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Ivanovskii A.L.,RAS Institute of Solid State Chemistry
International Journal of Refractory Metals and Hard Materials

The high-level ab initio calculations of elastic moduli of materials now become a routine procedure, and the renewed attention is paid to the semi-empirical macroscopic models, providing the correlations between the Vickers hardness HV and some elastic moduli. Such correlations, building up a bridge between Vickers hardness and elastic parameters, seem a helpful way to semi-quantitative estimations of hardness and to theoretical search of novel hard materials, based on the calculations of their elastic properties. Here, using the results of our calculations of elastic parameters of 14 hexagonal AlB2-like diborides of s, p and d metals MB2 (where M = Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W), we have probed six recently proposed correlations between HV and bulk (B), shear (G), Young's moduli (E), as well as Poisson's ratio (ν), and the parameter k (the G/B ratio), and we compare the obtained results with the available experimental data. Our analysis reveals that for this family of related materials the correlations HV ~ G, and HV ~ E will be the most suitable approximations which enable us to roughly evaluate the Vickers hardness of diborides numerically. © 2012 Elsevier Ltd. Source

Rempel A.,RAS Institute of Solid State Chemistry | Magerl A.,Friedrich - Alexander - University, Erlangen - Nuremberg
Acta Crystallographica Section A: Foundations of Crystallography

Experimentally it is observed that nanomaterials from II-VI compounds like CdS have a high density of stacking faults. It is argued that these are not crystal defects but rather that they represent a characteristic feature of nanomaterials. © 2010 International Union of Crystallography Printed in Singapore-all rights reserved. Source

Gusev A.I.,RAS Institute of Solid State Chemistry

The way in which nonstoichiometry and order and disorder interrelate in solid phase compounds is discussed. Nonstoichiometry due to the presence of structural vacancies is widely found in such solid phase compounds as transition metal carbides, nitrides, and oxides, and in related ternary interstitial compounds. It is shown that it is nonstoichiometry that determines the disordered or ordered distribution of atoms and vacancies. A review is given of the current status of research into structural order-disorder phase transitions in nonstoichiometric compounds with basal cubic and hexagonal crystal lattices. Symmetry analysis results for disorder-order and order-order phase transformations are considered in detail. Key superstructure types that form in nonstoichiometric compounds with vacancies in one or two sublattices are also described. © 2014 Uspekhi Fizicheskikh Nauk, Russian Academy of Sciences. Source

Ivanovskii A.L.,RAS Institute of Solid State Chemistry
Russian Chemical Reviews

The review generalizes information on methods for modification of graphene-based carbon materials through creation of structural defects, introduction of sub-stitutional impurities, adsorption of impurity atoms and mechanical deformations. Graphene ribbons and nano-flakes, graphene allotropes, as well as multi-layer graphenes and graphene-containing hybrid carbon structures are considered. Methods of synthesis and the results of studies on the properties and simulation of graphene derivatives (graphane, graphone and fluorographene) are discussed. The results obtained in studies of related non-carbon graphene-like materials including silicon-, germanium-and tin-based structural analogues of graphene, graphene-like binary phases SiC, GeC, SiGe, SiSn, etc., as well as compounds AIIIBV (white graphene, etc.) and AIIBVI (BeO, ZnO, ZnS) are generalized. Other graphene-like materials including metal dichalcogenides, oxides and car-bides are briefly outlined. The bibliography includes 605 references. © 2012 Russian Academy of Sciences and Turpion Ltd. Source

Ivanovskii A.L.,RAS Institute of Solid State Chemistry
Physica C: Superconductivity and its Applications

Very recently, the first ThCr 2Si 2-type ternary superconductor K 0.8Fe 2Se 2 with enhanced T C ∼ 31 K has been discovered. This finding has stimulated much activity in search for related materials and triggered intense studies of their properties. Indeed, very soon superconductivity (T C ∼ 28-32 K) was also found in the series of related ternary systems (so-called 122 phases) such as Cs xFe 2-ySe 2, Rb xFe 2-ySe 2, (TlK) xFe ySe 2, and (TlRb) xFe ySe 2, which formed a new group of superconducting iron-based materials without toxic As. In this paper the recent progress in synthesis of 122-like iron-selenide systems and in experimental research of their properties is reviewed. Available theoretical data on electronic, magnetic, and elastic properties of this newest group of superconducting materials are also discussed. © 2011 Elsevier B.V. All rights reserved. Source

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