The Atomic Packing Factor APF is essentially the density of the unit cell. In the face-centred cubic FCC arrangement there is one additional iron atom.įor 63 Cu the atomic mass is less than 63 so this must be the dominant factor. En cristalografía el factor de empaquetamiento atómico FEA en inglés. APF is basically the fraction of atoms to void. The packing density also known as the atomic packing factor APF is essentially the fraction of the volume of atoms that occupy a crystal structure. Hence atoms occupy 74.05% of the volume of the unit cell.Problem 1 If the atomic radius for Pb 0175nm find the volume of the unit cell. In this structure atoms touch each other along the face diagonal. EachĪtom consists of 12 equidistant nearest neighbours. In FCC structure in addition to atoms at corners, atoms are present at face centers. Hence atoms occupy 68.02% of the volume of the unit Therefore Where R is the radius of the atom There are eight atoms at corners and 1 atom at the body center, the no of atoms per unit cell is given byĪlso in this structure the atoms touch each other along the body diagonal. Hence atoms occupy 52.35% off the volume of the unit cell.Įach atom has 8 equidistant nearest neighbors. Therefore a=2R,where R is the radius of each atom In this structure the atoms touch each other along the sides of the cube. Since the atoms are present only at corners, the number of atoms per unit cell is given by Hence only 1/8th of the volume of the atom lies in each cell. Hence its co-ordination number is 6.Įight unit cells share each atom at the corner. In simple cubic structure each atom consists of 6 equidistant nearest neighbours. If the number of atoms per unit cell are n and if V a is the volume of atoms in the unit cell and V is the volume of the unit cell then,Ĭalculation of Atomic packing factor for different crystal systems It is defined as the ratio of volume occupied by atoms in unit cell to the volume of the unit cell. It is the fraction of space occupied by atoms in a unit cell. (3) Atomic packing factor (APF) or Packing fraction: It is the distance between two nearest neighbors in a crystal structure. It is the number of equidistant nearest neighbors that an atom has in a crystal structure. Coordination number and Atomic packing factor Definition
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