p.5
Polymorphism and Polytypism
What are the two polytypes of SiC?
Wurtzite and zinc blende.
p.11
Polymorphism and Polytypism
What are the lattice parameters for Wurtzite structure?
a = 0.3076 nm, c = 0.5048 nm.
What projections should be drawn for hematite?
[0001], [11 ¯00], and [112 ¯0].
What projections should be drawn for ZnO?
[0001], [11 ¯00], and [112 ¯0].
What is the task related to UO2 in the exercises?
Estimate the radius of the cubic interstice and discuss using Pauling’s rules.
What is the relationship that needs to be explained for FeS2?
The relationship between its crystal class and space group.
How does the ionic radius ratio affect the coordination number in CsCl?
The ratio of ionic radii (r Cs+ / r Cl-) is 0.94, which is greater than 0.732, indicating 8-fold coordination.
p.2
Applications of Ceramic Materials
What types of materials adopt the CsCl structure?
The CsCl structure is adopted by some important intermetallics like NiAl and halides such as CsBr, CsI, TlCl, and TlBr.
Who won the Nobel Prize in Physics in 1915 for their work in crystal structure analysis?
W.H. Bragg and W.L. Bragg.
p.12
Applications of Ceramic Materials
What significant achievement is Ferdinand Frédéric-Henri Moissan known for?
Synthesizing silicon carbide, later named moissanite.
What does IUCr stand for?
International Union of Crystallography.
Why is understanding linking, distorting, and substituting polyhedra important?
It helps in comprehending the structures of ceramic materials.
What is the coordination number for Cs+ in the CsCl structure?
The coordination number is 8.
What is the significance of the 1-2 coordination in UO2?
It can accommodate nuclear fission products without straining the lattice.
p.5
Cubic Crystal Structures
What type of bonding is primarily found in SiC?
Covalent bonding (approximately 88%).
p.7
Properties of Transition Metal Oxides
What are the two main oxides of copper?
Cu2O (cuprite) and CuO (tenorite).
p.11
Polymorphism and Polytypism
What is the lattice parameter for Zinc blende?
a = 0.308 nm, c = 0.755 nm.
What is the significance of Pauling’s rules in the context of these structures?
They were developed for ionic materials and may be compromised by covalent components.
p.11
Applications of Ceramic Materials
What is an application of CaF2?
Used in UV lithography as 200-mm-diameter crystals.
p.7
Properties of Transition Metal Oxides
What type of semiconductor is Cu2O?
A p-type semiconductor due to excess oxygen atoms.
p.10
Polymorphism and Polytypism
What is polytypism in the context of crystal structures?
Polytypism is a one-dimensional type of polymorphism where different crystal structures differ only in the stacking order of two-dimensional layers.
p.10
Polymorphism and Polytypism
What notation is used to describe the stacking sequence in polytypic forms?
The Ramsdell notation is used, consisting of a number (indicating the number of layers) and a letter (indicating the structure type).
Why are certain oxides like FeS2, TiO2, CuO, and Cu2O included in the discussion?
They illustrate special features found in oxides.
p.1
Cubic Crystal Structures
What is the lattice type of CsCl?
Simple cubic (sc) lattice with a two-atom basis.
What is the coordination number for ions in the NaCl structure?
The coordination number is 6 for both anions and cations.
What is essential to understand ceramic materials?
Their basic crystal structures.
p.4
Binary Crystal Structures
How is the structure of certain binary compounds formed?
By stacking anions in an fcc sequence and filling half the tetrahedral interstices with cations.
p.6
Binary Crystal Structures
Describe the structure of pyrite (FeS2).
Fe cations sit inside a sulfur octahedron with no edge sharing.
p.5
Applications of Ceramic Materials
What is GaN primarily used for?
Manufacturing blue-green laser diodes and LEDs.
What is the mineral CaF2 commonly known as?
Fluorite, fluorspar, and Blue John.
What is the structure of CuO?
Monoclinic with the 2/m crystal class.
p.10
Polymorphism and Polytypism
What is the Ramsdell symbol for carborundum III?
The Ramsdell symbol is 4H, indicating a hexagonal structure with a sequence of four layers that repeats.
p.2
Binary Crystal Structures
How is the NaCl structure represented?
It can be represented as two interpenetrating face-centered cubic (fcc) lattices: one of anions and one of cations.
What are the Néel temperatures for MnO, FeO, and CoO?
