Question

The defect when an ion occupies an interstitial position in the crystal lattice is called (a) Schottky defect (b) Crystal defect (c) Frenkel defect (d) none of these

Short answer

(c) Frenkel defect.

Step-by-step solution

Identify the type of defect

The defect in question occurs when an ion occupies an interstitial position, meaning the ion is misplaced in one of the small voids or interstitial positions within a crystal lattice.

Match description with defect type

A Frenkel defect involves an ion being displaced from its original lattice site into an interstitial position, maintaining the stoichiometry of the crystal lattice system.

Associate defect with correct option

Among the given options, the Frenkel defect described matches the situation where an ion moves from its usual position to an interstitial site. Thus, the correct choice is (c) Frenkel defect.

Key concepts

Crystal lattice

In simple terms, a crystal lattice is a three-dimensional arrangement of atoms, ions, or molecules in a crystalline solid. This structure is composed of repeating patterns, which form the essential framework for the material. Think of it like a very ordered and repeating grid which holds everything in place. There are different types of crystal lattices depending on the angles and distances between particles, commonly referred to as the unit cell.
Crystal lattices are central to the physical properties of materials. These include things like melting point, density, and conductivity. This is because the specific arrangement of particles affects how the crystal interacts with heat and electricity.
Understanding crystal lattices is important in various scientific fields, ranging from materials science to chemistry. It forms the basis for understanding more complex behaviors in crystals, including defects like the Frenkel defect.

Interstitial positions

In a crystal lattice, there are spaces that are not typically occupied by ions or atoms. These small voids or gaps are known as interstitial positions. Imagine the lattice as a packed grid; interstitial positions are like the gaps or holes within this grid.
When an ion or atom occupies an interstitial position, it is tucked into one of these gaps, which is not its usual place. This can cause changes in the properties of the material, as particles are now in places they typically wouldn't be. Interstitial atoms can impede the movement of other atoms and might even change the overall volume of the crystal.
Interstitial positions play an essential role in defects such as the Frenkel defect. Here, the displaced ion temporarily occupies one of the interstitial positions, altering the perfect lattice structure and introducing an imperfection.

Ion displacement

Ion displacement refers to the process where an ion in a crystal lattice moves from its normal position. This is usually due to external factors like temperature or pressure, which give the ions energy to move. In the context of a Frenkel defect, ion displacement occurs when an ion leaves its normal lattice site and occupies an interstitial position.
Ion displacement can have significant effects on the material's properties. For instance, it can change conductivity, as ions are no longer in their typical pathways. Additionally, the crystal's density might also be altered, as positions within the lattice shift.
In the Frenkel defect, ion displacement is crucial but does not alter the overall stoichiometry of the crystal. It's more about the redistribution within the lattice rather than loss or gain of ions. Understanding ion displacement helps in predicting and explaining different material properties and behaviors.