Crystal Structure

The correct order of the packing efficiency in different types of unit cells is _______?

• fcc < bcc < simple cubic

• fcc > bcc > simple cubic

• fcc < bcc > simple cubic

• bcc < fcc > simple cubic

Which of the following statements about lattices and unit cells is correct?

• A unit cell contains a whole number of complete molecules

• Lattice points are chosen to lie on atoms.

• Lattice points all have identical surroundings

• Unit cells are constructed by connecting adjacent lattice points to give the largest possible repeat unit.

Consider the Bragg equation. If the value of the wavelength is doubled, which of the following is NOT true?

• Bragg angles of reflections increase.

• The d spacings become smaller.

• The diffraction pattern expands.

• Some previously accessible reflections can no longer be measured.

Repeatable entity of a crystal structure is known as

• Crystal

• Lattice

• Unit cell

• Miller indices

Coordination number for BCC crystal structure is

• 16

• 12

• 8

• 4

Atomic packing factor is

• Distance between two adjacent atoms

• Projected area fraction of atoms on a plane

• Volume fraction of atoms in cell

• None

The number of Bravais lattices is:

• 256

• 7

• 14

• 37

Co-ordination no. & Atomic Packing Fraction of HCP structure is same as that of the -----------

• SC

• BCC

• FCC

• BCT

The atomic diameter of an FCC crystal is

• a

• a/2

• a/(2/√2)

• a/(4/√2)

Intercepts of a plane in crystal is given by 1, 1/2, 1/3 in a simple cubic unit cell, Miller indices are

• (1 3 2)

• (2 6 1)

• (1 2 3)

• (3 6 1)