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Nanocrystalline Ni can adopt a hexagonal close-packed (hcp) structure,which does not appear in a bulk form under any conditions.Structural studies found its $>$ 20% expansion of volume per atom compared with face-centered cubic (fcc) Ni.Hard x-ray photoemission spectroscopy of the hcp phase revealed a $>$ 0.14 valence electron transfer from 3$d$ to 4$s$ and 4$p$ orbitals and a 0.25 eV reduction in band energy per electron compared with the fcc phase.Its nonmagnetic nature was attributed to a low density of states at the Fermi level.Thermodynamic stability of the hcp phase can be explained by the band energy gain and the electrostatic potential energy loss as related to the large lattice expansion.
High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transit
Materials with negative thermal expansion (NTE), which contract upon heating, are of great interest both technically and fundamentally. Here, we report giant NTE covering room temperature in mechanically milled antiperovksite GaNxMn3 compounds. The m
Bulk, shear, and compressional aggregate sound velocities of hydrogen and helium in the close- packed hexagonal structure are calculated over a wide pressure range using two complementary approaches: semi-empirical lattice dynamics based on the many-
Piezoelectrics interconvert mechanical energy and electric charge and are widely used in actuators and sensors. The best performing materials are ferroelectrics at a morphotropic phase boundary (MPB), where several phases can intimately coexist. Swit
Transition metals, Fe, Co and Ni, are the canonical systems for studying the effect of external perturbations on ferromagnetism. Among these, Ni stands out as it undergoes no structural phase transition under pressure. Here we have investigated the l