Defects and non-stoichiometryPerfect CrystalPoint DefectsExtendedDefectsGrainDislocationsIntrinsicExtrinsicBoundaries
Defects and non-stoichiometry
Defects and non-stoichiometryINTRODUCTIONDefects can also occur at isolatedatomicpositions; these are known as point defects.Ionic solids are able to conduct electricity by amechanism which is due to the presence of vacantion sites within the lattice
Defects can also occur at isolated atomic positions; these are known as point defects. Ionic solids are able to conduct electricity by a mechanism which is due to the presence of vacant ion sites within the lattice. Defects and non-stoichiometry INTRODUCTION
Defects and non-stoichiometryDEEECTSANDTHEIRCONCENTRATIONIntrinsicdefectsIntrinsic defects fall into two categoriesSchottky defects, which consist of vacancies inthe lattice and Frenkel defects where a vacancy iscreated by an atom or ion moving into aninterstitial position
Defects and non-stoichiometry DEFECTS AND THEIR CONCENTRATION Intrinsic defects Intrinsic defects fall into two categories: Schottky defects, which consist of vacancies in the lattice and Frenkel defects where a vacancy is created by an atom or ion moving into an interstitial position
Point Defect-IntrinsicSchottkyFrenkelcation vacancyanion vacancyinterstitialcationAg* → Vag+ AgNat+ CI → Vna + Vclinterstitial
Defects and non-stoichiometryDEEECTS AND THEIR CONCENTRATIONFor a 1:1 solid MX, a Schottky defect consists ofa pair of vacant sites a cation vacancy and an anionvacancy. The number of cation vacancies and anionvacancies have to be equal in order to preserveelectrical neutralityA Schottky defect for an MX,-type structure willconsist of the vacancy caused by the Me2+ iontogether with two X- anion vacancies, therebybalancing the electrical charges
Defects and non-stoichiometry DEFECTS AND THEIR CONCENTRATION For a 1:1 solid MX, a Schottky defect consists of a pair of vacant sites a cation vacancy and an anion vacancy. The number of cation vacancies and anion vacancies have to be equal in order to preserve electrical neutrality. A Schottky defect for an MX2 -type structure will consist of the vacancy caused by the Me2+ ion together with two X- anion vacancies, thereby: balancing the electrical charges