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Ch.12 - Solids and Modern Materials
Chapter 12, Problem 105

Imagine the primitive cubic lattice. Now imagine pushing on top of it, straight down. Next, stretch another face by pulling it to the right. All angles remain 90°. What kind of primitive lattice have you made?
Illustration showing transformation of a simple cubic unit cell under pressure and stretching.

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Step 1: Identify the initial structure as a primitive cubic lattice, where all sides are equal, and all angles are 90°.
Step 2: Apply pressure from the top, which compresses the lattice along one axis, reducing the height of the unit cell.
Step 3: Stretch the lattice by pulling one face to the right, which increases the length of the unit cell along that axis.
Step 4: Observe that all angles remain 90°, but the unit cell now has different lengths along the three axes.
Step 5: Conclude that the resulting lattice is a tetragonal lattice, characterized by two equal axes and one different axis, with all angles remaining 90°.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Primitive Cubic Lattice

A primitive cubic lattice is a type of crystal structure where atoms are located at the corners of a cube. Each unit cell contains one atom, as the corner atoms are shared among adjacent cells. This lattice is characterized by its simple geometry and is the basis for understanding more complex structures.
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Deformation of Lattices

Deformation of lattices refers to the changes in the arrangement of atoms in a crystal structure due to external forces, such as pressure or tension. In this scenario, pushing down on the lattice compresses it, while pulling on a face stretches it, resulting in a new arrangement of atoms while maintaining right angles between the axes.
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Types of Crystal Systems

Crystal systems categorize crystals based on their symmetry and lattice parameters. The transformation described in the question leads to a body-centered cubic (BCC) structure, where an additional atom is added to the center of the cube, resulting in a more complex arrangement while preserving the cubic symmetry.
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