Design of hard crystals
Design of hard crystals
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DOI：
10.1016/j.ijrmhm.2005.05.015
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发表时间：
2006-01-01
影响因子：
3.6
通讯作者：
Kaner, RB
中科院分区：
文献类型：
--
作者：
Gilman, JJ;Cumberland, RW;Kaner, RB
硬度是通过在固体上压痕或刮擦来测量的。一般来说，它是结构稳定性的量度，而结构稳定性又由弹性刚度、塑性阻力、结构变化阻力决定;所有这些都随化学键合类型（电子结构）而变化。为了获得最大硬度，必须同时最大化关键性能。此外，硬度是一种三维性质，因此必须在三维空间中最大化这些性质。抗弹性应变主要取决于价电子体积密度VED（电子/单位体积）。对于sp键，价电子的数量简单地等于周期表的列数（I，II，III或IV）。对于过渡元素，没有可靠的规则。体积模量随VED的增大而增大，剪切模量则更为复杂，塑性变形抗力主要取决于位错的运动。这是由共价键合固体（半导体）中的内在因素和金属中的外在因素决定的。当位错移动时，其核心的原子对称性发生变化。这对sp-bonded金属影响不大，但它深刻地影响了共价晶体中的化学键合。为了获得最大的硬度，必须将位错的迁移率降到最低。上述原理已被应用于创造一种新的材料，很容易划伤蓝宝石;即OsB 2。据信，它们可以用来制造更硬的材料。(c)2005爱思唯尔有限公司保留所有权利。
Hardness is measured by indenting, or by scratching, a solid. In general, it is a measure of structural stability which, in turn, is determined by elastic stiffness, plastic resistance, resistance to structure change; all of which vary with chemical bonding type (electronic structure). For maximum hardness, the key properties must be simultaneously maximized. Furthermore, hardness is a three-dimensional property, so the properties must be maximized in three-dimensions.Resistance to elastic strain depends primarily on valence-electron volumetric density, VED (electrons/unit volume). For sp bonding, the number of valence electrons simply equals the column number (I, II, III, or IV) of the Periodic Table. For the transition elements, there is no reliable rule. The bulk modulus increases with the VED, while the shear moduli are more complex.Resistance to plastic deformation depends primarily on dislocation mobility. This is determined by intrinsic factors in covalently bonded solids (semiconductors) and by extrinsic factors in metals. When a dislocation moves, the atomic symmetry at its core changes. This has a little effect in sp-bonded metals, but it profoundly affects the chemical bonding in covalent crystals. For maximum hardness, dislocation mobility must be minimized.The above principles have been applied to create a new material that easily scratches sapphire; namely, OsB2. It is believed that they can be used to create even harder materials. (c) 2005 Elsevier Ltd. All rights reserved.