Soft chemistry synthesis and characterizations of fully oxidized and reduced NdBaCo2O5+δ phases δ = 0, 1

The double ordered perovskites NdBaCo₂O₅ and NdBaCo₂O₆ were prepared by soft chemistry. The samples were characterized from a structural and chemical point of view, concomitantly with their physical properties. Upon reduction, NdBaCo₂O₅ is formed with a tetragonal unit cell (a = b = 3.94 Å, c = 7.57 Å) and presents an antiferromagnetic behavior. Upon oxidation, a complete stoichiometric ordered phase NdBaCo₂O₆ with a tetragonal unit cell (a = b = 3.88 Å, c = 7.63 Å) could be obtained with a ferromagnetic and a metallic behavior. Finally it is shown that these phases are able to reversibly catch and release oxygen, suggesting a high anionic conductivity.     

Structural and magnetic properties of the double perovskite Sr2MnWO6

The nuclear and magnetic structure and the magnetic properties of the polycrystalline double perovskite Sr₂MnWO₆ have been studied. Rietveld analysis of neutron powder diffraction (NPD) data at T=295 K shows that the sample is tetragonal (space group P4₂/n, a=8.0119(4) Å, c=8.0141(8) Å). Some additional magnetic diffraction peaks were found in the NPD pattern at 10 K, which can be accounted for by antiferromagnetic ordering of spins at the Mn sites. The magnetic unit cell is doubled in all three unit axes directions (a=b=15.9984(8) Å, c=16.012(2) Å) and the manganese moments are coupled antiferromagnetically along the unit cell axes. The total magnetic moment of Mn²⁺ is found to be 2.27(7) μ_B. The antiferromagnetic behaviour was confirmed from magnetisation measurements. The transition from a paramagnetic to an antiferromagnetic state takes place at 13.0±0.1 K.     

Crystal growth and characterization of a new co-ordination complex—barium tetrakis(maleate) dihydrate

Crystals of barium tetrakis(maleate) dihydrate [Ba₄(C₄H₂O₄)₄]^?2H₂O are grown in gelated hydrosilica matrix. Single crystal X-ray diffraction studies show that the crystal system is monoclinic with space group P2₁/c. The unit cell dimensions are a=9.3721(2)  Å, b=20.5880(7)  Å, c=14.0744(4) Å, α=γ=90°, β=90.289(2)°. Powder XRD studies confirmed the single phase nature of the grown crystals. The FTIR data is in conformity with the XRD results. The TG–DTA curves of the material indicate a three-step thermal decomposition. The response of the dielectric properties in the temperature range 30 °C to 500 °C is correlated with the TG–DTA results.     

A new ternary carbide Dy2Mn2−xC5 (x=0.6): Preparation,crystal structure,and physical properties

The crystal structure, magnetic and electrical transport properties of the new ternary compound Dy₂Mn_2−xC₅ (x=0.6) have been investigated. According to X-ray powder diffraction the carbide crystallizes in its own structure type, space group I4/mmm, a=3.6421(2), c=15.7713(9) Å, R_B=0.062, R_p=0.134. The crystal structure contains isolated carbon atoms and C₂ dimers in square-bipyramidal holes and distorted bicapped square anti-prisms, respectively. Manganese atomic positions in the structure were found to be not fully occupied. Physical properties were studied in the temperature range down to 0.4 K. The electrical resistivity of Dy₂Mn_2−xC₅ (x=0.6) reveals its basically metallic nature with a positive temperature coefficient above about 30 K. A resistive anomaly at around 20 K indicates the appearance of an antiferromagnetic superzone boundary gap at low temperatures. A phase transition towards long range antiferromagnetic magnetic ordering below 19 K is further revealed by heat capacity and ac susceptibility data. Magnetization data refer to a non-trivial nature of the magnetic ground state which may be caused by the intrinsic structural disorder associated with random vacancies at the Mn site.     

