Ba Atoms Research Articles

Phase transformations in barium-strontium niobate SBN-50 in the temperature range from 80 K to 700 K according to Raman spectroscopy data

The lattice dynamics of the Sr0.5Ba0.5Nb2O6 (SBN-50) ceramic was studied using Raman spectroscopy in the temperature range of 80-700 K with a step of 10 K. The analysis of the Raman spectra in the range ν=50-1000 cm-1 revealed features in the temperature dependence behavior of the optical modes frequencies associated with the displacement of Ba, Sr and Nb atoms from their average positions in the crystal lattice, which is associated with a macroscopic phase transition from the paraelectric to the ferroelectric phase in the vicinity of 390 K. It is shown that anomalies at T~565 K on the temperature dependences of the frequency and line half-width corresponding to the oscillations of the NbO6 octahedron can be caused by the presence of polar nanoregions in the paraelectric phase in SBN-50. When the sample was cooled to a temperature of 80 K, the behavior was recorded in the Raman spectra, indicating the occurrence of a structural phase transition in the ferroelectric phase in the vicinity of 190 K. The reasons for the revealed patterns are discussed. Keywords: ferroelectric, Raman scattering, SBN, tetragonal tungsten bronze.

Zn/Al-centered tetrahedral framework oxide Ba4Zn2Al2O9

Single crystals of Ba4Zn2Al2O9 were obtained by heating a mixture of BaCO3, ZnO, and Al2O3 at 1413 ​K in a dry air atmosphere. X-ray crystal structure analysis revealed that the compound crystalizes in a monoclinic cell (a ​= ​6.9444(2) Å, b ​= ​5.91650(10) Å, c ​= ​13.5842(3) Å, β ​= ​103.955(1)°) with the space group P21/n. The crystal structure can be characterized as a substitution of Zn/AlO4 tetrahedra for B-cation-centered O octahedra of a perovskite-type structure (ABO3). The vacant spaces surrounded by planes of the tetrahedra with eight- and ten-fold coordinations of O atoms are occupied by Ba atoms. The melting temperature (1444 ​K), electrical conductivity (1.5 ​× ​10–6 ​S ​cm–1 at 1073 ​K), relative permittivity (24 ​at 298 ​K and 1 ​MHz), and linear thermal expansion coefficient (9.72 ​× ​10–6 ​K–1 ​at 298–873 ​K) of a polycrystalline bulk sample were measured.

Ba2B13O19(OH)5·5H2O: A promising nonlinear optical material with a unique 2[B13O19(OH)5]∞ two-dimensional layer

A case of hydrous borate with the formula of Ba2B13O19(OH)5·5H2O was synthesized by the traditional hydrothermal method. It crystallizes in the chiral P1 space group and has a unique two-dimensional 2[B13O19(OH)5]∞ layer that is constructed by the hydrogen involved [B13O22(OH)5] fundamental building blocks (FBBs). The Ba atoms and H2O molecules are filled in the three-dimensional pore constructed by the 2[B13O19(OH)5]∞ layer. Interestingly, Ba2B13O19(OH)5·5H2O is the first case of hydrous borates that has the above rare [B13O22(OH)5] FBB and 2[B13O19(OH)5]∞ layer, which enriching the structural chemistry of borate system. The diffuse reflection spectrum result shows that the ultraviolet (UV) cutoff edge of Ba2B13O19(OH)5·5H2O is below 200 nm. Its second harmonic generation (SHG) response is approximately 1.0 times that of potassium dihydrogen phosphate at the 1064 nm fundamental wavelength and it is also phase-matchable. Both results indicate that the title compound is a nonlinear optical crystal for UV spectral region. Theoretical simulation calculation shows that the occupied VE states are mainly contributed by the O-2p orbitals, and therefore [B13O22(OH)5] groups are the main sources of SHG effects.

