= Solution
Write the <Arrhenius equation> as $D=D_0e^{-Q/(k_BT)}$. Eliminating the prefactor with two temperatures gives
$$
Q=\frac{k_B\ln(D_{600}/D_{300})}{1/T_{300}-1/T_{600}}
\quad\Longrightarrow\quad
\boxed{Q=0.795\,\mathrm{eV}=76.7\,\mathrm{kJ\,mol^{-1}}}.
$$
Use absolute temperatures $573.15$ and $873.15\,\mathrm K$. Because the input is a vacancy <diffusion coefficient>, this is a migration <activation energy> inferred from that diffusivity; an additional vacancy-formation energy should not automatically be added.
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