Homework Help
Homework Help
View Details
Assignment Help
Assignment Help
View Details
Online Tutoring
Online Tutoring
View Details
Home » Chemistry Homework Help » Organic Chemistsry » Non Stoichiometric Defects
Non Stoichiometric Defects
There are many compounds in which the ratio of positive and negative ions present in the compound differs from that required by ideal formula of the compound. Such compounds are called non-stoichiometric or bertholide compounds. In these compounds composition may vary over a wide range. For example, in vanadium oxide (VOx), x can be anywhere between 0.6 and 1.3. similarly FeO also exists as non-stoichiometric compound having composition Fe0.92 to Fe0.95O. In these compounds balance of positive and negative charges is maintained by having either extra electrons or extra positive charge. This results in defects in the crystal structure. The defects which disturb the stoichiometry of the compound are called non-stoichiometric defects. These defects are either due to the presence of excess metal or excess non-metal ions.

(a) Metal excess defects due to anion vacancies: a compound may have excess metal ion if a negative ion is absent from its lattice site, leaving a ‘hole’ which is occupied by electron to maintain electrical neutrally.

These types of defects are found in crystals which are likely to possess Schottky defects. Anion vacancies in alkali halides are produced by heating the alkali halides crystals in an atmosphere of alkali metal vapours. Under these conditions alkali metal atoms deposit on the surface and combine with metal ions. The electrons released during conversion of the metal atoms into ions diffuse into the crystals and occupy the sites vacated by anions.

The holes occupied by electrons are called F-centres (or color centres) and are responsible for the color of the compound and many other interesting properties. For example, the excess sodium in NaCl makes the crystal appear yellow, excess sodium in NaCl makes it violet and excess lithium ion LiCi makes it pink. Greater the number of F-centres, greater is the intensity of colour. Solids containing F-centres paramagnetic because the electrons occupying the ‘holes’ are unpaired.

(b) Metal excess defects due to interstitial cations: another way in which metal excess defect may occur is, if an extra positive ion is present in interstitial site. Electrical neutrality is maintained the presence of an electron in the interstitial site. This type of defects are exhibited in crystals which are likely to exhibit Frenkel defect, for example, when ZnO is heated, it loses oxygen reversibly. The excess metal is accommodated in interstitial with electrons tapped in the neighbourhood. The yellow and the electrical conductivity of the non stoichiometric ZnO are due to these trapped electrons.

(c) Metal deficiency due to cation vacancies:
the non-stoichiometric compounds may have metal deficiency due to the absence of a metal ion in the lattice site. The charge is balanced by an adjacent ion having higher positive charge. These types of defects are generally shown by compounds of transit metals. For example, non-stoichiometric cuprous oxide (Cu2O) can be prepared in laboratory.  In this oxide copper to oxygen ratio is slightly less than 2:1. This is due to the reason that some of the positions which were to be occupied by Cu+ ion are vacant whereas some positions are occupied by Cu2+ ions. Another example of this type is non-stoichiometric FeO which is mostly with a composition Fe0.95O. in the crystals of FeO some Fe2+ ions are missing and the loss of positive charged balanced by the presence of required number of ions.

Services:- Non Stoichiometric Defects Homework | Non Stoichiometric Defects Homework Help | Non Stoichiometric Defects Homework Help Services | Live Non Stoichiometric Defects Homework Help | Non Stoichiometric Defects Homework Tutors | Online Non Stoichiometric Defects Homework Help | Non Stoichiometric Defects Tutors | Online Non Stoichiometric Defects Tutors | Non Stoichiometric Defects Homework Services | Non Stoichiometric Defects