122 K for MnO, 198 K for FeO, and 293 K for CoO.
What is the relationship between the ionic radii of Mg2+ and O2- in MgO?
The ratio r Mg2+/r O2- is 0.6, indicating that Mg must be surrounded by oxygen ions in an octahedral configuration.
What is an example of isomorphous materials mentioned in the text?
InP, InSb, GaP, and cubic SiC.
p.10
Binary Crystal Structures
What is the crystal structure of graphite?
Graphite has a hexagonal crystal structure with lattice parameters a = 0.2456 nm and c = 0.6696 nm.
How is the coordination number determined in transition metal carbides and nitrides?
By the radius ratio of the interstitial atom to the metal atom.
p.10
Binary Crystal Structures
What properties of graphite are influenced by the long bond distance in the c-direction?
Graphite exhibits similar properties to a solid lubricant due to weak bonds between pairs of basal planes.
What is the APF for GaAs and what are the atomic radii for Ga and As?
APF is 0.41; atomic radii are 0.135 nm for Ga and 0.125 nm for As.
What should be investigated regarding rutile in the exercises?
Whether rutile obeys Pauling’s rules.
What is the significance of polyhedra in crystal structures?
They help in understanding the filling of space by ions in a lattice.
p.9
Applications of Ceramic Materials
What are some applications of single-crystal sapphire?
Used in watch bearings and pressure-resistant windows.
What happens to NiO below its Néel temperature?
It exhibits magnetic ordering and becomes rhombohedral.
What is the significance of the octahedral interstice in NaCl?
The octahedral interstice between Cl- ions must be larger than the minimum for the structure to be stable.
p.3
Properties of Transition Metal Oxides
What happens to NiO when heated in air?
It oxidizes and becomes a semiconductor.
p.6
Binary Crystal Structures
How does the structure of pyrite compare to NaCl?
Both have an fcc cell, but pyrite has lower symmetry.
p.4
Polymorphism and Polytypism
How is the wurtzite structure formed?
By arranging anions with hcp stacking and filling half the tetrahedral interstices with cations.
p.10
Binary Crystal Structures
How do the properties of graphite differ within and perpendicular to the sheets?
Within the sheets, graphite has metallic properties, while perpendicular to the sheets, it behaves more like a semiconductor.
What is the bond strength calculation for BeO?
S Be2+ = +2 - 4 = +1 - 2.
p.7
Polymorphism and Polytypism
What trend is observed in the symmetry of TiO2 structures?
Rutile has the highest symmetry, followed by anatase, then brookite with decreasing symmetry.
Which polyhedra are important in the study of ceramic materials?
Tetrahedron and octahedron.
p.12
Binary Crystal Structures
Name some binary compounds that are important to know.
CsCl, NaCl, GaAs, AlN, CaF2, MoS2, Al2O3.
p.5
Applications of Ceramic Materials
What is the primary use of BeO and AlN?
Electronic packaging due to their high thermal conductivity.
What crystal group does Cu2O belong to?
Cubic with the m3m crystal group.
How is the structure of Cu2O visualized?
By replacing Si atoms in the Si structure with O2− anions and placing Cu+ cations between them.
What is the coordination of Cu ions in the Cu2O structure?
Four Cu ions form an fcc unit cell with two O ions occupying tetrahedral sites.
What do Pauling's rules say about sharing faces of polyhedra?
It is not favorable to share faces of polyhedra.
What is unusual about the coordination number for silver and copper ions in Ag2O and Cu2O?
The coordination number is four, which is unusual for these ions.
What common structure do NaCl, TiC, and PbS share?
They all have the same structure.
p.3
Properties of Transition Metal Oxides
What is the significance of nonstoichiometric oxides like FeO?
They exist in a range of compositions due to vacancies, leading to two valence states.
p.10
Binary Crystal Structures
What is the bond length of C–C in graphite sheets?
The C–C bond length in the sheets is 0.142 nm.
p.4
Polymorphism and Polytypism
What is the structure of AlN compared to GaAs?
AlN has one [0001] direction while GaAs has four identical <111> directions.
p.6
Binary Crystal Structures
What types of compounds share a structure with FeS2?
Many binary metal chalcogenides and a few oxides.
p.10
Polymorphism and Polytypism
What are allotropes? Give an example.
Allotropes are different solid phases of the same element; for example, graphite and diamond are allotropes of carbon.
