arXiv subjects

Konstantin Glazyrin

Publications and source records attributed to Konstantin Glazyrin.

At least 19 recordsLinked to original sources

arXiv2026

Pressure induced Electronic and Structural Transition in Ba$_2$NiTeO$_6$

This study explores the pressure evolution of the double perovskite Ba$_2$NiTeO$_6$ by employing experimental and computational techniques. For the study of structural and vibrational properties, synchrotron X-ray diffraction (XRD) and micro-Raman spectroscopic experiments at high-pressures were carried out. As a complementary study, DFT simulations of the structural properties as a function of pressure were performed to support and explain the experimental findings. Furthermore, the electronic and magnetic properties as a function of pressure were investigated using DFT. Our study reveals a structural phase transition from a rhombohedral $R\bar{3}m$ to a monoclinic $C2/m$ phase at high pressure, accompanied by a significant increase in bulk modulus. Certain anomalies were observed in Raman mode frequencies at lower pressures of about 1 GPa, indicating changes in the electronic structure with a modification from direct to indirect bandgap in the sample. A minimum in the Raman mode full-width-half-maximum (FWHM) at about 11 GPa, coincides with an increase in ordering in the sample, indicated by a drop in the distortion index of Ni-O$_6$ octahedra as well as a discontinuity in the $c/a$ ratio.

cond-mat.mtrl-sci↗

arXiv2026

Hydrogen uptake and hydride formation in Al$_x$CoCrFeNi high-entropy alloys: First-principles, universal-potential, and experimental study

Hydrogen uptake in complex multicomponent alloys, including high-entropy alloys (HEAs), governs both hydrogen storage capacity and resistance to hydrogen-induced degradation. We combine high-pressure experiments, density-functional theory (DFT), and a GRACE universal interatomic potential to investigate hydrogen absorption in Al$_{0.3}$CoCrFeNi and Al$_3$CoCrFeNi HEAs. In H$_2$ as a pressure-transmitting medium, the FCC Al$_{0.3}$CoCrFeNi alloy forms hydrides at ambient temperature above 3 GPa, whereas the Al-rich B2 Al$_3$CoCrFeNi alloy shows no evidence of hydride formation even upon heating at pressures up to 50 GPa. Experiments and calculations show that aluminum suppresses hydrogen uptake by increasing solution energies and destabilizing interstitial sites. The universal potential, employed in the calculations and pretrained on large DFT databases, closely reproduces DFT energetics and demonstrates transferability from the dilute limit to the hydride-forming regime. Simulations further disentangle the roles of local ordering, volume changes, composition, and crystal structure. Overall, our results indicate that hydrogen solubility in Al-containing HEAs is governed primarily by composition, with Al-driven B2 ordering as a strong secondary effect.

cond-mat.mtrl-sci↗

arXiv2025

Halogen Chains with One-Dimensional Semi-Metallic Electronic Structure and Peierls Physics in Polymorphs of Na4X5 (X = I, Br, Cl) Compounds

Since the pioneering works of Peierls, one-dimensional materials have attracted great attention. Still, the synthesis of truly monoatomic chains remains elusive. In this study, we explore a novel path of experimental synthesis of monoatomic one-dimensional chains by their chemical stabilization in ionic compounds. We demonstrate that in synthesized at high pressure sodium halides Na4X5 (X = I, Br, Cl) with hP18 Ga4Ti5-type structures, transfer of valence electrons from cations to anions leads to the formation of halogen chains connected with other atoms only by ionic interaction and having one-dimensional electronic structure. The Peierls physics in the systems is confirmed by theoretical calculations, newly synthesized incommensurately modulated i-hP18-Na4X5 (X = I, Br, Cl) compounds, as well as by the discovered hP36 phases of Na4Cl5 and Na4Br5.

cond-mat.mtrl-sci↗

arXiv2025

Compressional rate-dependent stability of ammonia hydrates crystallized from water-rich ammonia-water solutions

