Crystallization of 4He in Aerogel with Warming

Crystallization of 4He in a 96% porosity aerogel occurred both on warming and on cooling. However, crystallization stopped halfway while warming and did not continue to fill the aerogel, in contrast to crystallization while cooling. The crystallization with cooling is related to the global mass flow in the surrounding crystals, whereas the crystallization with warming is likely to be an annealing process via the diffusion of vacancies, which becomes more efficient at high temperatures.