Crystal Structure: Properties of Materials Depend on Structure

[mecheng]

Which properties of materials depend on the crystal structure (f.c.c., b.c.c. cph etc...) of materials?

 

[jdavel]

mecheng,

How about density? :-)

 

[Astronuc]

Probably all thermophysical and mechanical properties depend to some degree (some more so than others) on crystal structure (morphology), but then each element which is solid has a preferred crystal structure.

Interatomic spacing, as well as the inherent attraction between the atoms, affects properties like thermal conductivity and strength.

Cubic structures are more isotropic due to symmetry. Crystals which are elongated in one or two of three directions exhibit anisotropies in their properties, i.e. the properties have a directional dependence.

Hexagonal close-packed metals (e.g. Zr) have a property called 'texture' which relates to the fraction of grains with a particular orientation of the basal poles, or c-axis (normal to the basal plane) in a poly-crystalline phase.

Most metals are found in a poly-crystalline as opposed to single-crystal structure. And within either configuration, some dislocations or holes in the lattice may occur. These too have important implications with respect to properties.

 

[Gokul43201]

Which properties of materials depend on the crystal structure (f.c.c., b.c.c. cph etc...) of materials?

Virtually all of them do.

Ductility is clearly related to the existence of slip planes. The FCC structure has slip planes along (111) directions, while the BCC crystal's slip planes are the (110) family. This difference is instrumental in determining the plastic flow characteristics of the material. As a result, Cu, Ag, Au (all FCC metals) are extremely ductile, while Fe, Ni (BCC) are not. Hardness is inversely related to ductility and so hardness trends follow likewise. Tensile strength and toughness are also related to crystal structure, but other factors (microstructure, heat treatment, alloying) often dominate.

 

[Gokul43201]

Also, thermodynamic, electronic and magnetic properties are related to crystal structure.

In the High Tc Cuprites, the Cu-O planes are vital to the incidence of superconductivity. In CMR manganites, the O-Mn-O bond angle affects the MR ratio. In aluminate-based long afterglow phosphors, there is a strong correlation between the lattice parameter and the wavelength of emitted light. Mobility of semiconductors, conductivity of diamond, magnetic anisotropy in transition metal-rare Earth intermetallics, etc. are all heavily dependant on the crystal structure.