Crystal structure, lattice vibrational characteristics, and dielectric properties of Ba(Mg1/2Mo1/2)O3 ceramics sintered at different temperatures

Double perovskite structured Ba(Mg1/2Mo1/2)O3 (BMM) ceramics were prepared by traditional solid sintering methods at different sintering temperatures (Ts=1250–1325 °C). X-ray diffraction (XRD) data proved a 1:1 ordered face-centered cubic lattice (Fm-3 m), and the ceramic sintered at 1300 °C obtained maximum relative density. The lattice vibration characteristics were identified by Raman spectroscopy and far-infrared reflection spectroscopy. Based on the far-infrared data, a four-parameter semi-quantum model (FPSQ) was applied to calculate the intrinsic properties of BMM ceramics, and the obtained results approximated the measured values. The Raman shift of the BMM F2g(B) mode (attributed to the centrosymmetric vibration of Ba atom) was shown to be negatively correlated with the corrected permittivity and Ba-O bond length. With increasing sintering temperature (Ts), the relative density is positively correlated with the quality factor (Q × f), and the change of Ba-O bond length leads to distortion of the oxygen octahedron, which is positively correlated with the dielectric constant. The sintered BMM ceramics obtained their best dielectric properties at 1300 °C (εr= 4.987, Q × f = 23,069 GHz, f = 11.16 GHz).

High-temperature ideal Weyl semimetal phase and Chern insulator phase in ferromagnetic BaEuNiOsO6 and its (111) (BaEuNiOsO6)/(BaTiO3)10 superlattice

Weyl semimetals (WSMs) have recently stimulated intensive interest because they exhibit fascinating physical properties and also promise exciting technological applications. So far, however, the few confirmed magnetic WSMs generally have a large number of Weyl points either located away from the Fermi level $({E}_{F})$ or shrouded by nontopological Fermi surface pockets. Based on first-principles density functional theory calculations, we establish cubic double perovskite ${\mathrm{BaEuNiOsO}}_{6}$ to be a high Curie temperature $({T}_{c})$ ferromagnetic (FM) WSM with magnetization along the [111] direction, just two pairs of Weyl points at the ${E}_{F}$ and ${T}_{c}=325$ K. The strong FM is attributed to the strong FM Ni $3d$-Eu $4f$-Os $5d$ coupling induced by the substitution of half of Ba atoms with Eu atoms in double perovskite ${\mathrm{Ba}}_{2}{\mathrm{NiOsO}}_{6}$. Moreover, the momentum separation of one Weyl point pair is large, thus giving rise to not only a long (001) surface Fermi arc but also large anomalous Hall conductivity. Intriguingly, as a unique physical result of bulk ${\mathrm{BaEuNiOsO}}_{6}$ being a FM WSM, the (111) ${\mathrm{BaEuNiOsO}}_{6}$ monolayer (ML) superlattice $({\mathrm{BaEuNiOsO}}_{6})/{({\mathrm{BaTiO}}_{3})}_{10}$ is found to be a high-temperature (${T}_{c}=210$ K) Chern insulator with a large band gap of $\ensuremath{\sim}90$ meV. Therefore, cubic double perovskite ${\mathrm{BaEuNiOsO}}_{6}$ will provide a superior high-temperature material platform for exploring fundamental physics of Weyl fermions, and its (111) ML superlattices will offer a high-temperature magnetic topological insulator for studying exotic quantum phenomena such as the quantum anomalous Hall effect.

Zinkgruvanite, Ba<sub>4</sub>Mn<sup>2+</sup><sub>4</sub>Fe<sup>3+</sup><sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>O<sub>2</sub>(OH)<sub>2</sub>, a new ericssonite-group mineral from the Zinkgruvan Zn-Pb-Ag-Cu deposit, Askersund, Örebro County, Sweden

