ASampleTest2 - 1 A Sample Test TiO2 has been developed as...

A Sample Test
1. TiO
2
has been developed as an oxygen sensor material based on the its electronic
conductivity dependence on oxygen pressure. The electronic conductivity is
proportional to the electron concentrations in the crystal. Experimental
measurements showed that in oxygen-deficient Titania (TiO
2-x
) in which the defect
concentrations are controlled by the reduction reaction, the electronic conductivity is
proportional to minus fifth power of oxygen pressure, i.e.,
n electron concentration
( )
∝ p
O
2
− 1 5
There are two possible reduction mechanisms in TiO
2-x
: (1) the oxygen deficiency is
accommodated by oxygen vacancies; and (2) the oxygen deficiency is caused by
titanium interstitials.
(a) Write the defect reactions for the two possible reduction mechanisms.
(b) Based on the above dependence of electron concentration on oxygen pressure,
determine which of the two is the dominant mechanism?
2. Discuss the three regimes of grain boundary diffusion, A, B and C, as classified by
Harrison:
(a)