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Crystal lattice defects are disruptions in the orderly pattern of a crystal's structure. In an ideal crystal, atoms or ions are arranged in a repeating pattern, extending in all three spatial dimensions. However, in reality, no crystal is perfect; defects invariably occur and these imperfections can significantly affect the physical and chemical properties of the material, including electrical conductivity, optical clarity, and mechanical strength.

There are several types of defects that can occur within a crystal structure. These include point defects, which involve a single or a small cluster of atoms; line defects, which pertain to discrepancies along a line in the crystal; and planar defects, which occur across a two-dimensional plane within the crystal. These imperfections are not mere anomalies but can be integral to the functionality of materials in various applications, such as semiconductors and ceramics.

In the context of point defects, the Schottky defect is a vacancy defect occurring in compound crystals, such as ionic crystals. This defect involves equal numbers of cations and anions leaving their lattice sites, thereby maintaining electrical neutrality. The evacuated sites are known as vacancies.

The presence of Schottky defects has implications on the density and ionic conductivity of the material. Since atoms are missing from the crystal lattice, the density of the crystal decreases. These defects are predominant in compounds with high coordination numbers and where ions have similar sizes. A typical example of a material exhibiting Schottky defects is sodium chloride (NaCl), where approximately one out of every million sodium ions is missing from its lattice site.

Point defects in crystals are imperfections at the atomic or ionic scale that disrupt the ideal periodic arrangement within a crystal lattice. These can be viewed as 'mistakes' in the otherwise orderly pattern of atoms. They are categorized into different types, such as vacancies, interstitials, and substitutional atoms or ions. Each type of point defect carries distinct characteristics and results in different property alterations of the crystal.

Vacancies are points where an atom is missing, interstitials occur when atoms occupy spaces between the regular lattice sites, and substitutional defects happen when a foreign atom replaces a host lattice atom. The behavior and concentration of point defects can be influenced by factors such as temperature, with higher temperatures generally increasing the number of point defects due to increased atomic mobility. In the case of point defects, like the Frenkel defect, it involves an atom or ion vacating its lattice position to occupy an interstitial site. This can lead to increased ionic conductivity as the presence of these defects provides a pathway for ions to move through the lattice.