Abstract. Zinkgruvanite, ideally Ba4Mn42+Fe23+(Si2O7)2(SO4)2O2(OH)2, is a new member of the ericssonite group, found in Ba-rich drill core samples from a sphalerite- and galena- and diopside-rich metatuffite succession from the Zinkgruvan mine, Örebro County, Sweden. Zinkgruvanite is associated with massive baryte, barytocalcite, diopside and minor witherite, cerchiaraite-Al, and sulfide minerals. It occurs as subhedral to euhedral flattened and elongated crystals up to 4 mm. It is almost black and semi-opaque with a dark-brown streak. The lustre is vitreous to sub-adamantine on crystal faces and resinous on fractures. The mineral is brittle with an uneven fracture. VHN100=539, and HMohs ≈ 4.5. In thin fragments, it is reddish-black, translucent and optically biaxial (+), 2Vz > 70∘. Pleochroism is strong and deep brown-red (E ⊥ {001} cleavage) to olive-pale-brown. Chemical point analyses by WDS-EPMA (wavelength-dispersive X-ray spectroscopy electron probe microanalyser) together with iron valencies determined from Mössbauer spectroscopy yielded the empirical formula (based on 26 O+OH+F+Cl anions): (Ba4.02Na0.03)Σ4.05(Mn1.79Fe1.562+Fe0.423+Mg0.14Ca0.10Ni0.01Zn0.01)Σ4.03(Fe1.743+Ti0.20Al0.06)Σ2.00Si4(S1.61Si0.32P0.07)Σ1.99O24(OH1.63Cl0.29F0.08)Σ2.00. The mineral is triclinic, in space group P1¯, with unit-cell parameters a=5.3982(1) Å, b=7.0237(1) Å, c=14.8108(4) Å, α= 98.256(2)∘, β= 93.379(2)∘, γ= 89.985(2)∘ and V= 554.75(2) Å3 for Z=1. The eight strongest X-ray powder diffraction lines are the following (d Å (I %; hkl)): 3.508 (70; 103), 2.980(70; 114‾), 2.814 (68; 12‾2), 2.777 (70; 121), 2.699 (714; 200), 2.680 (68; 201‾), 2.125 (100; 124, 204) and 2.107 (96; 2‾21). The crystal structure (R1=0.0379 for 3204 reflections) is an array of TS (titanium silicate) blocks alternating with intermediate blocks. The TS blocks consist of HOH sheets (H for heteropolyhedral and O for octahedral) parallel to (001). In the O sheet, the Mn2+-dominant MO(1,2,3) sites give ideally Mn42+ pfu (per formula unit). In the H sheet, the Fe3+-dominant MH sites and AP(1) sites give ideally Fe23+Ba2 pfu. In the intermediate block, SO4 oxyanions and 11 coordinated Ba atoms give ideally 2× SO4Ba pfu. Zinkgruvanite is related to ericssonite and ferroericssonite in having the same topology and type of linkage of layers in the TS block. Zinkgruvanite is also closely compositionally related to yoshimuraite, Ba4Mn4Ti2(Si2O7)2(PO4)2O2(OH)2, via the coupled heterovalent substitution 2 Ti4++ 2 (PO4)3-→2 Fe3++ 2 (SO4)2− but presents a different type of linkage. The new mineral probably formed during a late stage of regional metamorphism of a Ba-enriched, syngenetic protolith, involving locally generated oxidized fluids of high salinity.

Investigating the Chemical Ordering in Quaternary Clathrate Ba8AlxGa16-xGe30.

Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate Ba8AlxGa16–xGe30 by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6c site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates Ba8AlxGa16–xGe30 and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties.

Exploring the structural evolution and electronic properties of medium-sized barium doped magnesium clusters

Projects about alkaline-earth metals doped magnesium are hot issues constantly in cluster science, while research in terms of Mid-Sized Ba atoms doped magnesium cluster was unreported. We adopted the CALYPSO method coupled with DFT calculation to simplify the process of structure searching at the range of BanMgm0/– (n = 1,2; m = 10–15) cluster. We found the doped Ba atoms tend to occupy convex capped sites in each structure. Meanwhile, the six-atom triangular prism as a major structure constructed the great mass of isomers. Based on the result of the relative stability survey, we selected BaMg13– and Ba2Mg13– to conduct further investigations, according to a different numbers of doped Ba atoms. Analysis of the bonding character manifests that the Mg-p orbital takes up the highest proportion for both BaMg13– and Ba2Mg13– cluster at HOMO, LUMO position as well as the existence of strong covalent bonds between Mg-Mg atoms and Ba-Mg atoms.

Ba33Zn22Al8O67 with a Framework of ([O(Zn/Al)4]/Ba)(Zn/AlO4)4 Motifs.

