Crystals

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9 pages, 2347 KB

Open AccessArticle

Enhanced Thermal Stability in Cu1234 Superconductor with Oxygen Annealing

by Luchuan Shi, Kai Huang, Haoyu Zheng, Xiaoming Chen, Yuling Dai, Yi Peng, Jianfa Zhao, Xiancheng Wang and Changqing Jin

Crystals 2026, 16(4), 261; https://doi.org/10.3390/cryst16040261 - 13 Apr 2026

Viewed by 393

Abstract

Recently, CuBa₂Ca₃Cu₄O_10+δ (Cu1234) has garnered significant interest owing to its distinctive triple-high superconducting properties (118K high T_c, combined with high J_c and high H_irr at liquid nitrogen temperature at ambient pressure) and [...] Read more.

Recently, CuBa₂Ca₃Cu₄O_10+δ (Cu1234) has garnered significant interest owing to its distinctive triple-high superconducting properties (118K high T_c, combined with high J_c and high H_irr at liquid nitrogen temperature at ambient pressure) and potential for practical applications. The Cu1234 is initially synthesized at high pressures and is stable at a room temperature range but tends to decompose upon heating above 300 °C at ambient. In this study, we investigate the thermal stability of Cu1234 through annealing at various temperatures and oxygen pressures. It is found that Cu1234 starts to decompose at approximately 350 °C, 550 °C, and 600 °C when annealed at 1 bar, 100 bar, and 150 bar oxygen pressure, respectively. Prior to decomposition, however, the superconducting properties remain largely unchanged. The decrease in oxygen occupancy within the BaO layer of the BaCuO_3−δ charge reservoir block is proposed to be the primary cause of the structural instability of Cu1234, while higher oxygen pressures retard oxygen loss from this block. Our result suggests that the decomposition temperature of Cu1234 will further increase with higher oxygen pressure, e.g., possibly to 800 °C at 260 bar if a linear extrapolation is adopted. This study offers important insights for fabricating Cu1234 tapes via the powder-in-tube method. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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15 pages, 3100 KB

Open AccessArticle

Crystal Structure and Temperature-Induced Phase Transitions in the New Copper Vanadate Cs₂Cu₂[V₄O₁₂]Br₂

by Ilya V. Kornyakov, Vladimir N. Bocharov and Sergey V. Krivovichev

Crystals 2026, 16(4), 252; https://doi.org/10.3390/cryst16040252 - 10 Apr 2026

Viewed by 427

Abstract

The new compound Cs₂Cu₂[V₄O₁₂]Br₂ was synthesized by the chemical vapor transport reaction method. Structural data obtained by single-crystal X-ray diffraction in the temperature range 100–700 K revealed three successive (with decreasing temperature) structural phase [...] Read more.

The new compound Cs₂Cu₂[V₄O₁₂]Br₂ was synthesized by the chemical vapor transport reaction method. Structural data obtained by single-crystal X-ray diffraction in the temperature range 100–700 K revealed three successive (with decreasing temperature) structural phase transitions: from the high-temperature aristotype structure I4/mmm (>550 K) to the polymorph P4/mnc (550–340 K), then to P4/m (340–300 K), and finally to the low-temperature phase I4/m (<300 K). The crystal structure of the new compound is based upon the Cu₂[V₄O₁₂]⁰ layers, consisting of four-membered rings of corner-sharing vanadate tetrahedra linked by CuO₄ squares. Analysis of the structural evolution with increasing temperature shows that the entire sequence of phase transitions is governed by the rotation of the [V₄O₁₂]⁴⁻ rings about the z axis. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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19 pages, 3309 KB

Open AccessArticle

Synthesis, Anion Disordering and Electronic Structure of Rb₂KWO₃F₃ Elpasolite

by Victor Atuchin, Tatyana Gavrilova, Ludmila Isaenko, Valery Kesler, Maxim Molokeev, Aleksandr Oreshonkov and Sergey Zhurkov

Crystals 2026, 16(1), 18; https://doi.org/10.3390/cryst16010018 - 26 Dec 2025

Viewed by 876

Abstract

Rb₂KWO₃F₃ elpasolite was synthesized via the solid-state reaction route. The phase purity of the obtained sample was verified by the XRD analysis with Rietveld refinement in space group Fm-3m, yielding the unit cell parameter a [...] Read more.

