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MSE Ch 3

Atomic and Ionic Arrangements

What are the 3 types of atomic or ionic arrangements? no order, short-range order (SRO), long-range order (LRO),
___ display no order. Monatomic gases
Steam would be an example of ___ order. short-range
A material displays SRO if ___. the special arrangement of atoms extends only to the nearest atoms.
A material displays LRO if ___. the special arrangement of atoms extends over 100 nm.
___ order materials form a regular repetitive, grid-like pattern in 3 dimensions. We refer to them as ___ materials. Lon-range, crystalline
Single crystal materials consist of ___. one large crystal
An example of a single crystal is ___. silicon used for computer chips
A ___ material is comprised of many small crystals with varying orientations in space. polycrystalline
Borders between crystals of polycrystalline materials are called ___. grain boundaries
Many properties of polycrystalline materials depends on ___. physical and chemical characteristics of grains and grain boundaries
Many properties of single crystal materials depends on ___. chemical composition and specific direction within the crystal called crystallographic directions
___ are polymorphic materials that behave as amorphous materials in one state with regions of crystal when some outside force like electricity is provided. Liquid crystals
What are the 4 types classifications of materials based on type of atomic order? monatomic gases, amorphous materials, liquid crystals, crystalline materials
T or F? Liquid crystals can exhibit both short and long range order. True
Most materials want to naturally form periodic arrangements since this configuration maximizes the ___ of the material. thermodynamic stability
Glasses are crystalline structures that are ___ and plastics are ___. (organic/inorganic) inorganic, organic
The result of nucleating ultrafine crystals into amorphous glasses is ___. glass-ceramics
Some glass-ceramics can be made optically transparent by ___. keeping the size of crystals very small (~<100 nm)
T or F? Plastics naturally have polymers that are disorganized and tangled. True
When adding forces to plastics such as blow-stretch forming, some polymer chains are untangled causing ___. stress-induced crystallization
T or F? Metals tend to form crystalline materials rather easily. True
To prevent crystallization of metals and instead form metallic glasses, metals must be ___ very quickly at a rate of ___ in a process called ___. quenched, >10^6°C/s, rapid solidification
The natural tendency for amorphous materials is to ___. crystallize
A lattice is a collection of points called ___, which are arranged in a periodic pattern so that the surrounding of each point in the lattice are ___. lattice points, identical
A lattice may be one, two, or three ___. dimensional
A group of one or more atoms, located in a particular way with respect to each other and associated with each lattice point, is known as the ___ or ___. motif, basis
___ = lattice + basis. Crystal structure
The ___ is the subdivision of a lattice that still retains the overall characteristics of the entire lattice. unit cell
There are ___ unique arrangements of lattices known as ___. 7, crystal systems
The 7 crystal systems are ___. cubic, tetragonal, orthorhombic, hexagonal, rhombohedral (trigonal), monoclinic, triclinic
Among the 7 crystal systems there are ___ arrangements known as ___. 14, Bravais lattices
There are ___ cubic lattices, ___. 3, simple cubic (SC), face-centered cubic (FCC), body-centered cubic (BCC)
There are ___ tetragonal lattices, ___. 2, simple, body-centered
There are only one of ___, ___, and ___ lattices. hexagonal, rhombohedral (trigonal), triclinic
There are ___ orthorhombic lattices, ___. 4, simple, body-centered, base-centered, face-centered
There are ___ monoclinic lattices, ___. 2, simple, base-centered
___, which describe the size and shape of the unit cell, include the dimension of the sides and the angles. Lattice parameters
1 nm = ___ cm. 10^-7
1 nm = ___ angstroms. 10
1 angstrom = ___ cm. 10^-8
A lattice point at a corner of one unit cell is shared by ___ adjacent unit cells and thus has only ___ in each cell. So for a SC cell each one would have total of ___. 7, 1/8, 1
In most metals, ___ atoms/s is/are located at each point. one
Each BCC cell contains ___ total atom/s. 2
Each FCC cell contains ___ total atom/s. 4
Directions in a unit cell where atoms are in continuous contact are called ___ directions. close-packed
For SC cells, a = ___, where r = atomic radius. 2r
For BCC cells, a = ___. 4r/√3
For FCC cells, a = ___. 4r/√2
In BCC the <111> direction is the equation ___. (√3)a
In FCC the <011> direction is the equation ___. (√2)a
In BCC 4r = ___. a√3
In FCC 4r = ___. a√2
The ___ is the number of atoms touching a particular atom, or the number of nearest neighbors of that atom. coordination number
For ionic solids, the coordination number of cations is defined as the number of nearest ___ and vice versa. anions
The coordination number for SC is ___. 6
The coordination number for BCC is ___. 8
The coordination number for FCC is ___. 12
The packing factor is the ___. space occupied by atoms in a unit cell
Packing factor = ___. ((# of atoms in a cell)(volume of each atom))/(volume of the cell)
Volume of a sphere is calculated by ___. (4πr³)/3 or (4/3)πr³
For FCC, PF = ___. (4*(4/3)πr³)/a³ (which equals .74)
A ___ structure is the highest possible PF. close-packed
FCC cells have a PF of ___, BCC is ___, and SC is ___. Which is close-packed? .74, .68, .52, FCC
T or F? Hexagonal and FCC can have the same PF. True
Metals have a close-packed arrangement if ___. only metallic bonds are present
Density = ___. (using properties of crystal structure) ((# of atoms per cell)(atomic mass))/((Vol. of cell)(6.02x10^23))
In hexagonal close-packed (HCP) a = ___ and c = ___. 2r, 1.633a
The maximum packing factor you can get is π/√18. This is known as ___. Kepler's conjecture
In metals with an ideal HCP structure, the a and c axes are related by the ratio ___. c/a = 1.633
Materials that can have more than one crystal structure are called ___ or ___. allotropic, polymorphic
The term allotropy is normally reserved for ___. pure elements
The term polymorphism is normally reserved for ___. compounds
T or F? As temperature increases more symmetric crystal structures become less stable. False. They become MORE stable.