Single crystals of a new oxide, Ba33Zn22Al8O67 (melting point = 1452 K), were grown in a melt-solidified sample prepared by heating a compact of a BaCO3, ZnO, and Al2O3 mixed powder in a dry airflow. Ba33Zn22Al8O67 can be handled in dry air, but it decomposes into carbonates, hydroxides, and hydrates in humid air. Single-crystal X-ray structure analysis clarified that Ba33Zn22Al8O67 crystallizes in a cubic cell (a = 16.3328 (3) Å, space group F23) having a three-dimensional Zn/AlO4 framework in which {([OZn4]/Ba)(Zn/AlO4)4} motifs are connected to each other by bridging Zn/AlO4 tetrahedra. A Ba atom or a [OZn4] cluster is statistically situated at the center of the motif with a probability of 0.5. Motifs of another type, {([O(Zn/Al)4])(Zn/AlO4)4}, are isolated from the Zn/AlO4 framework. These motifs, {([OZn4]/Ba)(Zn/AlO4)4} and {([O(Zn/Al)4])(Zn/AlO4)4}, are alternatingly arranged along the a axis like a checkered cube, and Ba atoms are situated between the motifs. A linear thermal expansion coefficient of 10.4 × 10–6 K–1 was measured in an Ar gas flow at 301–873 K for a sintered Ba33Zn22Al8O67 polycrystalline sample with a relative density of 73%. A relative permittivity of 31 and a temperature coefficient of 15 ppm K–1 at 301 K were obtained for another sintered sample (relative density = 70%) in a dry airflow. The electrical conductivity at 1073 K and the activation energy for conduction at 923–1073 K measured for the sintered samples in dry and wet airflows were 6.2 × 10–7 S cm–1 and 0.65 eV and 2.9 × 10–6 S cm–1 and 0.59 eV, respectively.

Investigation of Ba and Ti sites occupation effects on structural, optical and dielectric properties of sol gel processed Y-doped BaTiO3 ceramics

Incorporation of chemical elements into the A and/or B sites of the ABO3 perovskite structure generates disorder (topological disorder, oxygen vacancies, …) in this structure which gives rise to effects more or less important on its chemical and physical properties. In particular, the structure, microstructure and the dielectric properties are affected under the effect of doping. In this regard, we investigate the above mentioned effects on BaTiO3 (BT) compounds doped with different percentages of Y. Indeed, X-Ray Diffraction (XRD) and Raman analyses show that Yttrium (Y) may replace both Ba and Ti atoms, and noticeably reduces the grain size of the sintered samples in conformity with Scanning Electron Microscopy (SEM) images. We show that the generated disorder consecutive to incorporation of Yttrium is also evidenced by the values of Urbach energy. We obtain relatively high values of the permittivity under doping without relaxation effect of this parameter but with the presence of a weak diffuse character of the ferro-to-paraelectric transition. Moreover, we show that resonances may be induced in BT under doping with Yttrium, and that the Positive Temperature Coefficient of Resistivity (PTCR) is present in the undoped (BT) and Y-doped BT samples.

Geochemistry of barium ions associated with biogenic manganese oxide nanoparticles generated by a fungus strain: Implications for radium sequestration in uranium mill tailings

Biogenic Mn oxides are reactive and ubiquitous in many Earth surface environments, yet their role in radionuclide sequestration at U mill-tailings sites still require an improved understanding at the nano- and molecular-scales. This study concerns the uptake of Ba, utilized as a safe and chemically appropriate surrogate for radioactive Ra, by biogenic Mn oxides produced by a fungal species, Coprinopsis urticicola, isolated from the mine water of the Ningyo-toge U mine, Okayama, Japan. The biogenic Mn oxides were identified as birnessite nanocrystals <10 nm in width having many vacancy sites in the MnO6 octahedral layers. Ba2+ adsorption experiments using biogenic birnessite were conducted at pH 6.00 ± 0.02 with the initial Ba concentrations ranging from 10–8 to 10–3 mol/L. The apparent distribution coefficient, Kd, was calculated to be 103.8 L/g for biogenic birnessite, which is comparable to the apparent Kd of Ra in the mill tailings pond at Ningyo-toge. Both in adsorption and coprecipitation experiments, extended X-ray absorption fine edge structure analysis of Ba L3 edge revealed that the Ba atom forms an inner-sphere complex with O atoms of the MnO6 layer. A slightly greater coordination number for coprecipitated Ba may be attributed to the formation of BaO binding to the newly overlying MnO6 layer during coprecipitation. Static desorption experiments for 7 days reveal that the steady-state release rate of adsorbed Ba is ∼1.4 times faster than that of the coprecipitated Ba, when the Ba concentration in the initial loading solution was ∼10–8 mol/L, indicating that the release of intercalated (coprecipitation) Ba to solution is retarded. The present study demonstrates the importance of fungus-generated Mn oxides as an efficient absorber of Ba2+, and likely Ra2+, among soil compounds in U mill-tailings. This may be applicable to other contaminated sites due to the ubiquitous occurrence of fungi in the environment.

