Diffusivity vs Temperature:
At room temperature, the inter-solid diffusivity is quite low and for all practical purposes the atoms can be considered as immobile. The typical temperatures employed are 900 to 1200 oC. The diffusivity in solid state is related to the temperature by Arrhenius equation  where D0 is the pre-exponent and EA is the activation energy. This is valid for solid-solid diffusion. It may be worth mentioning that, for gases, the dependence of diffusivity on temperature is given by . Hence, the inter-solid diffusivity coefficient will increase significantly with an increase in the temperature.