First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling

Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing. (C) 2017 Elsevier B.V. All rights reserved

Preparation of Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites and their controlled magnetic properties

Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites with cation compositions Sr0.5Ca0.2Nd0.3Fe12.0-x(Al0.5Co0.5)xO19 were synthesized using the traditional ceramic process by varying AlCo content (x) (0.0 ≤ x ≤ 0.5). The microstructures, morphologies and ferromagnetic properties of the samples were investigated as a function of AlCo content (x) by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transformer infrared (FT-IR) spectroscopy and Hysteresis graph meter. The X-ray diffraction patterns show that the hexaferrites with AlCo content (x) of 0.0 ≤ x ≤ 0.2) exhibited M-type phase and α-Fe2O3 as impurity phase, while the hexaferrites with AlCo content (x) ≥ 0.3 exhibited the single M-type phase. XRD, along with FT-IR analysis confirmed the formation of M-type hexaferrites and the successful substitution of Al3+ and Co2+ ions in the hexaferrite lattice. The results of FE-SEM images proposed that all the particles with regular hexagonal platelet-like shape were homogeneous dispersed. The remanence (Br) first increased with AlCo content (x) from 0.0 to 0.3, and then decreased when AlCo content (x) ≥ 0.3. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first increased with AlCo content (x) from 0.0 to 0.2, and then decreased with AlCo content (x) from 0.2 to 0.3, and increased when AlCo content (x) ≥ 0.3. Maximum energy product [(BH)max] first increased with AlCo content (x) from 0.0 to 0.2, and then decreased at AlCo content (x) ≥ 0.2. Squareness ratio (Hk/Hcj) decreased with increasing AlCo content (x) from 0.0 to 0.5