New layered quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases: Crystal growth and physical properties

We report two new quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases with a new structure type, which are fully characterized by single crystal X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These two phases crystallize in tetragonal cell with space group I4/mmm (#139) and Pearson symbol tI26. The refined lattice parameters are a = 4.164(1) Å, c = 24.088(3) Å for BaCu6Sn2As4−x, and a = 4.053(2) Å, c = 24.08(1) Å for BaCu6Sn2P4−x, respectively. They possess a distinct layered feature composed of Cu6Sn2Pnx (Pn = P, As) layers sandwiched by the Ba atoms. The Cu-Sn framework of the Cu6Sn2Pnx layer is closely related to the well-known Cu2Sb-type structure, and Pn atoms are found occupying two interstitial sites caused by close packing of Cu and Sn atoms or capped on the top of square nets formed by Cu atoms. The compounds are also characterized by electrical transport measurements down to 2 K.

Transport anomalies in the layered compound BaPt4Se6

We report a layered ternary selenide BaPt4Se6 featuring sesqui-selenide Pt2Se3 layers sandwiched by Ba atoms. The Pt2Se3 layers in this compound can be derived from the Dirac-semimetal PtSe2 phase with Se vacancies that form a honeycomb structure. This structure results in a Pt (VI) and Pt (II) mixed-valence compound with both PtSe6 octahedra and PtSe4 square net coordination configurations. Temperature-dependent electrical transport measurements suggest two distinct anomalies: a resistivity crossover, mimic to the metal-insulator (M-I) transition at ~150 K, and a resistivity plateau at temperatures below 10 K. The resistivity crossover is not associated with any structural, magnetic, or charge order modulated phase transitions. Magnetoresistivity, Hall, and heat capacity measurements concurrently suggest an existing hidden state below 5 K in this system. Angle-resolved photoemission spectroscopy measurements reveal a metallic state and no dramatic reconstruction of the electronic structure up to 200 K.

Structural and Electrochemical Properties of Type VIII Ba8Ga16-δSn30+δ Clathrate (δ ≈ 1) during Lithiation.

Clathrates of the tetrel (Tt = Si, Ge, Sn) elements are host–guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16−δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis. The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (LixBa0.17Ga0.33Sn0.67, x = 2–3) with local structures similar to those in the crystalline binary Li–Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than in β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The local structure in the clathrate featuring Ba atoms surrounded by a cage of Ga and Sn atoms is hypothesized to kinetically circumvent the formation of Li–Sn or Li–Ga crystalline phases, which results in better cycling and a lower reaction voltage. Based on the improved electrochemical performance, clathrates could act as tunable precursors to form amorphous Li alloying phases with novel electrochemical properties.

Behavior of intrinsic defects in BaF2 under uniaxial compressions: An ab initio investigation

We revisit the defects and related optical properties of one of the prototypical scintillator materials, BaF2, by means of density functional theory calculations. The interstitial F atom is found to be the most favorable defect to be formed, while it is rather difficult to create a F vacancy, Ba vacancy and Ba interstitial intrinsically, unless external forces are applied to the lattice, such as shock compression. The migration barriers for the above defects are remarkably path dependent. For a Ba vacancy, the migration barrier in the 〈001〉 (loading) direction is significantly reduced compared to those in the perpendicular 〈100〉 and 〈010〉 directions, while the migration along the 〈101〉 direction has the least value, which is surprisingly smaller than that at ambient pressure. An interstitial Ba atom prefers to move along the 〈100〉 and 〈010〉 directions in a manner similar to collective diffusion. The F vacancy has the lowest energy barrier along the 〈001〉 direction, while uniaxial strain greatly hinders the diffusion of F interstitials. We also study the role of defects on the optical absorption and find that a F vacancy, and interstitial F and Ba atoms are able to introduce pronounced changes to the spectra, whereas the Ba vacancy only shows marginal effects. The favorable migration paths for the different types of defects under strain or pressure can contribute to the design of specific ionic conductor properties under extreme conditions.