Synthesis,crystal structure,spectroscopic characterization and optical properties of bis(4-acetylanilinium) tetrachlorocobalt (II)

The chemical preparation, crystal structure, spectroscopic investigations and optical features are given for a novel organic–inorganic hybrid material [C₈H₁₀NO]₂CoCl₄.The compound is crystallized in the orthorhombic space group Cmca, with the following unit cell parameters: a=19.461(2) Å, b=15.523(2) Å, c=13.7436(15) Å, and Z=8. The atomic arrangement shows an alternation of organic and inorganic layers along the b-axis. The cohesion between these entities is performed by N–H…Cl and N–H…O hydrogen bonds and π–π stacking interactions.Infrared and Raman spectra at room temperature are recorded in the 4000−400 and 4000−0 cm⁻¹ frequency regions, respectively and analyzed on the basis of literature data. This study confirms the presence of the organic cation [C₈H₁₀NO]⁺ and of the [CoCl₄]²⁻ anion. UV–vis spectroscopy results showed the indirect transition with band gap energy 2.98 eV.     

Dipotassium sodium niobium dioxide tetrafluoride,K2NaNbO2F4, crystal structure and characterization

The paper presents a new data on the crystal structure of K₂NaNbO₂F₄. Single crystals of K₂NaNbO₂F₄, were obtained from the system of KF–NaF–Nb₂O₅. The compound is cubic, space group Fm3?m (No. 225), and the unit cell parameters are a=8.4726(4) Å, Z=4, Volume=608.21(5) Å³. The structure was solved by the direct methods and refined to the reliability factors R₁=0.0116 (wR₂=0.0302). Its structure can be described as three-dimensional frameworks formed of (0 1 0) [Na₂Nb₂O₄F₈]∞ layers stacked along b axis. In the framework, niobium, oxygen, fluorine atoms form a rare [NbO₂F₄]^3? anion group in an anhydrous solid state environment. The IR spectrum further confirmed the presence of NbO₂ and NbF₄ groups in the structure. The thermal analysis suggests that K₂NaNbO₂F₄ is an incongruently melting compound.     

Interfacial reactions of Ba2YCu3O6+z with coated conductor buffer layer,LaMnO3

Chemical interactions between the Ba₂YCu₃O_6+x superconductor and the LaMnO₃ buffer layers employed in coated conductors have been investigated experimentally by determining the phases formed in the Ba₂YCu₃O_6+x–LaMnO₃ system. The Ba₂YCu₃O_6+x–LaMnO₃ join within the BaO–(Y₂O₃–La₂O₃)–MnO₂–CuO_x multi-component system is non-binary. At 810 °C (p_O2 = 100 Pa) and at 950 °C in purified air, four phases are consistently present along the join, namely, Ba_2?x(La_1+x?yY_y)Cu₃O_6+z, Ba(Y_2?xLa_x)CuO₅, (La_1?xY_x)MnO₃, (La,Y)Mn₂O₅. The crystal chemistry and crystallography of Ba(Y_2?xLa_x)CuO₅ and (La_1?xY_x)Mn₂O₅ were studied using the X-ray Rietveld refinement technique. The Y-rich and La-rich solid solution limits for Ba(Y_2?xLa_x)CuO₅ are Ba(Y_1.8La_0.2)CuO₅ and Ba(Y_0.1La_1.9)CuO₅, respectively. The structure of Ba(Y_1.8La_0.2)CuO₅ is Pnma (No. 62), a = 12.2161(5) Å, b = 5.6690(2) Å, c = 7.1468(3) Å, V = 494.94(4) Å³, and D_x = 6.29 g cm^?3. YMn₂O₅ and LaMn₂O₅ do not form solid solution at 810 °C (p_O2 = 100 Pa) or at 950 °C (in air). The structure of YMn₂O₅ was confirmed to be Pbam (No. 55), a = 7.27832(14) Å, b = 8.46707(14) Å, c = 5.66495(10) Å, and V = 349.108(14) Å³. A reference X-ray pattern was prepared for YMn₂O₅.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

Vibrational study,phase transitions and electrical properties of 4-benzylpyridinium monohydrogenselenate

The title compound C₆H₅CH₂C₅H₄NH⁺·HSeO₄⁻ crystallizes in the orthorhombic system with the space group Pbca and the following unit cell dimensions: a=27.449(5) Å; b=10.821(6) Å and c=8.830(1) Å.The structure consists of infinite parallel two-dimensional planes built of HSeO₄⁻ anions and C₆H₅CH₂C₅H₄NH⁺ cations mutually.Differential scanning calorimetry study on 4-benzylpyridinium monohydrogen-selenate was carried out. A high temperature second order phase transition at 363 K was found and characterized by electric measurements. The Raman of polycrystalline sample has been recorded at different temperature between 297 and 373 K.The conductivity relaxation parameters associated with some H⁺ conduction have been determined from an analysis of the M′′/M′′_max spectrum measured in a wide temperature range. An appearance of the superionic phase transition in 4-BSe is closely related to a liberation or even a rotation increase of HSeO₄⁻ groups with heating.     

