Glass-Ceramics Containing Nano-Crystallites of Oxide Semiconductor
Glass-Ceramics Containing Nano-Crystallites of Oxide Semiconductor
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DOI：
10.5772/intechopen.83927
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发表时间：
2010-09
期刊：
影响因子：
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通讯作者：
H. Masai;Y. Takahashi;T. Fujiwara
中科院分区：
文献类型：
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作者：
H. Masai;Y. Takahashi;T. Fujiwara
1.1玻璃和水晶无机玻璃材料一般具有高透明度、良好的成型性和可调节的化学成分范围。由于玻璃没有晶界，这是液体的一个特点，获得高透明度的玻璃使其成为人们日常生活中的基本材料，如窗户、显示面板玻璃和光学玻璃纤维。良好的成形性源于无间隙体积的无规则网络结构，因此可以比无机晶体更容易制备出大而长的玻璃材料。请注意，玻璃中的“随机”一词意味着缺少长程有序。实际上，玻璃中存在构成各种配位多面体的原子的短程有序。因此，非晶的短程有序与晶体的短程有序化基本相同。另一方面，玻璃的随机网络与化学成分的多样性密切相关，这反过来又允许我们定制物理性质和各种功能。这种多样性也是非晶态玻璃材料的一个独特特点。玻璃最传统的定义是“一种具有玻璃化转变行为的非晶态材料”。图1显示了玻璃和晶体的典型体积随温度的变化。对于晶体，从液体到凝固的转变发生在熔化温度Tm。另一方面，玻璃材料在Tm以下处于过冷态，在玻璃粘度增加到1013dpa·S的温度范围内发生向玻璃的转变，发生过冷液向玻璃转变的温度称为玻璃化转变温度Tg。在温度范围内，玻璃材料的某些物理参数呈现出“有些陡峭”的变化。由于Tg是一个虚构的温度，取决于制造过程，所以一个玻璃可以有几个Tg的值，取决于冷却速度。如图1所示，晶体和玻璃之间存在体积差，这源于玻璃材料具有随机网络的自由体积。由于随机网络结构，玻璃材料的吉布斯自由能固有地大于相应晶体的吉布斯自由能，玻璃材料以亚稳态存在。这意味着玻璃向晶相的相变可以在Tg以上进行，在Tg时组成单元2的迁移
1.1 Glass and Crystal Inorganic glass materials generally possess high transparency, good formability, and tuneable chemical composition range. Since glass has no grain boundary, which is a characteristic of liquid, attained high transparency of glass makes it to be a fundamental material for our daily life, for examples, window, display panel glass and optical glass fibres. The good formability is originated from the random network structure with interstitial free volume, and therefore, large and long glassy material can be prepared much easier than inorganic crystal. Note that the term “random” in glass means a lack of the longrange ordering. Actually in glass there is a short-range ordering of atoms that constitute various coordination polyhedra. Thus, the short-range ordering in amorphous is basically identical to that in crystal. On the other hand, the random network of glass closely correlates with the chemical composition diversity, which in turn allows us to tailor physical property and various functionalities. The diversity is also a unique characteristic of amorphous glass materials. The most conventional definition of glass is ′′an amorphous material possessing the glass transition behaviour”. Figure 1 shows a typical volume change of glass and crystal as a function of temperature. In the case of crystal, transition from liquid to solidified crystal occurs at the melting temperature, Tm. On the other hand, a glass material takes the supercooled state below the Tm, and shows the transition to glass in the temperature range where the viscosity of glass increases to 1013 dPa·s. Temperature at which transition from supercooled liquid to glass occurs is mentioned as the glass transition temperature, Tg. In the temperature region, some physical parameters of glass material show “some steep” change. Since the Tg is a fictive temperature that depends on the fabrication process, a glass can take several values of Tg depending on the cooling rate. As shown in Fig. 1, there is a volume difference between crystal and the glass, which originates from the free volume of glass material possessing the random network. Because of the random network structure, the Gibbs free energy of a glass material is inherently larger than that of the corresponding crystal, and glass materials exist as a metastable state. It means that phase transition of glass to crystalline phase can progress above the Tg, at which migration of the compositional units 2