5. The conductivity of titanium dioxide, TiO2, at 1166 K was found to depend upo

Question

5. The conductivity of titanium dioxide, TiO2, at 1166 K was found to depend upon the oxygen partial pressure as in the following table. Assuming that oxygen vacancies are introduced into the oxide as the main point defect, is the vacancy more likely to be doubly or singly charged? Conductivity/S m1 .047 5.012 7.94 15.85 39.81 83.18 Oxygen Partial Pressure/atm 1.0× 10 2 1.58 x 10-6 1.0 x 107 1.58 x 109 5.01 x 10~12 7.94 × 10-14 Data adapted from J. Novotny, M. Radecka, and M. Rekas, J. Phys. Chem

Explanation / Answer

Point Defect is a vacancy in a lattice created by a missing atom or ion, since it is assumed that the oxygen vacancies in the oxide are the main point defects, and the conductivity of the compound Ti02 depends on the oxygen partial pressure, therefore, as we can observe in the given table that for higher values of conductivity the oxygen partial pressure is slightly higher than for the lower values of conductivity, that means the vacancy in the crystal structure depends not only upon the missing atom or ion, but also of the conductivity of that ion or atom which makes the vacancy singly or doubly charged. In the given table, for any two lower values of conductivity we have same values of oxygen partial pressure but having different magnitudes, so if an atom or an ion leaves the crystal structure it will create a vacany or a void in the structure which will be doubly charged, we deduce it from the given as the two values of oxygen partial pressure corresponds to double charge of the same vacany in the structure.   

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