Theoretical Study of Infrared Nonlinear Optical Crystal BaGa4Se7 Tetragonal System

The electronic structure and optical properties of BaGa4Se7 tetragonal crystals are systematically studied by first principles of density functional theory. The band gap (2.918 eV) of the tetragonal system of BaGa4Se7 is 1.12 times that of the orthorhombic system by using the Heyd-Scuseria-Ernzerh (HSE06) method. The band structure showed that the top of the valence band was largely contributed by Ga 4s, 4p and Se 4p states, while the bottom of the conduction band was mainly comprised of Ga 4s, 4p, Se 4p, and Ba 5d states. This wide band gap effectively avoid the two-photon absorption during laser pumping and increase the laser damage threshold of the material. The orbital coupling between Ga and Se atoms determines the optical properties of BaGa4Se7 tetragonal crystals, while Ba atoms make little contribution to the optical properties. The calculation of optical properties shows that the static birefringence (0.076) of the BaGa4Se7 tetragonal crystal is 1.2 times that of the orthorhombic crystal system. It shows that the BaGa4Se7 tetragonal crystal material has excellent phase matching performance in a wide range of wavelengths. BaGa4Se7 crystal shows strong absorption and reflection characteristics in the ultraviolet region, and strong transmittance in the infrared region. Theoretical results indicate that BaGa4Se7 is a very promising nonlinear optical crystal in the infrared region.

Adsorption of Ba Atoms Influences the Composition, Emission, and Optical Properties of CdS Single Crystals

Adsorption of Ba Atoms Influences the Composition, Emission, and Optical Properties of CdS Single Crystals

Investigation of physical and structural properties of cs doped y1ba2cu3o7 superconductors

In this work, YBa2‑xCsxCu3O7‑δ (x= 0.05, 0.1, 0.2 and 0.3 wt. %) samples were prepared by using solid state reaction method. Some electrical, physical and structural properties of these compounds were examined by using SEM (scanning electron microscopy), XRD (X-ray diffraction), electrical resistivity, critical current density and AC susceptibility measurements, respectively. On the basis of the SEM measurements, it would seem that increasing the amount of Cs doping, the porous structures decrease and the grain size increases up to approximately 50 μm. Unit cell parameters were calculated by employing XRD measurements. On the basis of the data obtained from X-ray diffraction, Cs atoms displaced Ba atoms in the crystal structure. From the measurements of electrical resistivity at 80 K-120 K temperature, it was determined that the highest transition temperature was 91.5 K after addition of 0.05 wt. % Cs. The critical transition temperature was decreased by increasing the amount of Cs doping. Critical current density measurements on the same samples showed that as the amount of Cs doping increases, the values of Jc decrease. AC magnetic susceptibility measurements showed a sharper transition to the superconducting state in YBa2‑xCsxCu3O7‑δ (x= 0.05, 0.1, 0.2 and 0.3 wt.%) samples with the increase in the additive amount.

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 β = 90.116 (9)°. The final R-factors were obtained as R1 = 0.0354 and wR2 = 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.

Tunable magnetic anisotropy in multiferroic oxides

Weyl semimetals (WSMs) have recently stimulated intensive interest because they exhibit fascinating physical properties and also promise exciting technological applications. So far, however, the few conrmed magnetic WSMs generally have a large number of Weyl points either located away from the Fermi level (EF ) or shrouded by nontopological Fermi surface pockets. Based on first principles density functional theory calculations, we establish cubic double perovskite BaEuNiOsO6 to be a high Curie temperature (Tc) ferromagnetic WSM with magnetization along the [111] direction, just two pairs of Weyl points at the EF and Tc = 325 K. The strong ferromagnetism is attributed to the strong ferromagnetic Ni 3d-Eu 4f-Os 5d coupling induced by the substitution of half of Ba atoms with Eu atoms in double perovskite Ba2NiOsO6. Moreover, the momentum separation of one Weyl point pair is large, thus giving rise to not only a long (001) surface Fermi arc but also large anomalous Hall conductivity. Intriguingly, as a unique physical result of a ferromagnetic WSM, the (111) BaEuNiOsO6 monolayer superlattice (BaEuNiOsO6)/(BaTiO3)10, being its (111) quantum-well structure, is found to be a high temperature (Tc = 210 K) Chern insulator with a large band gap of 190 meV. Therefore, cubic double perovskite BaEuNiOsO6 will provide a superior high temperature material plotform for exploring fundamental physics of Weyl fermions and its (111) monolayer superlattices will offer a high temperature magnetic topological insulator for studying exotic quantum phenomena such as quantum anomalous Hall effect.