Nellie R. Khasanova

BI-2201 PHASES - SYNTHESIS, STRUCTURES AND SUPERCONDUCTING PROPERTIES

Abstract The Bi2+xSr2−xCuO6+° (Bi-2201) phases and La substituted Bi-2201 compounds with general formulas Bi2Sr2−xLaxCuO6+δ and Bi2.3−xSr1.7LaxCuO6+δ were prepared and characterized by X-ray powder diffraction, electron diffraction, iodometric titration and resistance measurements. The monophasic samples of Bi2+xSr2−xCuO6+δ were obtained in air at 850°C for 0.15 ≤ x ≤ 0.4, while synthesis at 740°C in oxygen flow extended this range to the stoichiometric cation composition (0 ≤ x ≤ 0.4). The superconducting transitions were not detected for these monophasic samples in contrast to the La substituted phases which exhibited superconductivity, and the highest Tc,onset = 33 K was found for the Bi2Sr1.6La0.4Cu6.33 compound. Superconductivity in the Bi2Sr2−xLaxCuO6+δ series exists in overdoped and underdoped regions. Incommensurately modulated structures of nonsuperconducting Bi2.3Sr1.7CuO6.23 phase and superconducting Bi2Sr1.7La0.3CuO6.28 phase (Tc,onset = 26 K) were refined from X-ray powder data by a Rietveld technique using the four-dimensional space group P:A2/a:−11. The maximal Cu displacements from the average position in the first structure was found to be sufficiently larger than in the latter one. The distorted structural arrangement of the (CuO2) layers in the Bi2.3Sr1.7CuO6.23 structure can be a reason for the suppression of superconductivity in this phase, while their less corrugated configuration in the La containing Bi-2201 structure leads to the existence of superconductivity.

Superconductivity at 10.2 K in the K-Bi-O system

Abstract New superconducting compound in the K–Bi–O system was obtained under high pressure. Pure perovskite phase can be prepared for K1−xBi1+xO3 in the range x=0.0–0.2. Bulk superconductivity with Tc of 10.2 K is observed for samples K1−xBi1+xO3 with x=0.0–0.1. Transition temperature Tc does not change within this interval, though deviation from the range x=0.0–0.1 leads to deterioration of superconducting properties. X-ray diffraction showed that the structure of the superconducting samples is cubic perovskite, which was confirmed by electron diffraction study. After comparing the present results with known bismuth oxide based superconductors we conclude that doping level plays a predominant role in determining the magnitude of Tc in these materials.

Perspectives on Li and transition metal fluoride phosphates as cathode materials for a new generation of Li-ion batteries

The crystal structures of various mixed Li and transition metal fluoride phosphates are reviewed, with a special focus on their applicability as cathode materials for Li-ion batteries.

Ordering of Pd2+ and Pd4+ in the Mixed-Valent Palladate KPd2O3

A new potassium palladate KPd(2)O(3) was synthesized by the reaction of KO(2) and PdO at elevated oxygen pressure. Its crystal structure was solved from powder X-ray diffraction data in the space group R3m (a = 6.0730(1) A, c = 18.7770(7) A, and Z = 6). KPd(2)O(3) represents a new structure type, consisting of an alternating sequence of K(+) and Pd(2)O(3)(-) layers with ordered Pd(2+) and Pd(4+) ions. The presence of palladium ions in di- and tetravalent low-spin states was confirmed by magnetic susceptibility measurements.

Synthesis and electrochemical performance of Li2Co1−xMxPO4F (M = Fe, Mn) cathode materials

Summary In the search for high-energy materials, novel 3D-fluorophosphates, Li2Co1− xFexPO4F and Li2Co1− xMnxPO4F, have been synthesized. X-ray diffraction and scanning electron microscopy have been applied to analyze the structural and morphological features of the prepared materials. Both systems, Li2Co1− xFexPO4F and Li2Co1− xMnxPO4F, exhibited narrow ranges of solid solutions: x ≤ 0.3 and x ≤ 0.1, respectively. The Li2Co0.9Mn0.1PO4F material demonstrated a reversible electrochemical performance with an initial discharge capacity of 75 mA·h·g−1 (current rate of C/5) upon cycling between 2.5 and 5.5 V in 1 M LiBF4/TMS electrolyte. Galvanostatic measurements along with cyclic voltammetry supported a single-phase de/intercalation mechanism in the Li2Co0.9Mn0.1PO4F material.

