The Solid State
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How would you account for the following:
Schottky defects lower the density of related solids.

 It is basically a vacancy defect in ionic solids. In order to maintain electrical neutrality, the number of missing cations and anions are equal.

Thus there is equal number of positive and negtive ion leave correct lattice point and go outside the lattice creating  a pair of vacancy. So there are less number of ions thannbefore whichresult in the decrease in its density.
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    Schottky defects generate an equal number of cation and anion vacancies while doping produces only cation vacancies and not anion vacancies. Why?
    Answer
    How would you account for the following:
    Frenkel defects are not found in alkali metal halides.
    Answer
    Examine the illustration of a portion of the defective crystal given below and answer the following questions:
    (i) What are these types of vacancy defects called?
    (ii) How is the density of a crystal affected by these defects?
    (iii) Name one ionic compound which can show this type of defect in the crystalline state.
    (iv) How is the stoichiometry of the compound effected?


    Answer
    Pure silicon is an insulator. Silicon doped with phosphorus is a semi-conductor. Silicon doped with gallium is also a semiconductor. What is the difference between the two doped silicon semi-conductor?
    Answer
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