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Ionic Crystals (ionic + crystal)
Selected AbstractsInfrared Spectra of Hydrogen-Bonded Ionic Crystals: Ab initio Study of Mg(OH)2 and ,-Be(OH)2.CHEMINFORM, Issue 45 2004Piero Ugliengo Abstract For Abstract see ChemInform Abstract in Full Text. [source] First-Principles Calculations of Anion Vacancies in Oxides and NitridesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002Isao Tanaka The formation energy, structural relaxation, and defect-induced states of neutral anion vacancies of five oxides (i.e., MgO, Al2O3, ZnO, In2O3, and SnO2) and four nitrides (i.e., AlN, Si3N4, Ge3N4, and InN) are systematically discussed, based on first-principles plane-wave pseudopotential calculations. Two types of polymorphs for each compound are compared. The number of atoms included in the supercells ranged from 54 to 96. When a localized vacancy-induced state appears within the band gap, as in a typical ionic crystal, the formation energy can be well scaled by the band gap of the perfect crystal. On the other hand, when an empty and localized vacancy-induced state is located above the highest occupied band or no localized state is formed, the formation energy has a tendency to be smaller. In compounds such as ZnO and SnO2, the formation energy is dependent largely on the crystal structure. This result can be explained by the transition of the vacancy-induced state from occupied to unoccupied, which is caused by the change in atomic arrangement, as represented by the cation coordination number. [source] Models for the treatment of crystalline solids and surfacesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2004Karl Jug Abstract Crystalline solids and surfaces have become a subject of growing interest. The difficulty of a comprehensive description of a variety of phenomena by a single method has led to the development of many models. These models can be classified as nonperiodic and periodic models. The former include free clusters, saturated clusters, and embedded clusters. The latter two models serve to remove the boundary effects of the free clusters. No perfect avoidance of such effects can be achieved in this way. The cyclic cluster model overcomes this difficulty in a natural way. It is periodic with a finite periodicity. An embedding can take into account a long-range effect in ionic crystals. Previous periodic approaches relied on the large unit cell model, which is related to the supercell approach. For perfect crystals the conventional unit cell approach is a well-known standard. However, its disadvantage is the unphysical periodicity of defects, which is avoided in the cyclic cluster model. The present article presents a description of these models together with selective applications to solid-state systems and surfaces. © 2004 Wiley Periodicals, Inc. J Comput Chem 13: 1551,1567, 2004 [source] A single law for the activation energies of self-diffusion of various cubic metals, intermetallic compounds, ionic crystals and oxidesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2007Hans Siethoff Abstract In previous publications the author put forward a relation which, for face-centred cubic metals and intermetallic compounds with B2 and L12 structures, connected the activation energy of self-diffusion with lattice constant and shear modulus. It is one aim of the present study to show that this formalism can be extended to intermetallic compounds with C1, D03 and C15 crystal structures. Since the covalently bonded cubic semiconductors and ceramics obey a different law, the question concerning the influence of the chemical bond was additionally investigated. Therefore ionic crystals and oxides with B1, B2 and C1 structures were analysed. It is demonstrated that these materials obey the same law as the metals and intermetallic compounds, for the B1 structure, however, the prefactor of the common rule is different. To be able to evaluate such differences, the proposed relation had to be more quantitatively derived than it was done before. Some cubic transition metals do not fit in the general picture. The deviations are traced back to the binding properties of the electronic d-bands. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||