4. What point defects are possible for Al 2 O 3 as an impurity in MgO? How many

Question

4. What point defects are possible for Al2O3 as an impurity in MgO?  How many Al3+ ions must be added to form each of these defects?

One Mg2+ vacancy for every two Al3+ ions added

Three Mg2+ vacancies for every two Al3+ ions added

One O2- vacancy for every two Al3+ ions added

Three O2- interstitials for every two Al3+ ions added

One Mg2+ vacancy for every two Al3+ ions added

Three Mg2+ vacancies for every two Al3+ ions added

One O2- vacancy for every two Al3+ ions added

Three O2- interstitials for every two Al3+ ions added

Explanation / Answer

For every one Mg+2 ion,that substitutes Al+3, a single positive charge is removed. Thus inorder to maintain charge neutrality, either positive charge must be added or negative charge must be removed

By charge neutrality: Three Mg+2 vacancies for every 2 Al+3 ions

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