What is the significance of the structures of NaCl, TiC, and PbS in relation to Pauling’s rules?
They are examples of Pauling’s rules in action.
p.9
Applications of Ceramic Materials
What is the main use of hot-pressed powders of aluminum oxide?
As electrical insulators, windows or radomes transparent to microwaves.
p.9
Properties of Transition Metal Oxides
What is the significance of MoS2 as a material?
It is an excellent dry lubricant.
p.9
Binary Crystal Structures
How are the Mo atoms positioned in the structure of molybdenite?
In the positions corresponding to the unit cell of the hcp structure.
p.11
Properties of Transition Metal Oxides
Why must the orientation of crystals be controlled in optical applications?
Because the optical properties depend on the crystal orientation.
What is the stacking sequence for wurtzite and zinc blende structures?
Wurtzite: ABABAB; Zinc blende: ABCABC.
p.13
Properties of Transition Metal Oxides
What comparison needs to be made regarding high cristobalite and silica glass?
The densities of high cristobalite and silica glass.
What is the relationship between crystal structures and symmetry?
Other crystal structures can be related to those discussed with small distortions.
p.2
Binary Crystal Structures
What is the structure of CsCl?
The CsCl structure consists of two interpenetrating simple cubic (sc) lattices, one of Cs+ and one of Cl-.
p.6
Applications of Ceramic Materials
Why is CaF2 important for semiconductor lithography?
It is transparent at shorter wavelengths of deep-UV light.
p.8
Binary Crystal Structures
What is the relationship between hematite (Fe2O3) and alumina (Al2O3)?
Hematite is isomorphous with alumina.
p.8
Binary Crystal Structures
What structural feature distinguishes the corundum structure?
The Al3+ ions occupy two-thirds of the octahedral interstices.
p.8
Binary Crystal Structures
How many parallel (0001) planes of oxygen ions are required to build the Al2O3 rhombohedral cell?
Six parallel (0001) planes.
p.5
Cubic Crystal Structures
What type of packing do S2− ions have in wurtzite and zinc blende structures?
hcp packing for wurtzite and fcc packing for zinc blende.
How do the polyhedra in simple structures relate to more complex structures?
They reappear in much more complex structures.
How are octahedra arranged in the rutile structure of TiO2?
Linked together with one rotated octahedron in the center of the unit cell.
p.4
Binary Crystal Structures
What is the significance of the <110> directions in binary compounds?
There are six equivalent <110> directions, which optimize detail in high-resolution TEM images.
p.8
Binary Crystal Structures
What is the crystal structure of Al2O3?
Trigonal with a 3¯m crystal class.
p.9
Binary Crystal Structures
What type of structure do MoS2 and CdI2 have?
hcp (hexagonal close-packed) structure.
p.4
Properties of Transition Metal Oxides
What property do materials with a GaAs structure usually have?
They are usually semiconductors due to covalent bonding.
p.3
Cubic Crystal Structures
What is the classical name for the structure of ZnS?
Zinc blende or sphalerite.
What unique feature does the Cu2+ ion exhibit in CuO?
Square-plane coordination.
p.10
Polymorphism and Polytypism
What happens to quartz at pressures around 2 GPa?
Quartz transforms into coesite.
What does the chapter suggest about the growing importance of nonoxide ceramics?
Assumptions about cation and anion sizes may no longer be valid.
p.11
Properties of Transition Metal Oxides
What is the best crystal orientation for large sapphire windows?
Cut from (0001) crystals.
p.10
Polymorphism and Polytypism
How many polytypes of silicon carbide (SiC) have been determined?
More than 200 SiC polytypes have been determined.
p.7
Properties of Transition Metal Oxides
What are some other oxides that share the rutile structure?
CrO2 (ferromagnetic), VO2, and MnO2 (antiferromagnetic).
p.7
Polymorphism and Polytypism
What are the three structures of TiO2?
Rutile, anatase, and brookite.
What is the focus of the chapter on binary compounds?
Describing important simple (binary) crystal structures found in ceramic materials.
How are traditional ceramic oxides typically structured?
As a three-dimensional array of anions with cations in the interstices.
p.1
Cubic Crystal Structures
What types of lattices are mentioned as particularly simple cases?
Simple-cubic (sc), hexagonal close-packed (hcp), and face-centered cubic (fcc).
What is a potential issue when applying Pauling’s rules?
They may not apply accurately in compounds with significant covalent bonding.
