arXiv subjects

Maxim Bykov

Publications and source records attributed to Maxim Bykov.

23 records · Page 2Linked to original sources

arXiv2019

Mott and spin-Peierls physics in TiPO$_4$ under high pressure

TiPO$_4$ is a Mott insulator and one of few inorganic compounds featuring a spin-Peierls phase at low temperature. Recent experimental studies have suggested the presence of spin-Peierls dimerization also at ambient temperature though at high pressure. Here, we present a combined experimental and theoretical study of the energetics of the high-pressure phase. We analyse dimerization properties and their coupling to spin degrees of freedom. Most importantly, we argue that TiPO$_4$ resents a direct analogue to the celebrated binary transition metal oxide VO$_2$. TiPO$_4$ allows to assess spin-dimer physics in the high-pressure regime in a controlled fashion, having the potential to become an important model system representative of the class of dimerized transition metal oxides.

cond-mat.str-el↗

arXiv2019

Inverse pressure-induced Mott transition in TiPO$_4$

TiPO$_4$ shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high pressure experiments for TiPO$_4$ reported two new structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053]. The latter was shown to include the first example of 5-fold O-coordinated P-atoms in an inorganic phosphate compound. In this work we characterize the electronic structure and other physical properties of these new phases by means of ab-initio calculations, and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.

cond-mat.str-el↗

arXiv2019

High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re$_{2}$(N$_{2}$)N$_{2}$ stable at ambient conditions

Here we report the synthesis of metallic, ultraincompressible (bulk modulus $K_{0}$ = 428(10) GPa) and very hard (nanoindentation hardness 36.7(8) GPa) rhenium (V) nitride pernitride Re$_{2}$(N$_{2}$)N$_{2}$. While the empirical chemical formula of the compound, ReN$_{2}$, is the same as for other known transition metals pernitrides, e.g. IrN$_{2}$, PtN$_{2}$, PdN$_{2}$ and OsN$_{2}$, its crystal chemistry is unique. The known pernitrides of transition metals consist of a metal in the oxidation state +IV and pernitride anions N$_{2}^{4-}$. ReN$_{2}$ contains both pernitride N$_{2}^{4-}$ and discrete N$^{3-}$ anions, which explains its exceptional properties. Moreover, in the original experimental synthesis of Re$_{2}$(N$_{2}$)N$_{2}$ performed in a laser-heated diamond anvil cell via a direct reaction between rhenium and nitrogen at pressures from 40 to 90 GPa we observed that the material was recoverable at ambient conditions. Consequently, we developed a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH$_{4}$N$_{3}$, in a large-volume press at 33 GPa. Our work resulted not only in a discovery of a novel material with unusual crystal chemistry and a set of properties attractive for potential applications, but also demonstrated a feasibility of surmounting conceptions common in material sciences.

cond-mat.mtrl-sci↗

arXiv2017

Structural stability and mechanism of compression of stoichiometric B13C2 up to 68 GPa

Boron carbide is a ceramic material with unique properties widely used in numerous, including armor, applications. Its mechanical properties, mechanism of compression, and limits of stability are of both scientific and practical value. Here, we report the behavior of the stoichiometric boron carbide B13C2 studied on single crystals up to 68 GPa. As revealed by synchrotron X-ray diffraction, B13C2 maintains its crystal structure and does not undergo phase transitions. Accurate measurements of the unit cell and B12 icosahedra volumes as a function of pressure led to conclusion that they reduce similarly upon compression that is typical for covalently bonded solids. A comparison of the compressional behavior of B13C2 with that of alpha-B, gamma-B, and B4C showed that it is determined by the types of bonding involved in the course of compression. Neither molecular-like nor inversed-molecular-like solid behavior upon compression was detected that closes a long-standing scientific dispute.

cond-mat.mtrl-sci↗

arXiv2017

First non-icosahedral boron allotrope synthesized at high pressure and high temperature

Theoretical predictions of pressure-induced phase transformations often become long-standing enigmas because of limitations of contemporary available experimental possibilities. Hitherto the existence of a non-icosahedral boron allotrope has been one of them. Here we report on the first non-icosahedral boron allotrope, which we denoted as ζ-B, with the orthorhombic α-Ga-type structure (space group Cmce) synthesized in a diamond anvil cell at extreme high-pressure high-temperature conditions (115 GPa and 2100 K). The structure of ζ-B was solved using single-crystal synchrotron X-ray diffraction and its compressional behavior was studied in the range of very high pressures (115 GPa to 135 GPa). Experimental validation of theoretical predictions reveals the degree of our up-to-date comprehension of condensed matter and promotes further development of the solid state physics and chemistry.

cond-mat.mtrl-sci↗