In materials chemistry, a binary phase or binary compound is a chemical compound containing two different elements. Some binary phase compounds are molecular, e.g. carbon tetrachloride (CCl₄). More typically binary phase refers to extended solids. Famous examples zinc sulfide, which contains zinc and sulfur, and tungsten carbide, which contains tungsten and carbon.^[1]

Phases with higher degrees of complexity feature more elements, e.g. three elements in ternary phases, four elements in quaternary phases. These phases exhibit a higher degree of complexity due to the interaction of these elements at different conditions.