The orientation relationship and the interfaces of ZrO₂(c)–CaZrO₃ unidirectional solidified eutectics have been investigated by means of electron diffraction and transmission electron microscopy (TEM). In contrast to previous studies on lamellar oxide-oxide systems, neither a constant orientation relationship between contiguous lamellae nor low-index interfaces are observed in this eutectic. As for metals and plastic crystals, it displays incoherent interfaces and nonfaceted growth. This unusual behavior is discussed in terms of entropy of fusion and related to the presence of oxygen vacancies in the ZrO₂(c) phase.