Structure of Crystalline Solids

A set of flashcards summarizing key concepts, definitions, and relationships from the lecture on crystalline solids.

What factors influence the density of a material?

The density of a material depends on its crystal structure.

What is the relationship between material properties and crystal structure?

Material properties, such as brittleness in magnesium and beryllium, are directly related to their crystal structure.

What are some examples of materials that have varying properties due to their atomic structure?

Metals like magnesium and beryllium are brittle, while gold is not.

How do these properties vary with sample orientation?

Material properties can vary based on the orientation of the sample in relation to its crystal structure.

What is the significance of crystal structure in engineering?

Fracture and plasticity depend on crystal structure; for example, Ni-base superalloys are used in jet-engine turbine blades.

What are some applications related to corrosion and degradation in materials?

Stress-corrosion in implants, chemical corrosion in oil rigs, and hot corrosion in engines.

How can atomic substitutions affect material properties?

Substituting atoms into existing crystal structures can enhance toughness.

How many crystal systems are there based on unit cell geometry?

There are seven groups of crystal structures classified by their unit cell geometry.

What is the cube relationship in crystal systems?

In cubic systems, a=b=c and α=β=γ=90°.

What characterizes a tetragonal crystal system?

In tetragonal systems, a=b≠c and α=β=γ=90°.

In a hexagonal crystal system, what is unique about its crystallographic directions?

The hexagonal system employs a four-index Miller-Bravais coordinate system to accommodate equivalent directions.

How are crystallographic planes defined?

Crystallographic planes are defined by Miller indices, which are the reciprocals of the axial intercepts.

What is planar density?

Planar density is the number of atoms in a plane divided by the area of that plane.

What do the Miller indices represent?

Miller indices represent crystallographic planes in a simplified format using integers.

What is anisotropy in materials?

Anisotropy is the property of a material where physical properties vary depending on the crystallographic direction.

How do single crystals differ from polycrystals?

Single crystals show properties that vary with direction (anisotropic), while polycrystals may show isotropic properties if grains are randomly oriented.

What is polymorphism in materials?

Polymorphism (or allotropy) refers to materials that can exhibit more than one crystal structure.

Why are crystallographic directions important in material science?

Crystallographic directions are critical as they relate to atomic linear densities and influence material characteristics.