Mischkristall

Mischkristall, also called mixed crystal, is a crystalline solid solution in which atoms of a solute occupy lattice sites within a host crystal, producing a single, homogeneous phase. The term covers both substitutional solid solutions, where solute atoms replace host atoms, and interstitial solid solutions, where smaller atoms fit into interstitial spaces without altering the overall lattice.

In substitutional systems, solute atoms must be similar in size and valence to the host atoms; common metal examples include copper–zinc alloys (brass) and nickel-based alloys that form substitutional solid solutions. In interstitial systems, small atoms such as carbon, nitrogen, or hydrogen reside in interstices of a metal lattice, as in carbon in iron forming steel or cast irons; this often leads to substantial strengthening.

Solubility of components in a Mischkristall is temperature- and composition-dependent and is described by phase diagrams. The Hume-Rothery rules summarize conditions for substantial solubility: atomic size difference within roughly 15%, the same crystal structure, similar electronegativity, and compatible valence. If solubility is limited, a miscibility gap or second phases can form, yielding a heterogeneous mixture.

A Mischkristall is central to metallurgy and materials science, enabling the tuning of properties such as strength, hardness, and ductility through alloying.