Point defects of solids

In a crystalhne sohd the point lattices are normally occupied by atoms, molecules or iorts called components. The lattice thus formed is called the perfect lattice. In practice, this lattice can display irregttlarities that are called defects. 

A point defect is an irregularity at the level of a point lattice and the following can be encountered  

A stractural element is an atom, ion or vacancy (empty space) at a specific site of the crystal. The notion of stmctural element combines the notions of a chemical species and its surroundings through the nature of the lattice site being considered. A stmctural element can be  

We can thus completely describe the solid from the enumeration of its stmctuie elements by assimilating free electrons and electron holes that might be present in order to be complete. 

Stmcmre elements can cany variable charges. The effective charge of a stmcmral element, qe, is the difference between its actual charge (qr) and the charge that the structural element occupying the same site in the ideal crystal would have (the normal charge, qn)  

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The changes in non-stoichiometry and point defects of solid perovskite (BaTiOs) at 900°C can be observed with Raman spectroscopy (51). The method is believed to be more sensitive than the neutron scattering technique and has become the standard in determining stoichiometric information for solid materials. The interest in perovskite-type materials stems from their use in solid-state capacitors. 

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