Hydrostatic pressure-induced transformations and multifunctional properties of Francium-based halide perovskite FrCaCl3: Insights from first-principles calculations.

Under varying hydrostatic pressures ranging from 0 to 150 GPa, first-principles calculations were conducted to investigate the structural, electronic, bonding, optical, elastic, and mechanical characteristics of the Lead (Pb)-free halide perovskite FrCaCl3 using both the GGA and hybrid HSE06 parameterized density functional theory (DFT). Since the FrCaCl3 cubic perovskite has not yet been synthesized experimentally, its structural and thermodynamic stabilities are confirmed by the Goldschmidt tolerance factor, the octahedral factor, and the formation energy. The induction of pressure has caused a simultaneous decrease in both the lattice parameters and the electronic band gap. Applying the hybrid HSE06 potential refines the accuracy of the band gap, with values decreasing from 5.705 to 2.618 eV from 0 to 150 GPa pressure, suggesting improved optoelectronic attributes. Employing pressure facilitates the formation of stronger chemical bonds characterized by reduced bond lengths. The investigation of optical functions demonstrates that with increased pressure ranging to 150 GPa, the optical conductivity along with the absorption coefficient is oriented towards the low-energy region. The FrCaCl3 perovskite has the prospect to be used in X-ray imaging and other fields of nuclear medicine and diagnostics as it contains the radioactive element Francium (Fr). Additionally, it is found via the study of mechanical characteristics that FrCaCl3 is mechanically stable under various applied pressure, and adding pressure makes it more ductile as well as more anisotropic.

Amorphous-like thermal conductivity and high mechanical stability of cyclopentane clathrate hydrate.

The thermal conductivity κ of cyclopentane clathrate hydrate (CP CH) of type II was measured at temperatures down to 100 K and at pressures up to 1.3 GPa. The results show that CP CH displays amorphous-like κ characteristic of many crystalline clathrate hydrates, e.g., tetrahydrofuran (THF) CH. The magnitude of κ is 0.47 W m-1 K-1 near the melting point of 280 K at atmospheric pressure, and it is almost independent of pressure and temperature T: ln κ = -0.621-40.1/T at atmospheric pressure (in SI-units). This is slightly less than κ of type II CHs of water-miscible solvents such as THF. Intriguingly, unlike other water-rich type II clathrate hydrates of water-miscible molecules M (M·17 H2O), CP CH does not amorphize at pressures up to 1.3 GPa at 130 K and also remains stable up to 0.5 GPa at 240 K. This shows that CP CH is mechanically more stable than the previously studied water-rich type II CHs, and suggests that repulsive forces between CP and the H2O cages increase the mechanical stability of crystalline CP CH. Moreover, we show that κ of an ice-CH mixture, which often arises for CHs that form naturally, is described by the average of the parallel and series heat conduction models to within 5% for ice contents up to 22 wt%. The findings provide a better understanding of the thermal and stability properties of clathrate hydrates for their applications such as gas storage compounds.

Pressure-driven modification of optoelectronic features of ACaCl3 (A = Cs, Tl) for device applications.

Intending to advance the use of halide-perovskites in technological applications, in this research, we investigate the structural, electronic, optical, and mechanical behavior of metal-halide perovskites ACaCl3 (A = Cs, Tl) through first-principle analysis and assess their potential applications. Due to the applied hydrostatic pressure, the interaction between constituent atoms increases, thereby causing the lattice parameter to decrease. The band structure reveals that band gap nature transits from indirect to direct at elevated pressure. Moreover, at high pressure, the electronic band structure shows a notable band gap contraction from the insulator (>5.0 eV) to the semiconductor region, which makes them promising for electronic applications. The charge density map explores the ionic and covalent characteristics of Cs/Tl-Cl and Ca-Cl under pressured and unpressurized environments. Induced pressure enhances the optical conductivity as well as the optical absorption that moves toward the low-energy region (red shift), making ACaCl3 (A = Cs, Tl) advantageous for optoelectronic applications. Additionally, this study reveals that the mechanical properties of ductility and anisotropy were found to be improved at higher pressures than in ambient conditions. Overall, this study will shed light on the technological applications of lead-free halide perovskites in extreme pressure conditions.

Draft genome sequencing of a multidrug-resistant Salmonella enterica subspecies enterica serovar Typhimurium strain isolated from chicken in Bangladesh.

