Question
Distinguish tetrahedral and octahedral voids.
| Sr. No. | Tetrahedral voids | Octahedral voids |
| 1. | A single triangular void in a crystal is surrounded by four (4) spheres and is called a tetrahedral void. | A double triangular void like c is surrounded by six (6) spheres and is called an octahedral void. |
| 2. | A sphere of second layer is above the void of the first layer, a tetrahedral void is formed. | The voids in the first layer are partially covered by the spheres of the layer. |
| 3. | This constitutes four spheres, three in the lower and one in the upper layer. When the centres of these four spheres are joined a tetrahedron is formed. | This constitutes six spheres, three in the lower layer and three in the upper layer. When the centers of these six spheres are joined an octahedron is formed. |
| 4. | The radius of the sphere which can be accommodated in an octahedral hole without disturbing the structure should not exceed 0.414 times that of the structure forming a sphere. | The sphere which can be placed in a tetrahedral hole without disturbing the close-packed structure should not have a radius larger than 0.225 times the radius of the sphere-forming the structure. |
| 5. | Radius of a tetrahedral void `"r"/"R"` = 0.225 | Radius of an octahedral void `"r"/"R"` = 0.414 |
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