arXiv subjects

Arslan B. Mazitov

Publications and source records attributed to Arslan B. Mazitov.

4 recordsLinked to original sources

arXiv2021

Sr-Doped Molecular Hydrogen: Synthesis and Properties of SrH$_{22}$

Recently, several research groups announced reaching the point of metallization of hydrogen above 400 GPa. Following the mainstream of extensive investigations of compressed polyhydrides, in this work we demonstrate that small (4 atom %) doping of molecular hydrogen by strontium leads to a dramatic reduction in the metallization pressure to about 200 GPa. Studying the high-pressure chemistry of the Sr-H system at 56-180 GPa, we observed the formation of several previously unknown compounds: C2/m-Sr$_3$H$_{13}$, pseudocubic SrH$_6$, SrH$_9$ with cubic F-43m Sr sublattice, and pseudotetragonal P1-SrH$_{22}$, the metal hydride with the highest hydrogen content discovered so far. Unlike Ca and Y, strontium forms molecular semiconducting polyhydrides, whereas calcium and yttrium polyhydrides are high-Tc superconductors with an atomic H sublattice. The latter phase, SrH$_{22}$ or Sr$_{0.04}$H$_{0.96}$, may be considered as a convenient model of the consistent bandgap closure and metallization of hydrogen. Using the impedance measurements in diamond anvil cells at 300-440 K, we estimated the direct bandgap of the Pm-3n-like compound P1-SrH$_6$ to be 0.44-0.51 eV at 150 GPa, and its metallization pressure to be 220 GPa. Together with the machine learning interatomic potentials, the impedance spectroscopy allowed us to estimate the diffusion coefficients of hydrogen D$_H$ = 1.0-2.8 E-10 m$^2$/s in SrH$_6$ and 1.2-2.1 E-9 m$^2$/s in P1-SrH$_{22}$ at 500-600 K.

cond-mat.mtrl-sci↗

arXiv2021

Grain boundaries in minerals: atomic structure, phase transitions, and effect on strength of polycrystals

Grain boundaries (GBs) and interfaces in polycrystalline materials are significant research subjects in the field of materials science. Despite a more than 50-year history of their study, there are still many open questions. The main challenge in studying interfacial structures is the extreme complexity of their experimental and theoretical observation and description. The presence of phase-like states at grain boundaries called complexions requires even more effort in their study. Here, we demonstrate the effect of grain boundaries on the properties of polycrystalline minerals on the example of the $Σ$5[310](001) grain boundary in periclase (MgO). Using the combination of extended evolutionary algorithm USPEX and modern machine-learning interatomic potentials, we explore the configuration space of the specified grain boundary and predict its possible phase-like states. In addition to the widely studied CSL-type structure, we found several stable GB complexions with various atomic densities at the boundary plane. Analysis of grain boundary excess volume of the structures revealed the successive stages of GB failure under the tensile applied in the normal direction of the boundary plane. Our results demonstrate that interfacial chemistry and structural diversity can be surprisingly rich even in seemingly simple and thoroughly investigated materials. The phenomena we observe here are not specific to MgO and should be general.

cond-mat.mtrl-sci↗

arXiv2021

Evolutionary algorithm for prediction of the atomic structure of two-dimensional materials on substrates

Today the study of two-dimensional (2D) materials has become one of the key objectives of materials science. Unlike their three-dimensional counterparts, 2D materials can simultaneously demonstrate unique transport and mechanical properties due to their dimensionality and quantum size effect. In their fabrication and application, 2D materials are usually located on top of the substrate or combined into heterostructures, which makes their structures and properties strongly depend on the nature and quality of the environment. Here, we present a novel method for studying the atomic structures of two-dimensional materials and epitaxial thin films on arbitrary substrates. The method can predict successful stages of epitaxial growth and the regions of stability of each atomic configuration with experimental parameters of interest. We demonstrate the performance of our methodology in the prediction of the atomic structure of MoS2 on Al2O3 (0001) substrate. The method is also applied to study the CVD growth of graphene and hexagonal boron nitride on Cu (111) substrates. In both cases, stable monolayer and multilayer structures were found. The stability of all the structures in terms of partial pressures of precursors and temperature of growth is predicted within the ab initio thermodynamics approach.

cond-mat.mtrl-sci↗

arXiv2018

Titanium-hydrogen interaction at megabar pressure

The process of transport of metal particles ($\mathit{ejecta}$) in gases is the subject of recent works in the field of nuclear energetics. We studied the process of dissolution of titanium ejecta in warm dense hydrogen at megabar pressure. Thermodynamic and kinetic properties of the process were investigated using classical and quantum molecular dynamics methods. We estimated the dissolution time of ejecta, the saturation limit of titanium atoms with hydrogen and the heat of dissolution. It was found that particles with a radius of 1 $μm$ dissolve in hydrogen in time of $1.5 \cdot 10^{-2} \ μs$, while the process of mixing can be described by diffusion law. The presented approach demonstrates the final state of the titanium-hydrogen system as a homogenized fluid with completely dissolved titanium particles. This result can be generalized to all external conditions under which titanium and hydrogen are atomic fluids.

cond-mat.mtrl-sci↗