Herein this study, we sequenced the genome of a multidrug-resistant Salmonella enterica serovar Typhimurium strain MBR-MFRK-23 isolated from the liver tissue of a diseased layer chicken. The 4,964,854-bp draft genome comprises 50 contigs with 50.5× coverage and 52.1% GC content and is typed as S. enterica sequence type 19.

Tuning band gap and enhancing optical functions of AGeF3 (A = K, Rb) under pressure for improved optoelectronic applications.

The current study diligently analyzes the physical characteristics of halide perovskites AGeF3 (A = K, Rb) under hydrostatic pressure using density functional theory. The goal of this research is to reduce the electronic band gap of AGeF3 (A = K, Rb) under pressure in order to improve the optical characteristics and assess the compounds' suitability for optoelectronic applications. The structural parameters exhibit a high degree of precision, which correlates well with previously published work. In addition, the bond length and lattice parameters decrease significantly leading to a stronger interaction between atoms. The bonding between K(Rb)-F and Ge-F reveal ionic and covalent nature, respectively, and the bonds become stronger under pressure. The application of hydrostatic pressure demonstrates remarkable changes in the optical absorption and conductivity. The band gap becomes lower with the increment of pressure, resulting in better conductivity. The optical functions also predict that the studied materials might be used in a variety of optoelectronic devices operating in the visible and ultraviolet spectrum. Interestingly, the compounds become more suitable to be used in optoelectronic applications under pressure. Moreover, the external pressure has profound dominance on the mechanical behavior of the titled perovskites, which make them more ductile and anisotropic.

Hydrothermal Synthesis and Crystal Structure of a Novel Bismuth Oxide: (K0.2Sr0.8)(Na0.01Ca0.25Bi0.74)O3.

A novel distorted perovskite-type (K0.2Sr0.8)(Na0.01Ca0.25Bi0.74)O3 was prepared by a hydrothermal method using the starting materials NaBiO3·nH2O, Sr(OH)2·8H2O, Ca(OH)2, and KOH. Single-crystal X-ray diffraction of the novel compound revealed a GdFeO3-related structure belonging to the monoclinic system of the space group Cc with the following cell parameters: a = 11.8927 (17) Å, b = 11.8962 (15) Å, c = 8.4002 (10) Å, and ß = 90.116 (9)°. The final R-factors were obtained as R 1 = 0.0354 and wR 2 = 0.0880 (using all the data). K+ and Sr2+ ions were distributed at four types of A-sites. On the other hand, four Bi5+-sites (Bi1, Bi2, Bi3, and Bi4) were occupied by four Ca2+ ions (Ca1, Ca2, Ca3, and Ca4), and the first three B-sites were occupied predominantly by Bi5+ with Na+ ions. The forth B-site was occupied predominantly by the Ca2+ ion with Bi5+ ions. Two types of B-sites, thus forming tilted distorted (Na/Ca/Bi)O6 and (Bi/Ca)O6 octahedra, have an ordering of 3:1 represented as (K/Sr)4(Na/Ca/Bi)3(Bi/Ca)O12. The distorted (Na/Ca/Bi)O6 and (Ca/Bi)O6 octahedra formed a perovskite-type network by corner sharing with features closely matching those of a GdFeO3-type structure. The novel compound is the first example of a perovskite-type bismuth oxide containing only Bi5+ in a system without a Ba atom and has a unique ordering (3:1) of the B site. The compound showed photocatalytic activity for phenol degradation under visible light irradiation.

Ultra-violet to visible band gap engineering of cubic halide KCaCl3 perovskite under pressure for optoelectronic applications: insights from DFT.

Density functional theory is utilized to explore the effects of hydrostatic pressure on the structural, electrical, optical, and mechanical properties of cubic halide perovskite KCaCl3 throughout this study. The interatomic distance is decreased due to the pressure effect, which dramatically lowers the lattice constant and unit cell volume of this perovskite. Under pressure, the electronic band gap shrinks from the ultra-violet to visible region, making it easier to move electrons from the valence band to the conduction band, which improves optoelectronic device efficiency. Furthermore, the band gap nature is switched from indirect to direct around 40 GPa pressure, which is more suitable for a material to be exploited in optoelectronic applications. The use of KCaCl3 in microelectronics, integrated circuits, QLED, OLED, solar cells, waveguides, solar heat reduction materials, and surgical instruments has been suggested through deep optical analysis. The use of external hydrostatic pressure has a considerable impact on the mechanical properties of this material, making it more ductile and anisotropic.

Hydrothermal Synthesis and Crystal Structure of a Mixed-Valence Bismuthate, Na3Bi3O8.