Understanding the crystallization pathways of water-rich ammonia-water (NH3-H2O) solutions and the stability of ammonia hydrates is key to unraveling the behavior of complex hydrogen-bonding networks as well as for planetary interior modelling. Yet, there are still inconsistencies in the crystallization sequence reported upon pressure-induced crystallization of H2O-rich NH3-H2O solutions at room temperature. Here, we investigate the effect of compression rates on the crystallization pathways of 25 wt% NH3 aqueous solutions at room temperature using dynamically compressed diamond anvil cells (dDAC) coupled with time-resolved X-ray diffraction. We show that compression rates exceeding 0.5 GPa/sec promote direct crystallization of a body-centered cubic (bcc) phase (DMA') with possible AMH stoichiometry coexisting with H2O ice VII, while rates below 0.2 GPa/sec stabilize monoclinic NH3-rich AHH-II and ice VII phases. Intermediate rates between 0.2-0.5 GPa/sec produce a mixture of both hydrates alongside ice VII, hence demonstrating the role of compression rate on the crystallization sequence of ammonia solutions. The compression behavior and phase stability of the distinct phase assemblies (AHH-II/DMA' + ice VII) are investigated further to place constraints on the composition of the DMA' phase, the effect of ice VII on the compressibility of ammonia hydrates, and the plausible incorporation of NH3 impurities within the lattice of high-pressure ice phases.

cond-mat.mtrl-sci↗

arXiv2025

Observation of Body-Centered Cubic Iron above 200 Gigapascals

The crystallographic structure of iron under extreme conditions is a key benchmark for cutting-edge experimental and numerical methods. Moreover, it plays a crucial role in understanding planetary cores, as it significantly influences the interpretation of observational data and, consequently, insights into their internal structure and dynamics. However, even the structure of pure solid iron under the Earth's core conditions remains uncertain, with the commonly expected hexagonal close-packed structure energetically competitive with various cubic lattices. In this study, iron was compressed in a diamond anvil cell to above 200 GPa, and dynamically probed near the melting point using MHz frequency X-ray pulses from the European X-ray Free Electron Laser. The emergence of an additional diffraction line at high temperatures suggests the formation of an entropically stabilized bcc structure. Rapid heating and cooling cycles captured intermediate phases, offering new insights into iron's phase transformation paths. The appearance of the bcc phase near melting at extreme pressures challenges current understanding of the iron phase diagram under Earth's core conditions.

cond-mat.mtrl-sci↗

arXiv2025

Hydrogen-rich hydrate at high pressures up to 104 GPa

Gas hydrates are considered fundamental building blocks of giant icy planets like Neptune and similar exoplanets. The existence of these materials in the interiors of giant icy planets, which are subject to high pressures and temperatures, depends on their stability relative to their constituent components. In this study, we reexamine the structural stability and hydrogen content of hydrogen hydrates, (H2O)(H2)n, up to 104 GPa, focusing on hydrogen-rich materials. Using synchrotron single-crystal X-ray diffraction, Raman spectroscopy, and first-principles theoretical calculations, we find that the C2-filled ice phase undergoes a transformation to C3-filled ice phase over a broad pressure range of 47 - 104 GPa at room temperature. The C3 phase contains twice as much molecular H2 as the C2 phase. Heating the C2-filled ice above approximately 1500 K induces the transition to the C3 phase at pressures as low as 47 GPa. Upon decompression, this phase remains metastable down to 40 GPa. These findings establish new stability limits for hydrates, with implications for hydrogen storage and the interiors of planetary bodies.

cond-mat.mtrl-sci↗

arXiv2025

Soft mode induced structural phase transition in Ba$_2$ZnTeO$_6$ at high pressure