Extended range of superconducting bismuthates K1-xAxBiO3 (A = La, Bi, and Ca)

Abstract Synthesis and physical properties of new superconducting bismuthates, K1−xAxBiO3 (A=Bi, La, and Ca), are reported. New compounds could only be prepared in a narrow range of composition, restricted by the A-site cation size, with cubic perovskite structure. For the first two systems (A=Bi, La), Tc was found to depend strongly on composition and was enhanced upon heterovalent substitution. The data obtained and comparison with known bismuthates show undoubtedly that band filling controlled by dopant concentration is a crucial parameter for variation of Tc in this class of materials.

Synthesis and structure investigation of Sm containing Hg-1212 phases

Abstract Five samples of the HgBa 2 Sm 1− x Ca x Cu 2 O 6+δ phase were prepared. They were synthesized with different compositions, by reacting metal oxides in closed silica ampoules at 720°C for 40 h. The phase is isostructural with the tetragonal 127 K superconductor HgBa 2 CaCu 2 O 6+δ . The samples were investigated by electron microscopy, EDS analysis and X-ray powder diffraction. Electron diffraction revealed no superstructure or modulation. Rietveld structure refinements of two samples, with x = 0 and 0.5, indicated that the Hg sites were only partly occupied by mercury. A surplus of copper and samarium found in the analysis suggests that they partly substitute for mercury at this site. The refinements showed that the phase with x = 0.5 had less puckered CuO planes than HgBa 2 SmCu 2 O 6+δ . The latter showed no superconducting transition down to 15 K, and its unit-cell dimensions were not changed by oxygen or nitrogen treatments at 300°C. The Ca containing phase, HgBa 2 Sm 0.5 Ca 0.5 Cu 2 O 6+δ , had a broad superconducting transition with T c onset = 115 K. The low superconducting volume indicates that the diamagnetic signal stems from more calcium-rich crystallites.

The effect of LiFeBO3/C composite synthetic conditions on the quality of the cathodic material for lithium-ion batteries

Composite electrode materials based on LiFeBO3 are synthesized under different conditions and studied as the cathodic materials for lithiumion batteries. Composites with different degrees of iron oxidation are synthesized by annealing in a closed system with the use of metal-oxide getters. Based on the results of cyclic voltammetry and galvanostatic cycling of samples with different Fe(II) contents, it is concluded that the surface composition is the determining factor for applicability of materials to reversible processes of inter-calation-deintercalation.

New strontium and rare earth-based mixed niobium misfit sulfides

New niobium-based misfit sulfides [(Ln1/3Sr2/3S)1.5]1.15NbS2 (Ln=Sm, Tb) have been synthesized from a mixture of SrS, Ln2S3, Nb(m), and S in evacuated and sealed silica tubes by annealing at 100 ...

The superconducting bismuth-based mixed oxides

The present paper describes the synthesis, characterization of mixedvalence bismuthates with 3- or 2-dimensional perovskite-like structures and structural criteria that influence superconductivity in these compounds. Single phase samples of Sr1−xKxBiO3 were prepared for the broad range of K-content: 0.25≤x≤0.65. For these bismuthates the symmetry of the structure changes from monoclinic to orthorhombic and finally to tetragonal upon increasing the K-content thus resulting in the decrease of the Bi-O distances and reduction of the network distortions. Superconductivity with maximum Tc=12K exists in the narrow range (x≈0.5–0.6) within the stability field of the tetragonal phase (0.33≤x≤0.65), when the 3-dimensional octahedral framework has close to the ideal perovskite structure arrangement. At the same time compositions with close to optimal Bi-valence (x=0.33 and 0.43) do not show any sign of superconductivity, probably, due to structural distortions. The layered type (Ba, K)3Bi2O7 and (Ba, K)2BiO4 bismuthates belonging to the An+1BnO3n+1 homologous series were investigated. Buckling of the (BiO2) layers in the structure of the n=2 member was revealed. The formation of the n=1 bismuthate was found by Electron Microscopy and X-ray powder diffraction studies. Both types of compounds are considered to be possible candidates for new superconducting materials among bismuthates.