Final answer:
Grain boundaries are a type of surface defect found in crystalline materials, where different crystalline areas meet. These boundaries display properties distinct from the interior of the grains. Understanding crystal defects like grain boundaries, point defects, and line defects is crucial for material engineering applications.
Step-by-step explanation:
The defect that grain boundaries belong to is called a surface defect. Grain boundaries form when many seeds are created during the initial crystallization of a sample, with each seed growing until they encounter each other, forming the boundaries. The properties along these grain boundaries are different from those within the grains. Another type of surface defect is the stacking fault, which occurs when layers in a crystal deviate from their usual sequence.
There are also point defects, like Frenkel and Schottky defects, which occur in ionic crystals. Frenkel defects are due to misplacement of ions and vacancies, maintaining charge balance. Schottky defects involve only vacancies without interstitials. Additionally, there are line defects, including dislocations such as edge dislocations, which are aligned along a line in the crystal lattice and are essential in understanding the malleability of materials.
Categorizing defects helps in engineering the properties of materials for specific applications, like doping silicon crystals to change electrical properties for semiconductors.