Thus, a unit cell is characterized by six parameters a, b, c, α , β and γ. Hexagonal close packing, or hcp in short, is one of the two lattice structures which are able to achieve the highest packing density of ~74%, the other being face centered cubic (fcc) structure. and every corner atom contributes 1/6 of its part to one unit cell. We hope you enjoyed learning and were able to grasp the concepts. This ends our coverage on the topic “Hexagonal Close Packing”. Vedantu academic counsellor will be calling you shortly for your Online Counselling session. as shown in the figure .1.10, (i)                Credit: Callister & Rethwisch 5e. Hexagonal close packing, or hcp in short, is one of the two lattice structures which are able to achieve the highest packing density of ~74%, the other being face centered cubic (fcc) structure. Hexagonal Close Packed Crystal Structure (HCP), Video Assignment: Metal: The Secret Life of Material, Lesson 6: Types and Applications of Metal Alloys, Lesson 7: Structure and Applications of Ceramics, Lesson 8: Structure and Applications of Polymers, Lesson 9: Types and Applications of Composites, Lesson 10: Synthesis, Fabrication, and Processing of Materials, Lesson 11: Biomaterials and Smart Materials, Lesson 12: Semiconductors and Nanomaterials, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, Department of Energy and Mineral Engineering, Department of Materials Science and Engineering, Department of Meteorology and Atmospheric Science, Earth and Environmental Systems Institute, iMPS in Renewable Energy and Sustainability Policy Program Office, BA in Energy and Sustainability Policy Program Office, 2217 Earth and Engineering Sciences Building, University Park, Pennsylvania 16802. The face-centered volume of the unit cell of the HCP = base area x height. Please proceed to your e-textbook and read the first chapter of this lesson’s assigned reading. If you look at the figure below, you might think that hexagon close-packed crystal structure is more complicated than face-centered cubic crystal structure. Pro Lite, CBSE Previous Year Question Paper for Class 10, CBSE Previous Year Question Paper for Class 12. Its dimensions along the three edges a, b and c. These edges may or may not be mutually perpendicular. It turns out that face-centered cubic and hexagonal close-packed crystal structures pack atoms equally tightly. 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. Solid materials show specific crystal structures. Thus In this section, we will discuss the hcp unit cell in a little more detail. The amount of space occupied is given by the formula \[\frac{π}{3\sqrt{2}}\] which approximately translates to 0.74048. Number A crystalline solid consists of a large number of small crystals, each of them having a definite characteristic geometrical shape. has to be noted that, each and every corner atom touches with each other, 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. In the hcp structure of an unit cell contains three types of atoms as three layers. bottom face of the hexagon. of atoms per unit cell, To In these crystals, arrangement of constituent particles is in order and repetitive in three dimensions. the number of atoms present in the upper layer is 1 + ½ = 3/2, The Top Layer [T1] and 3) Middle Layer [M1] as shown. atom contributes ½ of its part to one unit cell. structure of an unit cell contains three types of atoms as three layers. It’s the natural way for humans to pack spheres. total number of atoms present in the unit cell = 3/2 + 3/2 + 3  = 6 atoms. This packing structure is found in metals such as zinc, cadmium, cobalt and titanium. corner atoms, one at each and every corner of the Hexagon. In the middle layer we have 3 atoms stacked inside the unit cell as The coordination number, i.e. coordination number of the hcp structure can be calculated as follows. Why Did it Take So Long Between the Bronze Age and the Iron Age? Please send comments or suggestions on accessibility to the site editor. middle layer (ML2) of unit cell -2. In Copyright © 2018-2021 BrainKart.com; All Rights Reserved. Angles between the edges, α (between b and c), β (between a and c) and γ (between a and b). The series for this lattice structure can also be written as …..-a-b-a-b-a-b-…..and so on. atoms are situated inside the face so that they can’t be shared by other cells atoms. The shape of the unit cell of a hexagonal close packed lattice structure is a hexagonal prism.