Submit Your Query ???
Topics
Activation Energy Average Rate Determination Rate Equation Value Reactions Collision Theory Reactions Temperature Effect Half Life Of Reaction Integrated Rate Equation Rate Equation Expression Reaction Mechanism Pseudo First Order Reaction Rate Equation Law Chemical Reaction Rate Additional Compounds Co-ordination Compounds Coordination Compounds Bonding Coordination Compounds Colors Octahedral Complex Splitting Tetrahedral Complex Splitting Stabilization Energy Crystal Field Theory Stability Affecting Factors Isomerism In Compounds Magnetic Properties Metal Carbonyls D-orbitals Orientation Mononuclear Compounds Naming Coordination Compounds Stability Terminology Compounds Werner Theory First Row Transition Elements Elements Electric Configuration F-block Elements Halides And Sulphides Metals-Oxides, Oxoanions Potassium Dichromate Potassium Permanganate The Actinoids The Lanthanoids Cell Potential Concentration Cells Electrolytic Solution Conductance Corrosion Gibbs Energy Electrochemical Series Rusting Electrochemical Theory Electrode Potential Electrolytic Cells Fuel Cells Galvanic Cells Electrode Potential Measurement Nerst Equation Corrosion Prevention Primary Cells Redox Reactions Salt Bridge Secondary Cells Standard Hydrogen Electrode Electrodes Types Steel Production Process Metals Extraction Metallurgy Principles Conduction In Insulators Conduction In Metals Density Of Unit Cell Solids-Electrical Properties Solids-Magnetic Properties Non Stoichiometric Defects Stoichiometric Defects Azeotropes Solutions-Colligative Properties Degree Of Association Degree Of Dissociation Depression In Freezing Point Elevation In Boiling Point Henry Law Constant Ideal Solutions Isotonic, Hypotonic Solutions Osmotic Pressure-Molar Mass Non Ideal Solutions Osmosis Solid In Liquid Solution Vapour Pressure Lowering Solubility Of Gases Solids In Liquids Solubility Types Of Solutions Liquid Solutions Pressure Adsorption Adsorption-Gases On Solids Adsorption From Solution Adsorption Applications Catalysis Chemical Adsorption Colloidal Solutions Coagulation Colloidal State Adsorption, Absorption Difference Emulsions Enzyme Catalysis Gels Heterogeneous Catalysis Homogeneous Catalysis Physical Adsorption Colloidal Solution Purification Group 15 Elements Group 16 Elements Dioxygen Chemical Reactions Dinitrogen Dioxygen The Oxygen Family Halides And Oxides Hydrogen Chloride Interhalogen Compounds Halogens Oxoacids Phosphorus Trichloride Nitric Acid Properties The Noble Gases Alcohols And Phenols C-O Bond Cleavage Phenol Preparation Ethers Alcohols General Preparation Alcohols Industrial Preparation Nomenclature Alcohols Physical Properties Phenols Preparation Phenolic Group Reactions Alkyl Group Reactions Some Commercial Alcohols Chemicals In Food Cleansing Action Of Soaps Drug Target Interaction Drugs And Medicines Non-Soapy Detergents Soaps Types Of Drugs Haloalkanes Chemical Properties Halides, Aryl Halides Haloalkanes And Halorenes Nucleophilic Substitution Halides Nomenclature Haloalkanes Physical Properties Haloarenes Physical Properties Polyhalogen Compounds Haloalkanes From Alcohols Haloalkanes From Hydrocarbons Cannizzaro Reaction Carboxylic Acid Preparation Of Acids Oxidation In Aldehydes Aldehydes, Ketones Properties Carboxylic Acid Properties Aldehydes, Ketones Preparation -COOH Group Reactions -OH Group Replacement Aldehydes, Ketones Reduction Carbonyl Oxygen Atom Commercial Carbonyl Compounds Commercial Carboxylic Acids Amines Amines Character Amines Chemical Properties Cyanides, Isocyanides Diazonium Salts Amines Types Aliphatic Amines Nomenclature Ortho Effect Amines Physical Properties Preparation Of Amines Diazonium Salts Properties Amines With Nitrous Acid Amines With Aldehydes Amines-Structure Basicity Biodegradable Polymers Polymerization Mode Polymers-Molecular Forces Polymers-Molecular Mass Natural, Synthetic Polymers Natural Rubber Polymers Condensation Polymers Polydienes Preparation Polyhallolefins Preparation Structure Based Polymers Synthetic Rubber