Stabilization of high spin FCC Fe in (Fe/Pd)n multilayers

Polycrystalline (Fe/Pd)_n multilayers are grown onto sapphire substrates at room temperature in a UHV system. The number of periods n=40 and the thickness of Pd layers of t_Pd=4 nm are kept constant, whereas the thickness of the Fe layers is varied from 1.5 to 5 nm. Structural properties are studied by in situ reflection high energy diffraction (RHEED), scanning tunnelling microscopy (STM) and ex situ by X-ray diffraction at small angles and large angles. Analyzing the experimental data using the program SUPREX we obtain interplanar distances of d_Fe=2.03±0.01 Å for an Fe layer thickness larger than about 2.5 nm as expected for (1 1 0) planes of BCC Fe. For Fe layers with thicknesses less than about 2.5 nm the interplanar distance is d_Fe=2.1±0.01 Å, which is close to the distance between (1 1 1) planes of FCC Fe with a lattice parameter of a=3.64 Å. Magnetic susceptibility measurements at temperatures between 1.5 and 300 K for (Fe/Pd)_n multilayers with FCC Fe yield a magnetic moment per Fe atom of μ=2.7±0.1 μ_B, which is about 20% larger compared to μ=2.2 μ_B for BCC Fe. We show that the occurrence of the large magnetic moment originates from FCC Fe being in the high spin (HS) state rather than from polarization effects of Pd at Fe/Pd interfaces.     

Synthesis,crystal growth and characterization of a semiorganic material: Calcium dibromide bis(glycine) tetrahydrate

Single crystals of semiorganic material calcium dibromide bis(glycine) tetrahydrate were grown from aqueous solution. The crystal belongs to monoclinic system, with a = 13.261(5) Å, b = 6.792(2) Å, c = 15.671(9) Å and β = 91.68(4)°. The presence of the elements in the title compound was confirmed by energy dispersive X-ray analysis. The solubility and metastable zone width were found. The grown crystals were tested by powder XRD, FTIR, Thermo Gravimetric and Differential Thermal Analysis, UV–vis–NIR analysis, dielectrical and mechanical studies. The transmittance of calcium dibromide bis(glycine) tetrahydrate crystal has been used to calculate the refractive index n, the extinction coefficient K and both the real ɛ_r and imaginary ɛ_i components of the dielectric constant as functions of wavelength. The optical band gap of calcium dibromide bis(glycine) tetrahydrate is 3.23 eV.     

Long RE123 coated conductors with high critical current over 500 A/cm by IBAD/PLD technique

We have developed long RE₁Ba₂Cu₃O_7?X (RE123) coated conductors with large current capacity by the ion beam assisted deposition (IBAD) and the pulsed laser deposition using hot wall heating (HW-PLD) technique. As a result, we could fabricate an 8 m-long Gd₁Ba₂Cu₃O_7?X (Gd123) coated wire with the minimum and maximum critical current (I_c) of 951 A/cm-w and 1003 A/cm-w at 77 K, 0 T, respectively, measured in 0.7 m-long sections by the standard 4-probe technique. Furthermore, we succeeded in preparation of over 600 m-long Gd123 coated wire with the uniform I_c distribution over 600 A/cm-w. It had average, maximum and minimum I_c of 665, 698, 609 A/cm-w, respectively. The n-values of the sample showed the maximum I_c and minimum I_c were 40 and 36, respectively. As a result, we set the new world record of I_c × L value as 374535 A m (= 609 A × 615 m). The in-field performance of this long wire was quite high as well; the minimum I_c exceeded 50 A/cm-w at 77 K, 3 T.     

