I completed my diploma work at Moscow State University in 2011 under the supervision of Prof. Evgeny Antipov and my PhD in the group of Prof. Yuri Grin at the Max Planck Institute for Chemical Physics of Solids in 2016. After a postdoctoral stay at the University of Delaware with Prof. Svilen Bobev, I joined the group of Prof. Anja-Verena Mudring at Stockholm University in the late 2018.
The essence of my research is the synthesis of new intermetallic compounds, study of their crystal and electronic structures, and relating those to the experimentally observed physical properties. Compounds of interest include materials with unusual magnetic behavior, for example, magnetically frustrated or low-dimensional magnets, as well as superconducting and thermoelectric materials. Conventional high-temperature annealing, arc-melting, and flux growth techniques are the primary synthetic tools utilized in my work. Crystal structures are examined using single-crystal and powder diffraction techniques, including measurements at large-scale facilities. Physical properties of intermetallics are interrogated by thermodynamic (magnetic susceptibility, heat capacity) and transport (electrical resistivity, thermal conductivity) measurements. Electronic structures and chemical bonding are analyzed employing first-principle calculations on the density functional theory level.
I urval från Stockholms universitets publikationsdatabas
Bismuth as a Reactive Solvent in the Synthesis of Multicomponent Transition-Metal-Bearing Bismuthides
2020. Alexander Ovchinnikov, Svilen Bobev. Inorganic Chemistry 59 (6), 3459-3470Artikel
Employment of liquid bismuth (Bi) allows the facile single-crystal growth of compounds containing elements with high melting points, provided that these elements have reasonably high solubility in Bi. Utilization of the Bi flux approach yielded two new ternary bismuthides, SrNi0.17(1) Bi-2[a defect variant of the BaCuSn2 type, space group Cmcm, a = 4.879(2) angstrom, b = 17.580(6) angstrom, and c = 4.696(2) angstrom] and CaTi3Bi4 [NdTi3 (Sn0.1Sb0.9)(4) structure type, space group Fmmm, a = 5.6295(7) angstrom, b = 9.8389(1) angstrom, and c = 23.905(3) angstrom]. In addition, the ternary antimonide CaV3Sb4, isostructural with CaTi3Bi4, was synthesized from antimony (Sb) flux, and analyzed with the goal of validating structural assessment of the bismuthide analogue, where the X-ray crystallographic work proved to be very challenging. All synthesized compounds exhibit complex crystal structures featuring quasi-two-dimensional building blocks of different topologies. First-principle calculations reveal hypervalent bonding in the homoatomic Bi subunits. Physical property measurements indicate metallic conductivity and the absence of localized magnetism in the studied compounds.
Exploration of Multi-Component Vanadium and Titanium Pnictides Using Flux Growth and Conventional High-Temperature Methods
2020. Alexander Ovchinnikov, Svilen Bobev. Frontiers in Chemistry 7Artikel
The flux growth method was successfully employed to synthesize millimeter-sized single crystals of the ternary barium vanadium pnictides Ba5V12As19+x (x approximate to 0.02) and Ba5V12Sb19+x (x approximate to 0.36), using molten Pb and Sb, respectively. Both compositions crystallize in space group P43m and adopt a structure similar to those of the barium titanium pnictides Ba(5)Ti(12)Pn(19+x) (Pn = Sb, Bi), yet with a subtly different disorder, involving the pnictogen and barium atoms. Attempts to obtain an arsenide analog of Ba(5)Ti(12)Pn(19+x) using a Pb flux technique yielded binary arsenides. High-temperature treatment of the elements Ba, Ti, and As in Nb or Ta tubes resulted in side reactions with the crucible materials and produced two isostructural compositions Ba8Ti13-xMxAs21 (M = Nb, Ta; x approximate to 4), representing a new structure type. The latter structure displays fcc-type metal clusters comprised of statistically distributed Ti and M atoms (M = Nb, Ta) with multi-center and two-center bonding within the clusters, as suggested by our first-principle calculations.
