What is the number of spheres in hexagonal close-packed crystal structure?

Answer 1

The hexagonal structure of alternating layers is shifted so its atoms are aligned to the gaps of the preceding layer. The atoms from one layer nest themselves in the empty space between the atoms of the adjacent layer just like in the fcc structure. However, instead of being a cubic structure, the pattern is hexagonal.

The hcp structure has three layers of atoms. In each the top and bottom layer, there are six atoms that arrange themselves in the shape of a hexagon and a seventh atom that sits in the middle of the hexagon. The middle layer has three atoms nestle in the triangular "grooves" of the top and bottom plane. Note that there are six of these "grooves" surrounding each atom in the hexagonal plane, but only three of them can be filled by atoms.

SAMPLE:

· Nickel Arsenide Structure s based on a distorted hcp array of Arsenide anions. By contrast with the wurtzite structure, however, which is also of formula AB, the cations now occupy all the octahedral sites rather than half the tetrahedral holes. There is one octahedral hole for each hcp lattice site, and so the AB stoichiometry is preserved.· Titanium Oxide, TiO2. he anions occupy the hcp lattice, and the cations occupy half of the octahedral holes.

• Lutetium
• Thallium
• Terbium

Answer 2

at midplane: 3 atoms
at the corners: 1/12*12=1 atom
at the center face atoms: 2 atoms
total=6 atoms in hexa.

Answer 3

Mostly 3 spheres