Chapter 17: Metallic Structures I: Simple, Derivative, and Superlattice Structures

The foundation establishes the three primary metallic lattice types—face-centered cubic, body-centered cubic, and hexagonal close-packed—along with their geometric properties and X-ray diffraction signatures. The chapter explains how atomic packing efficiency and interatomic spacing are calculated using theoretical pair potential models to predict equilibrium structures. A central focus addresses alloy formation through the Hume-Rothery rules, which establish criteria for solid solubility based on atomic size compatibility, electronegativity differences, and valency relationships, complemented by Vegard's law for predicting how lattice parameters change as composition varies in solid solutions. The text systematically categorizes derivative structures according to their parent lattices, describing ordered fcc-based phases such as the L1-2 and L1-0 types exemplified by copper-gold systems, along with interstitially modified structures including diamond cubic, zinc-blende, and fluorite arrangements common in semiconductors and ionic materials. Bcc-derived structures receive detailed treatment, including the cesium chloride B2 prototype and magnetic Heusler alloys, while hcp-derived variants such as wurtzite and nickel arsenide are analyzed in relation to atomic stacking sequences and resulting crystal environments. The chapter proceeds to superlattice formation, explaining how temperature-driven order-disorder transitions create sublattice arrangements and generate anti-phase boundaries that mark transitions between ordered domains, with complex stacking sequences generating long-period superstructures. Advanced topics encompass synthetically created modulated structures produced through thin-film deposition, magnetic phenomena in artificial multilayered systems, and detection of incommensurate modulations and quasiperiodic ordering through satellite peak analysis in diffraction experiments. The treatment concludes with practically important interstitial systems including steel microstructures and metal hydride compounds.