Rb₂KWO₃F₃ elpasolite was synthesized via the solid-state reaction route. The phase purity of the obtained sample was verified by the XRD analysis with Rietveld refinement in space group Fm-3m, yielding the unit cell parameter a = 8.92413 (17) Å. The electronic structure and chemical states of the constituent elements were investigated using X-ray photoelectron spectroscopy. The binding energy of the W 4f_7/2 core level (34.95 eV) was found to be characteristic of the W⁶⁺ oxidation state, while the values for Rb 3d, K 2p, O 1s and F 1s levels were consistent with those reported for related oxide and oxyfluoride compounds. First-principles density functional theory calculations were performed to model the electronic structure. The fac-configuration of the WO₃F₃ octahedra was identified as the most energetically favorable. The calculations revealed a direct band gap of 4.38 eV, with the valence band maximum composed primarily of O 2p orbitals and the conduction band minimum formed by W 5d orbitals. This combined experimental/theoretical study shows that the electronic structure and wide bandgap of Rb₂KWO₃F₃ are governed by the WO₃F₃ units and are largely insensitive to the Rb/K substitution. The wide bandgap identifies this class of oxyfluorides as a promising platform for developing new UV-transparent materials. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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14 pages, 3483 KB

Open AccessArticle

The Influence of Annealing on the Structural, Optical and Electrical Properties of Copper Selenite Nanocrystals Synthesized by the Chemical Deposition Method

by Gulnaz Sarsekhan, Abay Usseinov, Aiman Akylbekova, Abdirash Akilbekov, Alma Dauletbekova, Diana Junisbekova, Ainash Abdrakhmetova, Gulnara Aralbayeva, Leila Kassenova and Zein Baimukhanov

Crystals 2025, 15(12), 1060; https://doi.org/10.3390/cryst15121060 - 14 Dec 2025

Viewed by 628

Abstract

This work presents a study of copper selenite nanocrystals, obtained for the first time by chemical deposition (template synthesis) in a SiO₂/Si track template, and investigates their properties. The obtained nanostructures were subjected to structural, optical, and electrical analysis. After deposition, [...] Read more.

This work presents a study of copper selenite nanocrystals, obtained for the first time by chemical deposition (template synthesis) in a SiO₂/Si track template, and investigates their properties. The obtained nanostructures were subjected to structural, optical, and electrical analysis. After deposition, X-ray diffraction (XRD) analysis confirmed the formation of the orthorhombic phase CuSeO₃. Subsequent annealing in a vacuum at 800 °C and 1000 °C led to successive phase transformations: to the monoclinic phase and, finally, to the triclinic polymorph of copper selenite. Photoluminescence (PL) analysis showed that the intensity and spectral position of the emission peaks vary depending on the crystal structure, which is associated with changes in defects and bandgap width as a result of heat treatment. Current–voltage characteristic (CVC) measurements showed that the phase composition significantly affects electrical conductivity. In particular, the transition to the triclinic phase after annealing at 1000 °C led to noticeable changes in optical and electrical properties compared to the initial material. Thus, a direct relationship has been established between heat treatment conditions, crystal structure, and functional properties of CuSeO₃-based materials, opening up possibilities for their application in photonics and electronics. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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12 pages, 5377 KB

Open AccessArticle

Influence of Defects-Induced Stresses on Birefringence in SrTiO₃ Single Crystals

by Iwona Lazar, Krzysztof Szot and Krystian Roleder

Crystals 2023, 13(7), 985; https://doi.org/10.3390/cryst13070985 - 21 Jun 2023

Cited by 4 | Viewed by 1955

Abstract

Significant applications of SrTiO₃ single crystals in electronics require knowledge about the influence of structural imperfections on their optical properties. Birefringence temperature changes were investigated in a few SrTiO₃ single crystals in a broad temperature range, from 85 K to 250 [...] Read more.

Significant applications of SrTiO₃ single crystals in electronics require knowledge about the influence of structural imperfections on their optical properties. Birefringence temperature changes were investigated in a few SrTiO₃ single crystals in a broad temperature range, from 85 K to 250 K. The birefringence was found to be a non-linear function below the transition Ts at 105 K, and non-linear changes in the optical indicatrix orientation accompanied it. A weak residual birefringence was permanently present a dozen degrees above the phase transition temperature Ts. This is mainly connected with dislocations, which induce local stresses and shift transition points even up to about 200 K. The essential role of imperfections on optical properties was studied in a SrTiO₃ 24° bi-crystal reduced at 1000 K and under low oxygen pressure. In such an intentionally defected crystal, an increase of non-linearities in Δn(T) dependence was observed below and above the transition point Ts. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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11 pages, 5235 KB

Open AccessArticle

Electrostimulation and Nanomanipulation of Two-Dimensional MoO_3-x Layers Grown on Graphite

by Aleksandra Nadolska, Dorota A. Kowalczyk, Iaroslav Lutsyk, Michał Piskorski, Paweł Krukowski, Paweł Dąbrowski, Maxime Le Ster, Witold Kozłowski, Rafał Dunal, Przemysław Przybysz, Wojciech Ryś, Klaudia Toczek, Paweł J. Kowalczyk and Maciej Rogala

Crystals 2023, 13(6), 905; https://doi.org/10.3390/cryst13060905 - 1 Jun 2023

Cited by 7 | Viewed by 2922

Abstract

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical [...] Read more.

