This slide is all about crystal structure such as unit cell, simple cubic unit cell, body-centered unit cell, and face-centered unit cell. Also, I explained Crystal defects such as line defects, planar defects, and point defects.

1. Gono
University
Submitted To
DR. SWAPWAN KUMAR SARKAR
Assistant Professor
Gono University
Contributing
Members: Group-2
► Sazzad Rahman (457)
► Fahima Rahman(458)
► Md Shahab Uddin(459)
► Mazharul Islam (460)
MPBME-324
Fundamental of
Biomaterials
Course Name
Course Name

2. Chapter : The Structure of
Solids
Topic : Crystal structure

3. 2
3 4
A crystal is a solid composed of atoms, ions,
or molecules arranged in a pattern that is periodic in three
dimensions
Crystal
Single crystal Poly crystal
Types
The crystal in which
periodicity of atoms or
molecules extends
throughout the
materials is called
single crystal
The crystal in which
periodicity of atoms or
molecules does not
extend throughout the
materials but
interrupted by grain
boundary is called
poly crystal
Diamond, Quartz, Salt
Example

4. Portfolio Presentation
Unit cell
The smallest repeating unit of the crystal lattice
is the unit cell, the building block of a crystal.
Simple
cubic
When metal atoms are arranged with spheres
in one layer directly above or below
spheres in another layer, the lattice
structure is called simple cubic
• they only “fill” about 52% of the volume of the container
• simple cubic array, the coordination number is, therefore, six
• In a simple cubic lattice, the unit cell that repeats in all directions is a
cube defined by the centers of eight atoms
• there is 1 atom within one simple cubic unit cell

5. Body Centered Cubic
Some metals crystallize in an arrangement that has a
cubic unit cell with atoms at all of the corners and an
atom in the center, as shown in Figure. This is called
a body-centered cubic (BCC) solid.
Simple cubic
• Atoms in the corners of a BCC unit cell do not contact each other but contact the atom
in the center.
• an atom in a BCC structure has a coordination number of eight
• Atoms in BCC arrangements are much more efficiently packed than in a simple cubic
structure, occupying about 68% of the total volume
• Isomorphous metals with a BCC structure include K, Ba, Cr, Mo, W, and Fe at room
temperature
Face Centered Cubic
A face-centered cubic solid has atoms at the corners and, as the
name implies, at the centers of the faces of its unit cells.
• Atoms in an FCC arrangement are packed as closely together as possible occupying 74%
of the volume
• In FCP, there are three repeating layers of hexagonally arranged atoms. Each atom
contacts six atoms in its own layer, three in the layer above, and three in the layer
below.

6. Atoms of different
Size
When two or more different sizes of atoms are mixed together in a solid, two factors must be
considered:
(1) the type of site and
(2) the number of sites occupied
In the above figure a,b the interstitial atoms touch the larger atoms, and hence
they are stable; but they are not stable in c. At some critical value the
interstitial atom will fit the space between six atoms (only four atoms are
shown in two dimensions), which will yield the maximum interaction between atoms
and consequently the most stable structure results. Thus, at a certain radius
ratio of the host and interstitial atoms the arrangement will be most stable

7. IMPERFECTIONS IN CRYSTALLINE STRUCTURES
►Point Defects
►Line Defects
►Planar
Defects

8. Point Defects
01
Point defects are where an atom is missing or at an irregular place in
lattice structure
Types
Point
Defects
Intrinsic Extrinsic
Vacancy
Self
Interstitial
Substitution
impurity
atom
Interstitial
impurity
atom
A point defect can be an atom missing from a site in the crystal
(a vacancy) or an impurity atom that occupies either a normal lattice
site (a substitutional impurity) or a hole in the lattice between atoms
(an interstitial impurity).

9. Line Defects
02
Defect that is produced due to the misalignment of atoms in a crystal
lattice.
Types Line Defects
Edge
Dislocation
Screw
Dislocation
• The line defects, called dislocations, are created when an extra
plane of atoms is displaced
or dislocated out of its regular lattice space registry.
• The line defects or dislocations will lower the strength of a solid
crystal enormously since it takes much less energy to
move or deform a whole plane of atoms one atomic distance at a
time rather than all at once.

10. Planar Defects
03
In planar defect, boundaries or planes are formed, separate the
structure into regions, having the same crystal structure but different
orientation.
Types
Point
Defects
Stacking
faults
Grain Boundaries
Twin Boundaries
Planar defects exist at the grain boundaries. Grain boundaries are
created when two or
more crystals are mismatched at the boundaries. This occurs during
crystallization.
Within each grain all the atoms are in a lattice of one specific
orientation. Other grains have the same crystal lattice but different
orientations, creating a region of mismatch.
The grain boundary is less dense than the bulk, hence most diffusion of
gas or liquid takes place along the grain boundaries. Grain boundaries
can be seen by polishing and subsequent etching of a “polycrystalline”
material. This is due to the fact that the grain boundary atoms possess
higher energy

11. LONG-CHAIN MOLECULAR COMPOUNDS
(POLYMERS)
• Polymers have very long-chain molecules that are formed
by covalent bonding along the backbone chain. The long
chains are held together either by secondary bonding
forces — such as van der Waals and hydrogen bonds — or
primary covalent bonding forces through crosslinks
between chains.
• The long chains are very flexible and are easily
tangled. In addition, each chain can have side groups,
branches, and copolymeric chains or blocks that can also
interfere with the long-range ordering of chains.

12. Amorphous
• Some solids such as window glass do not have a regular crystalline structure.
Solids with such an atomic structure are called amorphous or non-crystalline
materials
• They are usually supercooled from the liquid state and thus retain a liquid-like
molecular structure. Consequently, the density is always less than that of the
crystalline state of the same material, indicating inclusion of some voids
• Amorphous materials are also more brittle and less strong than their
crystalline counterparts. It is very difficult to make metals amorphous since
the metal atoms are extremely mobile in the liquid state, and crystallization to
a solid is abrupt. However, one can make amorphous metal
• from liquid metal by cooling the melt sufficiently rapidly.
• The network structure of a solid results in a three-dimensional, amorphous
structure since the restrictions on the bonds and rigidity of subunits prevent
them from crystallizing.
• Common network structure materials are phenolformaldehyde (Bakelite®) polymer
and silica (SiO2)
• glass
The Network
Structure

13. Composite
• Composite materials are those which consist of two or more distinct parts.
The term “composite”
is usually reserved for those materials in which the distinct phases are
separated on a scale
larger than the atomic, and in which properties such as the elastic
modulus are significantly
altered in comparison with those of a homogeneous material.
• Accordingly, bone and fiberglass are viewed as composite materials, but
alloys such as brass or metals such as steel with carbide particles are not.
Although many engineering materials, including biomaterials, are not
composites,
virtually all natural biological materials are composites.

14. Thank You