In this paper, we present a thorough investigation of vibrational, structural, and electronic properties of perovskite-type rhombohedral Ba$_2$ZnTeO$_6$ (BZTO) under systematic application of pressure. To carry out the analysis, we have performed pressure-dependent Raman spectroscopic measurements, synchrotron XRD, and density functional theory-based calculations. At ambient conditions, BZTO stabilizes in $R\bar{3}m$ space group, which under pressure undergoes a structural transition to a monoclinic phase with space group $C2/m$ at around 18~GPa. In-depth Raman analysis reveals softening of a phonon mode E$_g$ ($\sim $ 28cm$^{-1}$) leads to the structural phase transition. First principle DFT calculations also indicate that the doubly degenerate soft mode associated with the in-phase TeO$_6$ octahedral rotation drives the structure to a lower symmetry phase $C2/m$.

cond-mat.mtrl-sci↗

arXiv2025

Structural transition and emission enhancement in vacancy ordered halide double perovskite Cs$_2$TeCl$_6$ under pressure

The effect of pressure on the structural evolution, enhancement of photoluminescence intensity and optical band gap of a vacancy ordered double halide perovskite Cs$_2$TeCl$_6$ is investigated systematically. We use synchrotron x-ray diffraction, Raman spectroscopy, optical band gap and photoluminescence measurements to explore the structural and the optical properties of Cs$_2$TeCl$_6$ under pressure up to 30.0 GPa. We find that Cs$_2$TeCl$_6$ undergoes a structural transition from cubic Fm$\bar{3}$m to monoclinic P2$_1$/n at very low pressure below 1.0 GPa. A significant increase in photoluminescence intensity and a rapid decrease in optical band gap are observed, which are related to the octahedral distortion and structural transition. Interestingly, with increasing pressure, the sample regains its ambient Fm$\bar{3}$m structure at around 3.4 GPa maintaining the cubic phase up to 30.0 GPa. The sample undergoes an iso-structural transition at around 14.1 GPa pressure with a slight decrease in compressibility.

cond-mat.mtrl-sci↗

arXiv2024

Emission enhancement and bandgap narrowing in $Cs_2TeBr_6$ under pressure

Pressure-induced emission enhancement and bandgap narrowing in vacancy-ordered halide double perovskite $Cs_2TeBr_6$ are extensively investigated through photoluminescence and absorption experiments. The below bandgap broad emission is attributed to self-trapped excitons recombination. The $Cs_2TeBr_6$ crystal, consisting of undistorted octahedra, exhibits substantial emission enhancement due to the lowering of the energy barrier between $^3P_1$ and self-trapped exciton states, as well as the suppression of nonradiative energy loss with increasing pressure. In the Raman measurements, the observed behavior of full width at half maximum of all Raman modes implies dominant electron-phonon interactions rather than anharmonic interactions between phonons. The pressure-dependent X-ray diffraction measurements reveal an anomalous behaviour in the normalized pressure as a function of the Eulerian strain.

cond-mat.mtrl-sci↗

arXiv2024

Resolving the pressure induced 'self-insertion' in skutterudite CoSb3

CoSb3, a skutterudite compound, is key in studying thermoelectric materials. Under compression, it undergoes a 'self-insertion' isostructural transition, redistributing large Sb atoms among crystallographic sites. We investigated CoSb3's structural stability up to 70 GPa using single crystal X-ray diffraction and high-resolution X-ray scattering, including Bragg Coherent Diffraction Imaging. We examined the material in three pressure transmitting media (PTMs), exploring how PTMs and nonhydrostatic stresses affect CoSb3. Notably, the 'self-insertion' transition may reduce or even make compressibility negative. Additionally, we report a previously unknown phase transformation from cubic Im-3 to trigonal R-3 above 40 GPa and discuss the phases' distinctive behaviors.

cond-mat.mtrl-sci↗

arXiv2024

High entropy alloys and their affinity to hydrogen: from Cantor to platinum group elements alloys

