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Linnikov O.D.,RAS Institute of Solid State Chemistry
Russian Chemical Reviews | Year: 2014

The models of formation of salt precipitates during crystallization from supersaturated aqueous solutions are analyzed. The results of theoretical simulations and experimental studies are compared. The attention is focused on the processes of crystal aggregation and agglomeration. The data on the mechanism of crystal intergrowth under conditions of mass crystallization of salts from supersaturated aqueous solutions are considered. The intergrowth process is shown to be described most reliably by the model based on the Polak theory according to which in supersaturated solutions, connecting nucleus-bridges are formed within aggregates between the closest faces of neighbouring crystals. © 2014 Russian Academy of Sciences and Turpion Ltd.

Gusev A.I.,RAS Institute of Solid State Chemistry
Journal of Solid State Chemistry | Year: 2013

A cubic model of Ti5O5 (Ti5O 5□=Ti9018O90□18) superstructure of nonstoichiometric titanium monoxide TixO z with double structure imperfection is proposed for the first time on the basis of symmetry analysis. The unit cell of the cubic superstructure Ti5O5 has a triple lattice constant as compared with that of the basic disordered B1 structure of TixOz monoxide and belongs to the space group Pm3̄m with regard to symmetry. The disorder-order TixOz (space group Fm3̄m) - Ti 5O5 (space group Pm3̄m) phase transition channel includes 75 superstructure vectors of seven stars {k10}, {k 7}, {k6(1)}, {k6(2)}, {k4(1)}, {k4(2)}, and {k1}. The distribution functions of Ti and O atoms on the sites of the model cubic superstructure Ti5O5 were calculated. Diffraction investigation of annealed ordered titanium monoxide TiO1.087 confirms the existence of the cubic (space group Pm3̄m) ordered phase Ti5O5. The cubic (space group Pm3̄m) superstructure Ti5O5 is shown to be a high-temperature structure with respect to the known monoclinic (space group C2/m) superstructure of the same type. © 2013 Elsevier Inc. All rights reserved.

Gusev A.I.,RAS Institute of Solid State Chemistry
Physics-Uspekhi | Year: 2014

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.

Ivanovskii A.L.,RAS Institute of Solid State Chemistry
International Journal of Refractory Metals and Hard Materials | Year: 2013

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.

Enyashin A.N.,RAS Institute of Solid State Chemistry | Ivanovskii A.L.,RAS Institute of Solid State Chemistry
Journal of Physical Chemistry C | Year: 2013

The properties of MXenes, a new group of quasi-2D d-metal carbide or nitride nanomaterials derived from the MAX phases by chemical exfoliation, can be very sensitive to the presence of surface functional groups. Herein, the MXenes Ti2C and Ti3C2 functionalized by methoxy groups are considered by means of the density functional theory tight-binding method. Their structural and electronic properties and relative stability are discussed in comparison with related and experimentally fabricated hydroxy derivatives of MXenes. © 2013 American Chemical Society.

Ivanovskii A.L.,RAS Institute of Solid State Chemistry
Progress in Solid State Chemistry | Year: 2013

In this paper, the experimental and theoretical results that may give an insight into the current status and possible prospects of the family of (sp 1 + sp2) hybridized carbon allotropes: graphynes (GYs) and graphdiynes (GDYs), are reviewed. These allotropes, which can form a rich variety of 0D-3D forms and demonstrate a set of distinguished properties, have attracted now increased attention and research interest as promising materials, which can compete in various potential applications with " conventional" sp2 carbon systems such as fullerenes, nanotubes or graphene and meet the increasing requirements to carbon-based nanomaterials. It can be seen from the increasing number of publications in the last five years that the interest in GYs and GDYs rapidly grows, and a lot of new results have been obtained today. For example, a set of 0D-3D forms of GYs and GDYs have been successfully synthesized and (or) predicted theoretically, and their key properties (structural, mechanical, electronic etc.) have been measured or estimated from ab initio calculations. This gives a strong impetus to further progress in applications of GYs and GDYs as materials for nanoelectronics, energy storage, as anode materials in batteries, as membranes for facilitating selective gas separation etc. All these efforts promote the expansion of the palette of promising carbon materials and accelerate the development of modern carbon-based technologies.

Rempel A.,RAS Institute of Solid State Chemistry | Magerl A.,Friedrich - Alexander - University, Erlangen - Nuremberg
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2010

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.

Ivanovskii A.L.,RAS Institute of Solid State Chemistry
Physica C: Superconductivity and its Applications | Year: 2011

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.

Ivanovskii A.L.,RAS Institute of Solid State Chemistry
Russian Chemical Reviews | Year: 2012

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.

The appreciable progress has been achieved currently in the development of design principles, synthesis, investigations and predictions of various groups of ultra-incompressible and superhard materials. One of the recently proposed families of these promising materials is represented by the diborides of heavy 4d and 5d metals. Along with experiments, the theoretical ab initio methods, which involve no a priori assumptions about the electronic structure and intra-atomic interactions, are very effective approaches in the determination and prediction of structural, mechanical, magnetic, optical, dielectric and superconducting properties of such materials. This paper offers a review of the recent advances in theoretical understanding and predictions of the mechanical properties (including elastic (reversible) deformations, which are related to compressibility, as well as the effects of plastic (irreversible) deformations, which are related to hardness of materials) as obtained by means of ab initio calculations - for a broad family of metal diborides MB2 (AlB 2-like diborides and the recently discovered diborides of heavy 4d and 5d metals with "puckered" boron sheets) and their relations to electronic, cohesive and bonding characteristics of these materials. © 2011 Elsevier Ltd. All rights reserved.

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