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Since crystals grow from liquid and glassy states, the liquid structure feature may also exist in the pair-correlation functions of crystalline systems. The present article addresses the spherical-periodic order derived from Friedel oscillations in the pair-correlation functions of simple crystal structures such as face-centered cubic, hexagonal close-packed, and body-centered cubic structures. In these simple crystal structures, the resonance lattice planes, corresponding to the strong peaks in reciprocal space, give the Friedel wavelengths using their interplanar spacings, which are {111} and {200} for the face-centered cubic structure, {100}, {002}, and {101} for the hexagonal close-packed structure, and {110} for the body-centered cubic structure. After being scaled with the Friedel wavelengths corresponding to the most intense diffraction peaks, the pair-correlation functions all show atomic density maxima within the spherical-periodic zones. From such a spherical-periodic picture of any simple crystal structure, it is possible to identify a charge-neutral and mean-density local atomic entity that serves as the molecule-like structural unit of the whole structure. Examples in Cu-Zn, Co-Cr, and β-Ti alloys are provided to show how to interpret the compositions of simple-crystal-based industrial alloys.

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Reaching simultaneously high mechanical strength and low electrical resistivity is difficult as both properties are based on similar microstructural mechanisms. In our previous work, a new parameter, the tensile strength-over-electrical resistivity ratio, is proposed to evaluate the matching of the two properties in Cu alloys. A specific ratio of 310 × 108 MPa·Ω−1·m−1, independent of the alloy system and thermal history, is obtained from Cu-Ni-Mo alloys, which actually points to the lower limit of prevailing Cu alloys possessing high strength and low resistivity. The present paper explores the origin of this specific ratio by introducing the dual-phase mechanical model of composite materials, assuming that the precipitate particles are mechanically mixed in the Cu solid solution matrix. The strength and resistivity of an alloy are respectively in series and parallel connections to those of the matrix and the precipitate. After ideally matching the contributions from the matrix and the precipitate, the alloy should at least reach half of the resistivity of pure Cu, i.e., 50%IACS, which is the lower limit for industrially accepted highly conductive Cu alloys. Under this condition, the specific 310 ratio is related to the precipitate-over-matrix ratios for strength and resistivity, which are both two times those of pure Cu.