Figure 2: Location and shape of liquid/solid interface visualized at different stages of the crystal growth.

(a) Neutron transmission images of BaBrCl:5%Eu sample during the crystal growth procedure. Images are integrated over 30 minutes and acquired for neutrons in the energy range of 9.76 meV – 31.10 meV. The time since the start of crystal growth is indicated in each image. A brighter horizontal line in the middle of the sample corresponds to a slower growth rate when furnace temperature was held nearly constant between hours 3 and 4. The calibration bar indicates the sample transmission. (b) The ratio of two consecutive images (30 min acquisition each) is shown to emphasize the location of interface between liquid and solid phases. The darker areas correspond to reduced Eu concentration relative to the previously acquired image as the Eu is rejected by the growing interface into the liquid by normal segregation. (c) – same as (b) except for the sample with 0.5 mole % Eu doping, 1 hour image integration time. The movies S1 and S2 in the online Supporting information show the dynamics of interface observed during crystal growth.