Oxide ion conduction mechanism in RE9.33(SiO4)6O2 and Sr2RE8(SiO4)6O2 (RE = La,Nd) from neutron powder diffraction

The oxide ion conduction mechanism was clarified for high purity RE_9.33(SiO₄)₆O₂ and Sr₂RE₈(SiO₄)₆O₂ (RE = La and Nd) by Rietveld and maximum entropy method (MEM) analysis using neutron powder diffraction data collected at room temperature. All the compounds had an apatite-type structure in the space group P6₃/m. Neither site splitting nor interstitial sites of the oxide ion was observed. RE_9.33(SiO₄)₆O₂ had cation vacancies only at the 4f site. In Sr₂RE₈(SiO₄)₆O₂, the 4f sites were fully occupied by strontium and rare earths with a molar ratio of 1 : 1. Also, in RE_9.33(SiO₄)₆O₂, the oxide ion at the hexagonal channel site had a large displacement along the c-axis. This large displacement is induced by cooperative rotation of SiO₄ tetrahedra around rare earths at the 4f site through oxide ion polyhedra around another rare earth at the 6h site. The displacement, enhanced by a vacancy in the 4f site, is directly related to oxide ion conduction in RE_9.33(SiO₄)₆O₂.     

The layered iron phosphate KMgFe(PO4)2: Crystal structure,Mössbauer spectroscopy and ionic conductivity

A new iron phosphate, KMgFe(PO₄)₂ has been synthesized and investigated by X-ray diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic space group C2/c with the parameters a = 18.529(7) Å, b = 5.402(3) Å, c = 9.374(9) Å, β = 120.64(5)° and Z = 4. Its original structure can be described as the stacking along the [101] direction of [MgFe(PO₄)^?₂]_∞ layers of corner-sharing MO₄ (M = 0.5 Fe + 0.5 Mg) and PO₄ tetrahedra. The K⁺ ions are occupying the inter-layer space. The Mössbauer spectroscopy confirms the occurrence of only tetrahedral Fe³⁺ ions and gives a definitive proof of the disordered character of their distribution. Ionic conductivity results obtained by the impedance spectroscopy technique show that this material is a two-dimensional ionic conductor, with low activation energy, 0.51 eV, that is interpreted on the basis of two-dimensional pathways.     

A single-crystal study of the electrochemically Li-ion intercalated spinel-type Li4Ti5O12

Single crystals of Li_4 + xTi₅O₁₂ were prepared by means of electrochemical Li-ion intercalation technique using parent Li₄Ti₅O₁₂ single crystals. The obtained Li_4 + xTi₅O₁₂ (x = 1.35) crystallizes in the cubic spinel-related type structure, space group Fd3?m, and lattice parameters of a = 8.346(2) Å and V = 581.3(5) Å³ and Z = 8. The Li-ion intercalated sites were successfully determined to be both the 8a and 16c sites by using the difference Fourier synthesis map. The structure was determined by single-crystal X-ray structure analysis and refined to the conventional value of R = 3.7% for 132 independent observed reflections. The chemical composition has been determined to be Li_5.35Ti₅O₁₂ from the result of site-population refinements. In addition, theoretical electron density distributions and total energy were calculated for three postulated compounds of “Li_4.5Ti_4.5O₁₂” and “Li_4.5 + xTi_4.5O₁₂” with x = 1.5 and 3.0.     

Synthesis,growth and characterization of a semiorganic nonlinear optical single crystal: L-Valine cadmium bromide

A semiorganic nonlinear optical material L-valine cadmium bromide was synthesized and single crystal grown from an aqueous solution by the method of slow evaporation technique at room temperature. The grown crystal was characterized by Powder X-ray diffraction and FT IR studies. The LVCB crystallizes in monoclinic system with cell parameters a = 10.144(2) Å, b = 5.54(1) Å, c = 12.07(2) Å, β = 109.115(2)° with space group P₂₁. Thermal behavior and stability of crystal were studied using thermogravimetric analyses (TGA) and differential thermal analysis (DTA) techniques. The suitability of this material for NLO application was studied by optical absorption studies and second harmonic generation (SHG) efficiency measurement by Kurtz–Perry powder method.     

