arXiv subjects

Viktor Soprunyuk

Publications and source records attributed to Viktor Soprunyuk.

3 recordsLinked to original sources

arXiv2023

Phase transition at 350 K in the Ti$_3$C$_2$T$_x$ MXene: possible sliding (moiré) ferroelectricity

A phase transition is found in Ti$_3$C$_2$T$_x$ MXene at 350 K, by measuring the complex Young's modulus of self-standing thick films. A step-like softening and increase of the mechanical losses is found below 350 K, indicative of a phase transition, where the square of the order parameter is coupled to strain. It is argued that it should be a ferroelectric transition, most likely of the sliding (moiré) type, due to charge transfer between facing flakes sliding with respect to each other. If the transition will be confirmed to be ferroelectric, Ti$_3$C$_2$T$_x$ will be added to the class of metallic ferroelectrics and open new perspectives of applications, in addition to the numerous already studied.

cond-mat.mtrl-sci↗

arXiv2022

Structure-dynamics relationships in cryogenically deformed bulk metallic glass

The atomistic mechanisms occurring during the processes of aging and rejuvenation in glassy materials involve very small structural rearrangements that are extremely difficult to capture experimentally. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in Cu44Zr44Al8Hf2Co2 bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. Using a measure of the configurational entropy calculated from the X-ray pair correlation function, the structural footprint of the deformation-induced rejuvenation in bulk metallic glass is revealed. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. This opens hitherto unavailable experimental possibilities allowing to unambiguously correlate changes in atomic configuration and structure to calorimetrically observed signals and can attribute those to changes of the dynamic and vibrational relaxations (α-, β- and γ-transition) in glassy materials. The results suggest that the structural footprint of the β-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the β-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature γ-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.

cond-mat.mtrl-sci↗

arXiv2005

Faraday Instability in a Surface-Frozen Liquid

Faraday surface instability measurements of the critical acceleration, a_c, and wavenumber, k_c, for standing surface waves on a tetracosanol (C_24H_50) melt exhibit abrupt changes at T_s=54degC above the bulk freezing temperature. The measured variations of a_c and k_c vs. temperature and driving frequency are accounted for quantitatively by a hydrodynamic model, revealing a change from a free-slip surface flow, generic for a free liquid surface (T>T_s), to a surface-pinned, no-slip flow, characteristic of a flow near a wetted solid wall (T < T_s). The change at T_s is traced to the onset of surface freezing, where the steep velocity gradient in the surface-pinned flow significantly increases the viscous dissipation near the surface.

physics.flu-dyn↗