Properties of high entropy alloys are currently in the spotlight due to their promising applications. One of the least investigated aspects is the affinity of these alloys to hydrogen, its diffusion and reactions. In this study we apply high-pressure at ambient temperature and investigate stress-induced diffusion of hydrogen into the tructure of high entropy alloys HEA including the famous Cantor alloy as well as less known, but nevertheless important platinum group PGM alloys. By applying X-ray diffraction to samples loaded into diamond anvil cells we perform a comparative investigation of these HEA alloys in Ne and H2 pressure-transmitting media. Surprisingly, even under stresses far exceeding conventional industrial processes both Cantor and PGM alloys show exceptional resistance to hydride formation, on par with widely used industrial grade CuBe alloys. Our observations inspire optimism for practical HEA applications in hydrogen-relevant industry and technology e.g. coatings, etc, particularly those related to transport and storage.

cond-mat.mtrl-sci↗

arXiv2024

The high-pressure phase diagram of BaNi$_2$As$_2$: unconventional charge-density-waves and structural phase transitions

Structural phase transitions accompanied by incommensurate and commensurate charge density wave (CDW) modulations of unconventional nature have been reported in BaNi$_2$As$_2$, a nonmagnetic cousin of the parent compound of Fe-based superconductors, BaFe$_2$As$_2$. The strong dependence of the structural and CDW transitions of BaNi$_2$As$_2$ on isoelectronic substitutions alongside original dynamical lattice effects suggests strong tunability of the electronic phase of the system through structural effects. Here, we present a comprehensive synchrotron x-ray diffraction and first-principles calculation study of the evolution of the crystal structure and lattice instabilities of BaNi$_2$As$_2$ as a function of temperature and hydrostatic pressure (up to 12 GPa). We report a cascade of pressure-induced structural phase transitions and electronic instabilities up to 10 GPa, above which all CDW superstructures disappear. We reveal that the stable high-pressure phase consists of planar Ni zigzag chains, from which the surrounding As atoms have been pushed away. This yields a strong reduction of the interlayer As-As distance (along the original c axis), akin to what is observed in the collapsed tetragonal structure of other pnictides, albeit here with a monoclinic structure. The discovery of polymorphs in the pressure-temperature phase diagram of BaNi$_2$As$_2$ emphasizes the importance of the relative Ni-Ni and Ni-As bond lengths in controlling the electronic ground state of this compound and increases our understanding of viable electronic phases under extreme conditions.

cond-mat.supr-con↗

arXiv2023

Polytypism of Incommensurately Modulated Structures of Crystalline Bromine upon Molecular Dissociation under High Pressure

Polytypism of incommensurately modulated structures was hitherto unobserved. Here, we found the phenomenon in simple halogen systems of bromine and iodine upon molecular dissociation in the solids under pressure. Single-crystal synchrotron X-ray diffraction in laser heated diamond anvil cells pressurised up to 112 GPa revealed a number of allotropes of bromine and iodine including polytypes of Br-IIIγ (Fmmm(00γ)s00) with γ varying within 0.18 to 0.3.

cond-mat.mtrl-sci↗

arXiv2023

Isostructural phase transition in Tb2Ti2O7 under pressure and temperature: Insights from synchrotron X-ray diffraction

Tb2Ti2O7, a pyrochlore system, has garnered significant interest due to its intriguing structural and physical properties and their dependence on external physical parameters. In this study, utilizing high-brilliance synchrotron X-ray diffraction, we conducted a comprehensive investigation of structural evolution of Tb2Ti2O7 under external pressure and temperature. We have conclusively confirmed the occurrence of an isostructural phase transition beyond the pressure of 10 GPa. The transition exhibits a distinct signature in the variation of lattice parameters under pressure and leads to changes in mechanical properties. The underlying physics driving this transition can be understood in terms of localized rearrangement of atoms while retaining the overall cubic symmetry of the crystal. Notably, the observed transition remains almost independent of temperature. Our findings provide insights into the distinctive behaviour of the isostructural phase transition in Tb2Ti2O7.

