What is point defects. Describe two types of point defects.

What are point defects ? Describe Schottky defects in crystals.

Structure of diamond|Defects in solid|Point defect|Line defect|Types of point defect

What is an ideal crystal ? Name the types of the defects which arise in a crystal.

An ideal crystal has the same unit cell containing the same lattice points throughout the whole of crystal. But such ideal crystals exist only at 0 K temperature. However, during the formation of crystal structure, certain defects are produced. These defects are point defects, line defects, vacancy defects, interstitial defects or impurity defects. Due to these defect, the crystals exhibit different properties. Presence of delocalised electrons make the metals conductor of electricity . Germanium and silicon are the most important commericial semiconductors. By adding impurities such as arsenic and boron, n and p - type semiconductors can be synthesised. Various combinations of n and p type semiconductors are used to make electronic components. Name the type of point defect that occurs in a crystal of zinc sulphide. Will it increase, decrease or not change the density ?

What is presbyopia ? Write two causes of this defect. Name the type of lens which can be used to correct presbyopia.

Which point defect decreases the density of crystals ?