Adding dopants such as ___ stabilize the cubic phase of zirconia. yttria (Y_2O_3)
Specific volume is the inverse of ___. The formula is ___. density, sV = 1/D
The volume of a tetragonal cell is given by the formula ___. v = a²c
The percent change in volume is given by the formula ___. (final volume - initial volume)/(initial volume) * 100
Directions in a unit cell are described by ___. Miller indices
To determine the index for a direction subtract the ___ from the ___. tail, head
Indices for directions are enclosed in ___. The is called ___ form. [], vector
Negative number in Miller indices are noted with ___. a bar above them
Directions that are ___, are identical. parallel
T or F? [100] = [-100] (NOTE: using (-) is non-standard) False. They go in opposite directions.
T or F? [100] = [200] True. They are parallel so they are identical.
[100] is ___ to [010]. equivalent
[100] is ___ to [200]. identical
Groups of equivalent directions are known as ___ and are enclosed in ___. directions of a form, ‹›
[110], [011], and [101] are all directions of the form ___. ‹110› (NOTE: there are 12 total)
Directions of a form are made by ___. redefining the coordinate system
___ is the distance between lattice points along a direction. Repeat distance
___ is the number of lattice points per unit length along a direction. Linear density
Linear density is the reciprocal of the ___. repeat distance
Linear ___ is the fraction covered by atoms. packing fraction
What are the steps of determining a direction? 1. determine 2 points on the direction. (If a plane passes through the origin the origin MUST BE MOVED) 2. subtract the tail from the head. 3. clear fractions and reduce to lowest integers if needed.
When writing Miller indices of planes we enclose them in ___. ()
Planes of a form are enclosed in ___. {}
What are the steps of determining a plane? 1. identify points where they intercept axes. 2. take the reciprocals of the intercepts. 3. clear fractions, but DO NOT reduce to lowest integers.
(020) and (0-20) are ___. (NOTE: using (-) is non-standard) identical
T or F? (100) is equivalent to (200). False, Planes and their multiples are not identical.
Planar density is ___. the number of atoms per unit area whose CENTERS lie on the plane
Planar packing fraction is ___. the fraction of the area of a plane that is covered by atoms
Planar D = ___. # of atoms/area of the plane
Planar PF = ___. area of atoms on the plane/area of the plane
Area of an equilateral triangle is given by the formula ___. A = (√3/4)s², where s = the length of a side
Area of a circle is ___. πr²
What is the coordination number for an HCP point? 12
What is the coordination number for an FCC point? 12
What is the stacking sequence of FCC? ABCABC
What is the stacking sequence of HCP? ABABAB
What are the spaces called among cells? interstitial sites
Cubic interstitial sites have a coordination number of ___. 8
Tetrahedral interstitial sites have a coordination number of ___. 4
Octahedral interstitial sites have a coordination number of ___. 6
T or F? Atoms that are slightly smaller than the interstitial site fill the site. False. They are slightly larger and "squeeze" into the site. Smaller atoms are not allowed.
In ionic materials such as ceramics, ___ form the Miller-Bravais structure and ___ fill the interstitial sites. anions, cations
The ratio of the sizes of ionic radii of anions and cations is the ___ and is abbreviated ___. radius ratio, r/R
As a general rule, __ions are larger than __ions. an-, cat-
The coordination of ions is the number of ___. oppositely charged ions
What is the range of r/R for a linear interstitial site? 0-0.155
What is the range of r/R for a center of triangle interstitial site? 0.155-0.225
What is the range of r/R for a center of tetrahedron interstitial site? 0.225-0.414
What is the range of r/R for a center of octahedron interstitial site? 0.414-0.732
What is the range of r/R for a center of cube interstitial site? 0.732-1
What structure is CsCl? SC, but the cube is formed by the cation
What structure is NaCl? FCC
What structure is ZnS (zinc blende)? FCC, but only half of the interstitial sites are filled with S-²
What structure is CaF_2 (fluorite)? FCC, with all interstitial sites filled
Created by: drjolley
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