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO_3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO₃ monolayer. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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14 pages, 4498 KB

Open AccessArticle

Theoretical Study on (n,n)-Nanotubes Rolled-up from B/N Substituted Me-Graphene

by Hong-Chao Luo, Feng-Yin Li, Ya-Nan Zhang, Hong-Xing Zhang, Roberts I. Eglitis and Ran Jia

Crystals 2023, 13(5), 829; https://doi.org/10.3390/cryst13050829 - 17 May 2023

Cited by 2 | Viewed by 2419

Abstract

In this work, the

(n, n)

-type nanotube systems rolled up from the B/N substituted Me-graphene (i.e., Me-CBNT and Me-CNN, respectively) were investigated with the aid of the density functional theory (DFT). Due to the lattice dynamic instabilities until

n = 10

[...] Read more.

In this work, the

(n, n)

-type nanotube systems rolled up from the B/N substituted Me-graphene (i.e., Me-CBNT and Me-CNN, respectively) were investigated with the aid of the density functional theory (DFT). Due to the lattice dynamic instabilities until

n = 10

, the

(n, 0)

and

(n, m)

nanotube systems were not involved in this study. According to our calculations at the Perdew-Burke-Ernzerhof (PBE) level, the

(n, n)

Me-CBNT and Me-CNNT systems possess excellent mechanical strengths. The Young’s moduli of Me-CBNTs can reach 60% of single-walled carbon nanotubes (SWCNTs), while their mass densities are only around 70% of SWCNTs. Based on the fully relaxed geometric configurations at the PBE level, the electronic configurations of the related nanotubes were evaluated by using the global hybrid functional B3LYP with 36% Fock exchanges. The

(n, n)

Me-CBNTs are metallic, while the

(n, n)

Me-CNNTs are semiconductors with the inherent band gaps in the range of 3.08 eV to 3.31 eV. The Bloch flat bands appear on both sides of their Fermi levels, indicating the localized charge carriers. Their band edge arrangements imply that these materials are promising candidates for the photocatalytic water splitting reactions at certain pH values. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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Review

Jump to: Research

17 pages, 7035 KB

Open AccessReview

The Effect of Reduction and Oxidation Processes on the Work Function of Metal Oxide Crystals: TiO₂(110) and SrTiO₃(001) Case

by Karol Cieślik, Dominik Wrana, Maciej Rogala, Christian Rodenbücher, Krzysztof Szot and Franciszek Krok

Crystals 2023, 13(7), 1052; https://doi.org/10.3390/cryst13071052 - 3 Jul 2023

Cited by 12 | Viewed by 4504

Abstract

The strict control of the work function of transition metal oxide crystals is of the utmost importance not only to fundamental research but also to applications based on these materials. Transition metal oxides are highly abundant in electronic devices, as their properties can [...] Read more.

The strict control of the work function of transition metal oxide crystals is of the utmost importance not only to fundamental research but also to applications based on these materials. Transition metal oxides are highly abundant in electronic devices, as their properties can be easily modified using redox processes. However, this ease of tuning is a double-edged sword. With the ease of manipulation comes difficulty in controlling the corresponding process. In this study, we demonstrate how redox processes can be induced in a laboratory setting and how they affect the work function of two model transition metal oxide crystals, namely titanium dioxide TiO₂(110) and strontium titanate SrTiO₃(001). To accomplish this task, we utilized Kelvin Probe Force Microscopy (KPFM) to monitor changes in work function, Scanning Tunneling Microscopy (STM), and Low-Energy Electron Diffraction (LEED) to check the surface morphology and reconstruction, and we also used X-ray Photoelectron Spectroscopy (XPS) to determine how the surface composition evolves. We also show that using redox processes, the work function of titanium dioxide can be modified in the range of 3.4–5.0 eV, and that of strontium titanate can be modified in the range of 2.9–4.5 eV. Moreover, we show that the presence of an oxygen-gaining material in the vicinity of a transition metal oxide during annealing can deepen the changes to its stoichiometry and therefore the work function. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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25 pages, 6361 KB

Open AccessReview

Review of First Principles Simulations of STO/BTO, STO/PTO, and SZO/PZO (001) Heterostructures

by Roberts I. Eglitis, Dmitry Bocharov, Sergey Piskunov and Ran Jia

Crystals 2023, 13(5), 799; https://doi.org/10.3390/cryst13050799 - 10 May 2023

Cited by 26 | Viewed by 6782

Abstract

In this study, we review our first-principles simulations for STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures. Specifically, we report ab initio B3PW calculations for STO/BTO, STO/PTO, and SZO/PZO (001) interfaces, considering non-stoichiometric heterostructures in the process. Our ab initio B3PW calculations demonstrate that charge [...] Read more.

In this study, we review our first-principles simulations for STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures. Specifically, we report ab initio B3PW calculations for STO/BTO, STO/PTO, and SZO/PZO (001) interfaces, considering non-stoichiometric heterostructures in the process. Our ab initio B3PW calculations demonstrate that charge redistribution in the (001) interface region only subtly affects electronic structures. However, changes in stoichiometry result in significant shifts in band edges. The computed band gaps for the STO/BTO, STO/PTO, and SZO/PZO (001) interfaces are primarily determined according to whether the topmost layer of the augmented (001) film has an AO or BO₂ termination. We predict an increase in the covalency of B-O bonds near the STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures as compared to the BTO, PTO, and PZO bulk materials. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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