Exercises for KJM5120 and KJM9120
Chapter 2
Your name:
Defect reactions
Note: These exercises are part of the web-based teaching of this course. It is suggested and recommended that you fill them in and submit them electronically back to the lecturer. They will be returned to you with comments for your benefit. Note:
Submitting the exercises is not mandatory and is not part of the evaluation of you during the course. The exam at the end is the only evaluation of you in this course.
The three rules of balancing defect chemical reaction equations
The third rule is special to defect chemistry and thus basically the only new stuff you learn to apply, in addition to ordinary chemistry. It typically causes some problems to many. Therefore, you need to spend some effort on it. What does it conserve?
The number of sites of each kind?
The ratio of the number of different sites?
Yes No
Yes No
The ratio of the number of different sites in a dopant compound? Yes No
The host structure? Yes No
The composition of the host material? Yes No
(Write for instance an “X” after the correct answer. More than one Yes is possible.)
Instrinsic disorders - stoichiometric compounds
Write a reaction for the formation of Schottky defects in MO
2
Write a reaction for the formation of anion Frenkel defects in MO.
Write a reaction for intrinsic electronic exitation across the bandgap.
Non-stoichiometry
(These questions restrict themselves to the simplest and most important examples of non-stoichiometry that is a minimum knowledge….)
What are the two dominating defects in a material when it is written as MO
2-y
?
Write an equation for the formation of these two defects.
Repetition from Ch. 1: Write the electroneutrality that describes that these two defects dominate.
Write the same in words (“The concentration of…is…..the concentration of……”).
1

Do the reaction and electroneutrality statement make sense together?
Back to Ch. 2:
Doping:
We are going to dope the ZrO
2-y
with Y
2
O
3
and assume that the dopant dissolves substitutionally.
Write the doping reaction so that the doping creates a charge the relevant compensating defect.
Write the doping reaction so that it instead consumes the defect of the same effective charge as the dopant.
Which of these is the “most useful” one and why?
Ternary oxides
LiNbO
3
is a perovskite with interesting optoelectronic properties. Find the valence of the two cations and then write the reaction for formation of Schottky defects in the material.
Formulate a reaction that takes into account that metal vacancies are more easily formed on the Li sites and that Li oxide is volatile.
Protons:
Try to write a reaction that describes hydration in stoichiometric LiNbO
3
(dissolution of water) by consuming an existing defect (should be easy when you have read the chapter) or creating new ones (a challenge!?).
Your own material of choice:
Problem 25 reads: “With reference to Problem 22 in Chapter 1, the material of your choice, and its full and limiting electroneutrality: Straightforward: Write a reaction for the formation of the defects you have selected to be dominating. More difficult: Write a reaction that replaces the dominant positive defect with another positive defect. Do similar with a dominant negative defect.” Try it here:
2