Shaillee Kaushal is teaching live on Unacademy Plus
XII 01 SOLID STATE IV
Parameters of a unit cell: The measurable properties of a unit cell that distinguishes it from other unit cells are called parameters of a unit cell Fig. 8. Parameters of a unit cell.
There are three angles and three edges. Angle a is in between edges b and c angle B is in between a and c angle Y is between a and b. Fig. 8. Parameters of a unit cell.
System Maximum Svmfmetty elements EXamples 1 Cubic Nine plne:s 13 axes NaCl, KCl, ZnS, diamond alums. a bc 2Tetragonal Five planes, five axis Ti02, PbWO4,Sn02, NH4Br 3Orthorhombic Three planes, three axis KnO2,Baso,, K2SO, Rhomic sulphr 4 Mononclinic One plane, one axis Monoclinic sulphur, KCIO3, CaSO4, 2H20 Hexagonal Seven planes, seven axis Zno, CdS, HgS, Sic. 120 6 Rhombohedral Seven planes seven axis NaNO3,1 Cl, quartz (CaCO3) CuSO4,5H20, K2 Cr207 7 Triclinic No planes No axis
Primitive unit cell: These are unit cells which have points only at the corners. These are called simple unit cells. atom a) Open structure bi Space iling structure (c Actual portion of atioms belongin one unit cell Pig 15. Simple cubic arrangement and number of spberes per unit cell.
2, Centred unit cell: These are unit cells which have points at the corners as well as at some other positions. The centred unit cells are of three types (i) Face centred unit cell: In these the points are present at the corners and at the centre of each face E.g Ca, Sr, Al, Co, Ni, Cu, Rn, Pd, Ag. ATOM a Open structure (b) Space lingstructure cActual portion of stoms belonging to one unit cell
Body centred unit cell: In this the points are present at all the corners as well as at the body centre of the unit cell Examples: Li, Na, K, Rb, Cs, Ba, V, Nb, Cr, MO, Fe a om t alom a Open structure b) Spae filing structure e Actual prtion of atoms belonging to one unit cell
End centred: In this the points are present at all the corners and at the centre of two opposite faces.