Solid State Flashcards
Define Crystalline solid
A solid in which the constituent particles like atoms, ions or molecules are arranged indefinite repeating patterns throughout the solid is called crystalline solid. For example, and NaCl, KNO3.
Define Amorphous solid
A substance which appears like solid but does not have perfectly ordered crystalline structure and no regular arrangement of constituent particles in structure is called amorphous solid. For example, glass, rubber, plastic, etc.
Define polymorphism.
The phenomena in which a single substance crystallizes in two or more forms under different solidification conditions is known as polymorphism and the substances said to be polymorphous.
Define isomorphism.
When two or more crystalline substances have the same crystal in structure they are said to be is more first for example NaF and Mg.
Define isotropy.
The ability of amorphous solid to exhibit identical physical properties even though measured in different directions is known as isotropy.
Define Anisotropy.
The ability of crystalline solids to change their physical properties when measured in different directions is known as anisotropy
What is a unit cell?
Unit cell: it is the smallest repeating structural unit of a crystalline solid (or crystal lattice) which when repeated in different directions produces the crystalline solid (lattice).
Explain/How are tetrahedral voids formed?
The vacant space or void among four constituent particles having tetrahedral arrangement in the crystal lattice is called tetrahedral void.
The arrangement of force spheres around the void is tetrahedral. A tetrahedral void is formed when a triangular void made by 3 coplanar spheres is in contact with fourth sphere above or below it.
Explain/ How are octahedral voids formed?
The vacant space or void at the centre of 6 spheres (or atoms) which are placed octahedrally is called octahedral void.
What are the consequences of Schottky defect?
Consequences of Schottky defect:
(1) Since the number of ions (cations and anions) decreases but volume remains unchanged, the den- sity of a substance decreases.
(2) As the number of missing cations and anions is equal, the electrical neutrality of the compound remains same.
(3) This defect arises in ionic crystals like NaCl, AgBr,KCl, etc.
How does electrical conductivity of a semiconductor change with temperature?
Why?
(1) Since the energy difference between valence band and conduction band in semiconductor is not large, the electrons from valence band can be promoted to conduction by heating.
(2) Hence electrical conductivity of a semiconductor increases with temperature.
What are conditions for the formation of Schottky defect.
i. Schottky defect is found in ionic compounds with the following characteristics:
High degree of ionic character.
High coordination number of anion
Small difference between size of cation and anion. The ratio is not far below unity. r cation /r anionb is not far below unity.
