In a $1970$ paper on the diffusivity of gold in lithium, Ott begins,

"The diffusion of noble metal tracers in Li has been found to be very fast and not readily explicable by vacancy$-$based diffusion models. A discussion has been given, proposing an explanation of the fast diffusivity in terms of at least partially interstitial solubility."

He then presents experimental data.

a$)$ What is a vacancy? Explain the vacancy model of diffusion.

b$)$ What is an interstitial?

c$)$ What equation describes diffusion?

He obtains the data in the first two columns.

d$)$ Complete the table above.

e$)$ Graph the data ln$($D$)$ vs $1000/$T$.$

f$)$ Determine the activation energy and diffusion coefficient at infinite temperature.