Question

In crystallography, what is the significance of Miller indices?

• A. They denote the temperature at which a material melts
• B. They describe the directions and planes in a crystal lattice
• C. They indicate the molecular weight of the crystal
• D. They determine the electrical conductivity of the material

Hint:

Remember: Miller indices = (h k l) = directions/planes in crystals. They are like coordinates that help describe geometry inside a crystal.

Answer 1

The Correct Option is B

Miller indices are a notation system in crystallography that describes the orientation of crystal planes and directions within a crystal lattice.
Understanding the Concept:

• Crystals are made of repeating patterns called lattices. These lattices have specific planes (flat surfaces) and directions which are important for understanding the crystal structure.
• Miller indices are written as sets of three integers (h, k, l), like (1 0 0) or (1 1 1), and they represent planes in the crystal.
• These indices are derived by taking the reciprocal of the intercepts the plane makes with the crystal axes and then clearing fractions.
• They help in analyzing diffraction patterns, determining crystal structure, and studying material properties like slip planes (important in deformation and strength studies).

Why Other Options Are Incorrect:

• (A) Melting temperature is a thermal property, unrelated to Miller indices.
• (C) Molecular weight depends on the chemical composition, not on crystal plane orientation.
• (D) Electrical conductivity depends on material structure and bonding, but not directly on Miller indices.

Hence, the correct use of Miller indices is to describe directions and planes in a crystal lattice.