Crystallography Flashcards
What is Crystallography
is the science that examines the arrangement of atoms in solids. This involves measuring the angles of crystal faces relative to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question.
Crystallographic Axis
One of the imaginary reference lines passing through the center of anideal crystal, designated a, b, or c.
Polycrystalline
Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random (called random texture) or directed, possibly due to growth and processing conditions
Polymorphism and Allotropic
It’s the ability of a chemical substance to exist in more than one alternative crystal structure. It is related to allotropy and is described by crystal habit, amorphous, or crystal defect.
Polymorphism and Allotropy are same thing. Polymorphism is used for compounds and the allotropy is reserved for elements.
Crystal Twinning
A crystal structure may contain a change in repeat-direction, to form a twin. Two or more parts of a twinned crystal structure are not related by the normal symmetry of that structure. They are related by a twin reflection plane or axis, or both. The twinning of a structure may be an accident of growth, or caused by stress or change in temperature during growth.
When does Crystal Twinning occur?
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an inter-growth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws. These twin laws are specific to the crystal system. The type of twinning can be a diagnostic tool in mineral identification.
What is the Diamond Cubic Structure
The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, including α-tin, the semiconductors silicon and germanium, and silicon/germanium alloys in any proportion.
Cubic Crystal System
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex.
What is the crystallization process called?
Crystals grow by a process called “nucleation”. Nucleation can start with assisted nucleation or unassisted nucleation. It will continue to grow until an equilibrium is reached.
How fast do crystals grow?
Why crystals grow at different rates in different directions
What is the lattice system?
These lattice systems are a grouping of crystal structures according to the axial system used to describe their lattice.
How many lattice systems?
There are seven lattice systems. They are similar to but not quite the same as the seven crystal systems and the six crystal families.
What are the lattice systems?
Cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic and triclinic.
What is the lattice systems for diamonds?
Cubic
What is the cubic lattice system?
The simplest and most symmetric, the cubic (or isometric) system, has the symmetry of a cube, that is, it exhibits four threefold rotational axes oriented at 109.5° (the tetrahedral angle) with respect to each other.
