# hcp crystal structure

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Therefore, total number of In the three-dimensional crystal structure, unit cell is characterized by –. number of atoms surrounding the central atom, for hcp structure is 12. atoms contributes ½ of its part to one unit cell. of all the six atoms in the unit cell, The It’s the natural way for humans to pack spheres. It turns out that face-centered cubic and hexagonal close-packed crystal structures pack atoms equally tightly. Using this understanding, we can compute the number of atoms per unit cell in a hcp structure as below: Number of atoms fully contributing to the unit cell = 3 (all in the middle layer), Number of atoms contributing ½ to the unit cell = 2 (1 in top and 1 in bottom layer, respectively), Number of atoms contributing 1/6 to the unit cell = 12 (6 in top and 6 in bottom layer, respectively), Total number of atoms in the unit cell = 3 + ½ x 2 + 1/6 x 12 = 3+1+2= 6. atoms. Pro Lite, Vedantu Pro Lite, Vedantu calculate the number of atoms per unit cell, first consider the bottom layer. (BS) Developed by Therithal info, Chennai. The John A. Dutton e-Education Institute is the learning design unit of the College of Earth and Mineral Sciences at The Pennsylvania State University. has to be noted that, each and every corner atom touches with each other, Except where otherwise noted, content on this site is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. We have shown the hcp structure diagram in the previous section. Let us know that ‘c’ is the height of the unit cell of HCP structure and ‘a’ is the The College of Earth and Mineral Sciences is committed to making its websites accessible to all users, and welcomes comments or suggestions on access improvements. atom has 6 neighboring atom in its own plane. In the top and bottom layers, the base centered atom is surrounded by six corner atoms. Contact Us, Privacy & Legal Statements | Copyright Information In We can compute the volume of a unit cell using these 2 parameters as follows: Volume of Hcp Unit Cell=  $\frac{3\sqrt{3}a^{2}c}{2}$. The central sphere or atom in top and bottom layers is shared with 1 other unit cell, hence they only contribute ½ to one unit cell. bottom face of the hexagon, in alternate vertical faces. Luckily, it’s still relatively easy to visualize. It Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail. If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. volume of the unit cell of the HCP = base area x height. bottom face of the hexagon. We can accurately predict the arrangement of particles of another region, if we know the arrangement of particles in one region of the crystal. The series for this lattice structure can also be written as …..-a-b-a-b-a-b-…..and so on. the packing density is 74% and hence, it is a closed packed structure. Solid materials show specific crystal structures. It turns out that face-centered cubic and hexagonal close-packed crystal structures pack atoms equally tightly. Hence, one unit cell of hcp structure comprises 6 atoms. corner atoms, one at each and every corner of the Hexagon. The atoms at the hexagonal vertices in top and bottom layers are shared with 5 other unit cells, hence they contribute just 1/6 to one unit cell. In fact, it is a simpler structure. atoms are situated inside the face so that they can’t be shared by other cells The Pennsylvania State University © 2020, Hexagonal close-packed structure unit cell, Academic Integrity and Citation Style Guide, Lesson 2: Economic, Environmental, and Societal Issues in Materials Science, Lesson 5: Structure and Applications of Metals. The hcp structure is considered to have three layers viz, 1) Bottom Layer [B1],2) Top Layer [T1] and 3) Middle Layer [M1] as shown. This ends our coverage on the topic “Hexagonal Close Packing”.