Four types of bismuth oxides, Na3Bi3O8, NaBiO3, α-Bi2O3, and ε-Bi2O3, were obtained by hydrothermal reactions using NaBiO3·nH2O in NaOH solution. The crystal structure of a new phase (Na3 Bi3+)Bi25+O8 ((Na0.75Bi0.25)2BiO4) was determined by using single crystal X-ray diffraction data, and this compound was found to show a Na2MnCl4-related structure with a monoclinic system (space group, Pm) with the following lattice parameters: a = 5.990 (2) Å, b = 3.335 (2) Å, c = 10.108 (2) Å, and ß = 91.08 (3)°. The final R-factors R1 and wR2 were 0.041 and 0.090 (all data), respectively. The new phase was composed of mixed valence states of Bi (Bi3+ and Bi5+, with a mean Bi valence of 4.30) with five distinct Bi sites, where two Bi5+ (Bi1 and Bi2) fully occupied the distorted octahedral sites and three Bi3+ (Bi3, Bi4, and Bi5) were statistically distributed at the split sites with Na+ (Na3, Na4, and Na5). The Na6 site is fully occupied. The distorted Bi5+O6 octahedra formed one-dimensional chains via edge-sharing along the b-axis, with the chains held by Bi3+/Na+ split sites. The structural feature except for the split distribution of Bi3+/Na+ was classified as a Na2MnCl4-type structure. DFT calculations based on a model discounting the split distribution of Bi3+/Na+ indicated that Bi 6s and O 2p orbitals form sp hybridization at the conduction band. This new mixed valence bismuth oxide exhibited photocatalytic activity for phenol degradation under visible light irradiation. In addition to Na3Bi3O8, the hydrothermal reaction using NaBiO3·nH2O in NaOH solution yielded micrometer-sized single crystals of an ilmenite-type NaBiO3 and two polymorphs of bismuth oxides with monoclinic (α-Bi2O3) and orthorhombic (ε-Bi2O3) structures, depending on the reaction temperature and NaOH concentration.

Hydrothermal Synthesis and Crystal Structure of a (Ba0.54K0.46)4Bi4O12 Double-Perovskite Superconductor with Onset of the Transition Tc ∼ 30 K.

A new superconducting double perovskite was successfully synthesized by a low-temperature hydrothermal reaction at 240 °C. The crystal structure refinement of this double perovskite was done by single-crystal X-ray diffraction, and it had a cubic unit cell of a = 8.5207(2) Å with space group Im3̅m (No. 229). This superconducting double-perovskite chemical composition was estimated by electron probe microanalysis and was similar to the refined data. The superconducting transition temperature of the double perovskite was ∼30 K; the electrical resistivity began to fall at ∼25 K, and zero resistivity occurred below 7 K. Moreover, temperature-dependent resistivity under various magnetic fields and isothermal magnetization measurements ensured the nature of a type II superconductor for the sample. Finally, the metallic nature of the material was investigated by a first-principles study.

Hydrothermal Synthesis of Pyrochlore-Type Pentavalent Bismuthates Ca2Bi2O7 and Sr2Bi2O7.

The pyrochlore-type Ca2Bi2O7 and Sr2Bi2O7 have been synthesized from a low-temperature hydrothermal route using NaBiO3·nH2O as a starting material. The crystal structures of these compounds were refined using synchrotron powder X-ray diffraction data. The cell parameters were found to be a = 10.75021 (5) Å and 10.94132 (6) Å for Ca2Bi2O7 and Sr2Bi2O7, respectively. Density functional theory calculations showed the metallic band structure, but the negligible mixing of O2 2p bands with the A-site alkaline-earth-metal states and weak overlap with the conduction bands result in the semiconducting behavior.

Crystal Structure, Thermal Behavior, and Photocatalytic Activity of NaBiO3· nH2O.

The crystal structure of NaBiO3· nH2O was refined using synchrotron powder X-ray diffraction and was assigned to a trigonal unit cell (space group P3̅) consisting of layered structures formed by edge-sharing BiO6 octahedra and consisting of an interlayer composed of water molecules sandwiched between two layers of sodium atoms, perpendicular to the c axis. An intermediate phase was observed during the dehydration of the hydrated compound. Density of state calculations showed hybridization of the Bi 6s and O 2p orbitals at the bottom of the conduction bands for both the hydrated and the dehydrated phases, which narrows the band gap and promotes their photocatalytic activity in the visible region.