No crystal is found to beperfect at room temperature. The defects present in the crystals can be stoichiometric or non-stoichiometric. Due to non-stoichiometricdefects, the formula of the ionic compound is different from the ideal formula. For example, the ideal formula of ferrous oxide should be FeO but actually in one sample, it was found to be Fe_(0.93)O. This is because the crystal may have some ferric ions in place of ferrous ions. These defects change the properties of the crystals. In some cases, defects are introduced ot have crystals of desired properties as required in the field of electronics. Doping of elements of group 14 with those of group 13 or 15 is most common. In ionic compounds, usually the impurities are introduced in which the cation has higher valency than the cation of the parent crystal e.g.,SrCl_(2) into NaCl. NaCl was doped with 10^(-3) mol % SrCl_(2).The concentration of the cation vacancies is

No crystal is found to beperfect at room temperature. The defects pres

1.	No crystal is found to beperfect at room temperature. The defects present in the crystals can be stoichiometric or non-stoichiometric. Due to non-stoichiometricdefects, the formula of the ionic compound is different from the ideal formula. For example, the ideal formula of ferrous oxide should be FeO but actually in one sample, it was found to be Fe_(0.93)O. This is because the crystal may have some ferric ions in place of ferrous ions. These defects change the properties of the crystals. In some cases, defects are introduced ot have crystals of desired properties as required in the field of electronics. Doping of elements of group 14 with those of group 13 or 15 is most common. In ionic compounds, usually the impurities are introduced in which the cation has higher valency than the cation of the parent crystal e.g.,SrCl_(2) into NaCl. NaCl was doped with 10^(-3) mol % SrCl_(2).The concentration of the cation vacancies is
Answer» `6.02times10^(18)"mol"^(-1)` `6.02times10^(15)"mol"^(-1)` `6.02times10^(15)"mol"^(-1)` `6.02times10^(12)"mol"^(-1)` Solution :Doping of NACL with `10^(-3)" MOLE " SrCl_(2) " means that 100 moles of NaCl are doped with " 10^(-3) " mol of " SrCl_(2)` `therefore "1 mole of NaCl is doped with "SrCl_(2)` =`(10^(-3))/100"mole"= 10^(-5)"mole"` Since `Sr^(2+)`ion introduces one cation vacancy, therefore, concentration of cation vacancies `= 10^(-5)"mol//mol of NaCl"` =`10^(-5)times6.02times10^(23)"mol"^(-1)` =`6.02times10^(18)"mol"^(-1)`.