High resolution emission spectroscopy of the E2Π–X2Σ+ transition of SrH and SrD

Emission spectra of SrH and SrD have been studied at high resolution using a Fourier transform spectrometer. The molecules have been produced in a high temperature furnace from the reaction of strontium metal vapor with H₂/D₂ in the presence of a slow flow of Ar gas. The spectra observed in the 18 000–19 500 cm^?1 region consist of the 0–0 and 1–1 bands of the E²Π–X²Σ⁺ transition of the two isotopologues. A rotational analysis of these bands has been obtained by combining the present measurements with previously available pure rotation and vibration–rotation measurements for the ground state, and improved spectroscopic constants have been obtained for the E²Π state. The present analysis provides spectroscopic constants for the E²Π state as ΔG(½) = 1166.1011(15) cm^?1, B_e = 3.805503(32) cm^?1, α_e = 0.098880(47) cm^?1, r_e = 2.1083727(89) Å for SrH, and ΔG(½) = 839.1283(23) cm^?1, B_e = 1.918564(15) cm^?1, α_e = 0.034719(23) cm^?1, r_e = 2.1121943(83) Å for SrD.     

Synthesis and characterization of (Bi,Cu)Sr2(RE,Ca)Cu2Oz (RE: Y or rare-earth element)

Samples with nominal compositions of x = 0–0.1 in (Bi_(1+3x)/3Cu_(2?3x)/3)Sr₂(RE_1?xCa_x)Cu₂O_z ((Bi,Cu)-“1-2-1-2”; RE: Y or rare-earth element) were synthesized by a solid-state reaction method and characterized by means of X-ray diffractometry (XRD). It is confirmed that the (Bi,Cu)-“1-2-1-2” forms only when RE = Y, Dy and Ho. Single- or nearly single-phase samples are obtained for x = 0–0.05 and the Ca-free composition of this compound is determined to be (Bi_1/3Cu_2/3)Sr₂RECu₂O_z. Since ionic radii of Y, Dy and Ho are very close to each other and this seems to be an essential factor for the stability of the (Bi,Cu)-“1-2-1-2”.     

Infrared-to-visible up-conversion luminescence and energy transfer of RE3+/Yb3+(RE = Ho,Tm) co-doped SrIn2O4

Near-infrared excited up-conversion phosphors of RE³⁺/Yb³⁺(RE = Ho, Tm) co-doped SrIn₂O₄ were synthesized by a solid-state reaction method. X-ray diffraction analysis revealed the phase composition of those samples, and the up-conversion spectroscopic properties were studied in terms of up-conversion emission spectra. Under 980 nm near-infrared laser excitation, strong green emission with the peak at 546 nm was observed in SrIn₂O₄: Ho³⁺/Yb³⁺, which can be assigned to the characteristic ⁵S₂(⁵F₄) → ⁵I₈ transition of Ho³⁺. Furthermore, SrIn₂O₄: Tm³⁺/Yb³⁺ showed bright blue emission with the peak at 486 nm, which is associated with the ¹G₄ → ³H₆ transition of Tm³⁺. The UC power studies indicated that the luminescence of SrIn₂O₄: Ho³⁺/Yb³⁺ and SrIn₂O₄: Tm³⁺/Yb³⁺ are attributed to two-photon and three-photon process, respectively. The possible UC luminescence mechanism and energy transfer in SrIn₂O₄: RE³⁺/Yb³⁺ were discussed.     

The evolution of electromagnetic response at low frequencies with the development of superconducting condensation in Tl2Ba2CaCu2O8+δ

We report the in-plane temperature dependent ac impedance spectrum of Tl₂Ba₂CaCu₂O_8+δ (Tl-2212) single crystal film with thickness 3000 Å and T_c = 96 K. In process of the superconducting condensation, the impedance spectrum z(ω,T₀) changed considerably and was very similar with the evolution of the spectrum under various dc bias voltages in the shallow superconducting state. The spectrum weight transfers from high frequency regions to lower ones and eventually diverges towards the dc limit. From the analysis, it seems that the superconducting ‘islands’ form first and then grow larger, till the formation of a ‘continent’. The impedance spectrum z(ω,B_I) at various dc bias B_I have also been studied.