< 0.05). On the basis of our observations models for the thermal decomposition of molybdenum trioxide and for the production of the disordered shear structure are discussed. The latter is compared with three conflicting models recently proposed in the literature, without direct experimental evidence, for the mechanism of production of ordered and disordered shear structures in non-stoichiometric transition metal oxides.