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  2. Close-packing of equal spheres - Wikipedia

    en.wikipedia.org/wiki/Close-packing_of_equal_spheres

    Many crystal structures are based on a close-packing of a single kind of atom, or a close-packing of large ions with smaller ions filling the spaces between them. The cubic and hexagonal arrangements are very close to one another in energy, and it may be difficult to predict which form will be preferred from first principles.

  3. Hexagonal crystal family - Wikipedia

    en.wikipedia.org/wiki/Hexagonal_crystal_family

    The nickel arsenide structure consists of two interpenetrating sublattices: a primitive hexagonal nickel sublattice and a hexagonal close-packed arsenic sublattice. Each nickel atom is octahedrally coordinated to six arsenic atoms, while each arsenic atom is trigonal prismatically coordinated to six nickel atoms. [15]

  4. Atomic packing factor - Wikipedia

    en.wikipedia.org/wiki/Atomic_packing_factor

    HCP structure. For the hexagonal close-packed structure the derivation is similar. Here the unit cell (equivalent to 3 primitive unit cells) is a hexagonal prism containing six atoms (if the particles in the crystal are atoms).

  5. Periodic table (crystal structure) - Wikipedia

    en.wikipedia.org/wiki/Periodic_table_(crystal...

    In closest packing, every atom has 12 equidistant nearest neighbours, and therefore a coordination number of 12. If the close packed structures are considered as being built of layers of spheres, then the difference between hexagonal close packing and face-centred cubic is how each layer is positioned relative to others.

  6. Sphere packing - Wikipedia

    en.wikipedia.org/wiki/Sphere_packing

    Thus, beyond this point, either the host structure must expand to accommodate the interstitials (which compromises the overall density), or rearrange into a more complex crystalline compound structure. Structures are known which exceed the close packing density for radius ratios up to 0.659786. [22] [25]

  7. Slip (materials science) - Wikipedia

    en.wikipedia.org/wiki/Slip_(materials_science)

    Slip in hexagonal close packed (hcp) metals is much more limited than in bcc and fcc crystal structures. Usually, hcp crystal structures allow slip on the densely packed basal {0001} planes along the <11 2 0> directions. The activation of other slip planes depends on various parameters, e.g. the c/a ratio.

  8. Interstitial site - Wikipedia

    en.wikipedia.org/wiki/Interstitial_site

    A close packed unit cell, both face-centered cubic and hexagonal close packed, can form two different shaped holes. Looking at the three green spheres in the hexagonal packing illustration at the top of the page, they form a triangle-shaped hole. If an atom is arranged on top of this triangular hole it forms a tetrahedral interstitial hole.

  9. Hexaferrum - Wikipedia

    en.wikipedia.org/wiki/Hexaferrum

    Hexaferrum and epsilon iron (ε-Fe) are synonyms for the hexagonal close-packed (HCP) phase of iron that is stable only at extremely high pressure.. A 1964 study at the University of Rochester mixed 99.8% pure α-iron powder with sodium chloride, and pressed a 0.5-mm diameter pellet between the flat faces of two diamond anvils.