Solutions to exercises
71
Solutions to exercises
Solution 2.1 – Determination of conductivity by four-electrode method
1. Figure 27 shows the potential difference V B − V C as a function of the current I passing through the cell. The curve is linear and is given by
V B − V C = 0.0422 # I
with V B − V C in mV and I in mA.
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9
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Figure 27 – Potential difference V B − V C as a function of current I.
This linear variation indicates that La 0.8 Sr 0.2 MnO 3−δ is ohmic under the
given measurement conditions.
2. The resistance R 1 between points B and C corresponds to the slope of the
line and is given by
R 1 = 0.0422 Ω
3. The conductivity of La 0.8 Sr 0.2 MnO 3−δ is given by the relation
R
k
0.0422
7.59
σ =
=
179.9 S cm
1
σ =
−
4. a. Table 18 gives the data required to plot the conductivity in the form
log σT = f(1/T).