cond-mat.mtrl-sci↗

arXiv2022

High-Pressure Synthesis of Seven Lanthanum Hydrides with a Significant Variability of Hydrogen Content

The lanthanum-hydrogen system has attracted significant attention following the report of superconductivity in LaH10 at near-ambient temperatures and high pressures. Here, we present the results of our single-crystal X-ray diffraction studies on this system, supported by density functional theory calculations, which reveal an unexpected chemical and structural diversity of lanthanum hydrides synthesized in the range of 50 to 180 GPa. Seven lanthanum hydrides were produced, LaH3, LaH~4, LaH4+δ, La4H23, LaH6+δ, LaH9+δ, and LaH10+δ, and the atomic coordinates of lanthanum in their structures determined. The regularities in rare-earth element hydrides unveiled here provide clues to guide the search for other synthesizable hydrides and candidate high-temperature superconductors. The hydrogen content variability in lanthanum hydrides and the samples' phase heterogeneity underline the challenges related to assessing potentially superconducting phase(s) and the nature of electronic transitions in high-pressure hydrides.

cond-mat.mtrl-sci↗

arXiv2022

Magnetism in four-layered Aurivillius Bi$_5$FeTi$_3$O$_{15}$ at high pressures : A nuclear forward scattering study

We report the structural and magnetic properties of four-layer Aurivillius compound Bi$_5$FeTi$_3$O$_{15}$ (BFTO) at high hydrostatic pressure conditions. The high-pressure XRD data does not explicitly show structural phase transitions with hydrostatic pressure, however the observed changes in lattice parameters indicate structural modifications at different pressure values. In the initial pressure region values, the lattice parameters $\textit{a}$- and $\textit{b}$- are nearly equal implying a quasi-tetragonal structure, however as the pressure increases $\textit{a}$- and $\textit{b}$- diverges apart and exhibits complete orthorhombic phase at pressure values of about $\geq$8 GPa. Principal component analysis of high pressure Raman measurements point out an evident change in the local structure at about 5.5 GPa indicating that the evolution of the local structure under applied pressure seems to not follow crystallographic changes (long range order). Nuclear forward scattering (NFS) measurement reveal the development of magnetic ordering in BFTO at 5K with high pressures. A progressive increase in magnetic order is observed with increase in pressure at 5K. Further, NFS measurements carried out at constant pressure (6.4GPa) and different temperatures indicate that the developed magnetism disappears at higher temperatures (20K). It is attempted to explain these observations in terms of the observed structural parameter variation with pressure.

cond-mat.mtrl-sci↗

arXiv2021

Aromatic Hexazine [N6]4- Anion Revealed in the Complex Structure of the High-Pressure Potassium Nitride K9N56

Recent high-pressure synthesis of pentazolates and subsequent stabilization of the aromatic [N5]- anion at atmospheric pressure had an immense impact on nitrogen chemistry. Here, we present the first synthesis of an aromatic hexazine [N6]4- anion realized in high-pressure potassium nitride K9N56 at 46 and 61 GPa. The extremely complex structure of K9N56 was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. This result resolves a long-standing question of the aromatic hexazine stability and the possibility of its synthesis.

cond-mat.mtrl-sci↗

arXiv2021

Structure and vibrational properties of methane up to 71 GPa

Single-crystal synchrotron X-ray diffraction, Raman spectroscopy, and first principles calculations have been used to identify the structure of the high-pressure (HP) phase of molecular methane above 20 GPa up to 71 GPa. The structure of HP phase is trigonal R3, which can be represented as a distortion of the cubic phase B, previously documented at 7-15 GPa and confirmed here. The positions of hydrogen atoms in HP phase have been 19 obtained from first principles calculations. The molecules occupy four different crystallographic sites in phases B and eleven sites in the HP phase, which result in splitting of molecular stretching modes detected in Raman spectroscopy and assigned here based on 22 a good agreement with the Raman spectra calculated from the first principles.

cond-mat.mtrl-sci↗