Why amorphous solids are isotropic

Improve this answer. Divyansh Jain Divyansh Jain 96 2 2 bronze badges. Structural birefringence in amorphous solids Abstract: The result reported in an earlier investigation with vitreous silica is now shown to be true also for other amorphous solids, including especially inorganic glasses; besides the well-known photo-elastic effect, another kind of birefringence may be observed differing from the former both in its origins and in its observable characters.

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Related Wiki. Offered for classes , LearnNext is a popular self-learning solution for students who strive for excellence. Crystalline solids are callled anisotropic i.

Amorphous solids are said to be isotropic, and crystalline solids are anisotropic for their physical property measurements. Isotropy comes from the Greek word; iso means same and tropos means direction. Due to the some regular arrangement of atoms and molecules in all directions the physical properties do change in the opposite direction.

And we already know that the isotropic solids have the same physical properties in all the directions. Thus we can say that crystalline solids are not isotropic.

Crystalline solids have well-defined edges and faces, diffract x-rays, and tend to have sharp melting points. In contrast, amorphous solids have irregular or curved surfaces, do not give well-resolved x-ray diffraction patterns, and melt over a wide range of temperatures. Nearly all single crystal systems are anisotropic with respect to mechanical properties, with Tungsten being a very notable exception, as it is a cubic metal with stiffness tensor coefficients that exist in the proper ratio to allow for mechanical isotropy.

In a single crystal, the physical and mechanical properties often differ with orientation. When a material is formed, the grains are usually distorted and elongated in one or more directions which makes the material anisotropic. Due to the random arrangement, the distribution of particles would be widely different along each axis. Hence, an average value of the measurement is taken.

But what if the crystalline solid has an equal perfect distribution of atoms in a unit cell like in a cubic structure, then would it be isotropic for all the properties?

The answer is no. A perfectly arranged cubic crystal structure would be isotropic for some properties like refractive index but would be anisotropic for other properties like photoelasticity. Therefore, in general, we can say that all crystalline solids are anisotropic for some of their physical properties and all amorphous solids are isotropic.

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