A unique parallel-to-vertical alternating layer microstructure is observed in the In/Ag2Se couples reacted at 723 K (450 degrees C). The reaction zone has two different regions. Both regions are composed of liquid and In4Se3 phases. The region adjacent to the Ag2Se substrate has alternating-layer structure, and the layers are aligned parallel to the reaction zone/Ag2Se interface. The phase growth direction changes abruptly in the other region and is nearly vertical at the end adjacent to the parallel region. (C) 2015 Elsevier B.V. All rights reserved.