Metallic alloys at the edge of complexity
2020. Alexander Ovchinnikov, Volodymyr Smetana, Anja-Verena Mudring. Journal of Physics 32 (24)Artikel
Complex metallic alloys belong to the vast family of intermetallic compounds and are hallmarked by extremely large unit cells and, in many cases, extensive crystallographic disorder. Early studies of complex intermetallics were focusing on the elucidation of their crystal structures and classification of the underlying building principles. More recently, ab initio computational analysis and detailed examination of the physical properties have become feasible and opened new perspectives for these materials. The present review paper provides a summary of the literature data on the reported compositions with exceptional structural complexity and their properties, and highlights the factors leading to the emergence of their crystal structures and the methods of characterization and systematization of these compounds.
Studied and Forgotten. A Fresh Look at the Li-Mn-Ge System
2020. Alexander Ovchinnikov, Svilen Bobev. Zeitschrift für Anorganische und Allgemeines ChemieArtikel
The crystal structure of the ternary germanide Li2MnGe has been re-evaluated from single-crystal X-ray diffraction data. This compound crystallizes in a non-centrosymmetric superstructure of the ZrCuSiAs type (space group P4bm, Pearson code tP16), with the lattice parameters a = 6.088(4) angstrom, c = 6.323(4) angstrom. First-principle calculations for the idealized structure predict antiferromagnetic exchange in the square Mn nets and semimetallic ground state. In addition, a new ternary phase with the composition Li2-xMn4+xGe5 (x approximate to 1.2) was discovered. It adopts the V6Si5 structure type (space group Ibam, Pearson code oI44), with the lattice parameters a = 7.570(2) angstrom, b = 16.323(3) angstrom, c = 5.057(1) angstrom. DSC/TG measurements show that this compound is thermally stable below 995 K.
Layered Quaternary Germanides-Synthesis and Crystal and Electronic Structures of AELi(2)In(2)Ge(2) (AE = Sr, Ba, Eu)
2019. Alexander Ovchinnikov, Svilen Bobev. Inorganic Chemistry 58 (12), 7895-7904Artikel
Three new quaternary germanides with the composition AELi(2)In(2)Ge(2) (AE = Sr, Ba, Eu) have been synthesized and structurally characterized. The layered crystal structure of these phases features homoatomic In-In bonding, but there are no direct Ge-Ge bonds. Such a crystallographic arrangement can be regarded as an ordered quaternary derivative of the CaCu4P2 structure (trigonal syngony, Pearson code hR7). Comprehensive analysis of the structural genealogy suggests relationships with the structures of other layered pnictides and chalcogenides, which are discussed. Partitioning of the available valence electrons and the assignment of the formal charges indicate that the composition of the new germanides is charge-balanced. First-principles calculations and electrical transport measurements indicate poor metallic behavior, resulting from significant hybridization of the electronic states.
Multifaceted Sn-Sn bonding in the solid state. Synthesis and structural characterization of four new Ca-Li-Sn compounds
2019. Alexander Ovchinnikov, Svilen Bobev. Dalton Transactions 48 (38), 14398-14407Artikel
Four novel ternary phases have been prepared in the system Ca-Li-Sn using both the metal flux method and conventional high-temperature synthesis. Each of the obtained compositions represents its own (new) structure type, and the structures feature distinct polyanionic Sn units. Ca4LiSn6 (space group Pbcm, Pearson symbol oP44) accommodates infinite chains, made up of cyclopentane-like [Sn-5]-rings, which are bridged by Sn atoms. The Sn atoms in this structure are two- and three-bonded. The anionic substructure of Ca9Li6+xSn13-x (x approximate to 0.28, space group C2/m, Pearson symbol mS56) displays extensive mixing of Li and Sn and combination of single-bonded and hypervalent interactions between the Sn atoms. Hypervalent bonding is also pronounced in the structure of the third compound, Ca2LiSn3 (space group Pmm2, Pearson symbol oP18) with quasi-two-dimensional polyanionic subunits and a variety of coordination environments of the Sn atoms. One-dimensional [Sn-10]-chains with an intricate topology of cis- and trans-Sn-Sn bonds exist in the structure of Ca9-xLi2Sn10 (x approximate to 0.16, space group C2/m, Pearson symbol mS42), and the Sn-Sn bonding in this case demonstrates the characteristics of an intermediate between single- and double- bond-order. The peculiarities of the bonding are discussed in the context of the Zintl approach, which captures the essence of the main chemical interactions. The electronic structures of all four compounds have also been analyzed in full detail using first-principles calculations.