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Questions and Answers
What is crystal structure?
What is crystal structure?
A description of the ordered arrangement of atoms, ions, or molecules in a crystalline material.
What is the chemical formula for strontium titanate?
What is the chemical formula for strontium titanate?
SrTiO3
How many atoms are present in a simple cubic unit cell?
How many atoms are present in a simple cubic unit cell?
What is the packing efficiency of a body-centered cubic lattice?
What is the packing efficiency of a body-centered cubic lattice?
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Polymorphism is the ability of a solid material to exist in more than one form.
Polymorphism is the ability of a solid material to exist in more than one form.
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What are crystal defects?
What are crystal defects?
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What relates to allotropy?
What relates to allotropy?
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The packing efficiency for a face-centered cubic lattice is ____%.
The packing efficiency for a face-centered cubic lattice is ____%.
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Study Notes
Crystal Structure
- Crystal structure describes the ordered arrangement of atoms, ions or molecules in a crystalline material.
- Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids.
- A crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure.
- The smallest group of particles in the material that constitutes the repeating pattern is called the unit cell.
- The unit cell completely defines the symmetry and structure of the entire crystal lattice, which is built up by repetitive translation of the unit cell along its principal axes.
- The repeating patterns are said to be located at the points of the Bravais lattice.
Simple Cubic Lattice
- Coordination number = 6
- Packing Efficiency = 52%
- 1/8 atom at each of 8 corners
Body-centered Cubic Lattice
- Coordination number = 8
- Packing Efficiency = 68%
- 1 atom at the center of the unit cell
Face-centered Cubic Lattice
- Coordination number = 12
- Packing Efficiency = 74%
- 1/2 atom at each of the 6 faces
Summary of Cubic Lattices
- Simple Cubic: 1 atom per unit cell; Packing Efficiency = 52.4%; Empty Space = 47.6%
- Body-centered Cubic: 2 atoms per unit cell; Packing Efficiency = 68%; Empty Space = 32%
- Face-centered Cubic: 4 atoms per unit cell; Packing Efficiency = 74%; Empty Space = 26%
Defects in Crystals
- Crystal defect: an imperfection in the regular geometrical arrangement of the atoms in a crystalline solid.
- Defects can result from deformation of the solid, rapid cooling from high temperature, or high-energy radiation.
- Defects influence the mechanical, electrical, and optical behavior of the solid.
Polymorphism
- Polymorphism: the ability of a solid material to exist in more than one form or crystal structure.
- Polymorphism can be found in any crystalline material including polymers, minerals, and metals.
- Examples include glycine, calcite, and aragonite.
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