On the first day of your new job at Generally Electric, your supervisor
puts you in charge of developing a new ceramic material that will be used as part of a composite material oxygen separation membrane to be used prior to combustion of the fuel with oxygen in a gas turbine system. The material must be stable in an oxidizing (air) environment, have high electronic conductivity, and must be less expensive than the current material being used by the company.The company already has a material with excellent ionic conductivity that they will use in a composite with your new material, but they are using a composite approach in order to manage the thermal expansion coefficient and mechanical properties.
To achieve these goals, you decide to start with a very abundant, low-cost material, mundanium oxide, with chemical formula MuO2. You consult your "extended" periodic table to determine that mundanium (chemical symbol Mu) is a transition metal, i.e.,it can exist in multiple oxidation states, including one electronic charge above or one electronic charge below its normal 4+ oxidation state in ionic solids. You also know that it normally forms the non-conductive stoichiometric oxideMuO2. You hope that by adding a dopant to the mundanium oxide starting material, you can increase its conductivity.
1. You decide to try doping the material with unobtainium oxide (Un2O5) in order to increase its conductivity. You know from consulting your "extended" periodic table that unobtainium can exist only in one oxidation state in ionic solids.In order to determine whether your dopant will lead to a material with electronic or ionic conductivity, you consider the answers to the following questions:
a. What specific defects could potentially form in theMuO2, as a result of creating your solid solution by doping it with Un2O5, considering the requirements of charge neutrality? List at least two such defects.
b. defect equation using the standard Kröger-Vink notation describing the defect reaction that you hope will happen as a result of your doping of Un2O5into MuO2(i.e. a defect formation equation that would lead to increased electronic conductivity, assuming that only one of the possible defect types occurs).
c. If the defect reaction that you wrote in part (b)occurs in the material, what dependence of the conductivity on partial pressure of oxygen would you expect to see in your new solid solution material?
d. defect equation using the standard Kröger-Vink notation to describe the reaction leading to formation of ionic vacancy defects that could form instead of the electronic defects that you considered in part (b), again assuming that only one of the possible defect types forms.
e. If the defect reaction that you wrote in part (d)occurs in the material, what dependence of the conductivity on partial pressure of oxygen would you expect to see in your new solid solution material?
f. Considering your answers to parts (c) and (e) above, briefly describe a simple experimental procedure that you would use to determine whether your solid solution is electronically or ionically conductive.
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