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Journal ArticleDOI

Phase formation and superconductivity in REBaSrCu3−x(PO4)xOy (0 ≤ x ≤ 0.3)

15 Jul 1997-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 280, Iss: 4, pp 327-334
Abstract: Oxy-anion (PO 4 3− ) substituted phases of the composition REBaSrCu 2.8 (PO 4 ) 0.2 O y have been synthesized. Single phase formation is achieved only for the larger rare earths (La → Ho and Y) and all the phases crystallize in the tetragonal 123 structure. IR studies confirm the presence of a phosphate group in the structure. The total oxygen content (including that associated with the oxy-anion PO 4 3− ) has been found to be in the range 7.01 to 7.10 per formula unit. Except for RE = La, Nd, Yb and Lu, all the phases exhibit superconductivity and the T c,zero values vary from 18 to 38 K. The T c,zero increases with decreasing size of RE 3+ . ErBaSrCu 3 O 7 is multiphasic and single phase formation is achieved for the first time by phosphate substitution at the copper site. Single phase formation is encountered for x = 0.10 and 0.15 with T c,zero values of 54 and 37 K respectively. more

Topics: Formula unit (51%)
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Book ChapterDOI
Pavel Karen1, Arne Kjekshus1Institutions (1)
Abstract: Publisher Summary This chapter presents the phase diagrams and thermodynamic data for selected cuprates of alkaline-earth (A) and rare-earth (R) elements except Sc, along with the binary to quintenary oxides, and relevant solid-solution series with other elements. Short information on crystal structure is listed for each phase giving it its identity, as well as the concise chemical information which defines its character. The chemistry of phases is illustrated in mostly subsolidus isothermal phase diagrams, drawn after original sources, and referring to diverse chemical conditions defined by partial pressures of oxygen in particular. Reactivity towards CO2 and formation of oxide carbonates are treated systematically as well, having been one of the major experimental obstacles in pursuit of data relevant to pure oxides. The chapter also discusses the essential thermodynamic data for evaluations of phase equilibria appear in the form of entropies and enthalpies at standard and phase-transition temperatures together with heat-capacity functions. Other possibilities are temperature polynomials for standard Gibbs energies of formation or for partial pressures of gaseous components. more

12 citations

Journal ArticleDOI
Abstract: We present X-ray and magnetization results for the compound [Y0.75Ca0.25]SrBaCu3−x(PO4)xOy with 0.0⩽x⩽0.30 synthesized at normal pressure and temperature. X-ray diffraction patterns show that for x= 0.0 the compound crystallizes into an orthorhombic phase. For increasing x a tetragonal phase is obtained. The Rietveld method was used to refine lattice constants. The magnetization measurements show that the samples were all superconductors over a range of temperatures from 10 to 100 K. The diamagnetic transition temperature Tc decreases with increasing (PO4)3− concentration (Tc=55 K for x=0.0 and Tc=35 K for x=0.30). more

4 citations

Journal ArticleDOI
Abstract: We present the composite [Y 1−x Ca x ]SrBaCu 2.80 (PO 4 ) 0.20 O y (0.10≤x≤0.40) prepared at normal temperature and pressure conditions. X-ray diffraction patterns show that samples containing Ca crystallize in a 123 tetragonal structure with small amounts of impurities. The Rietveld method was used to refine the lattice constants. Ac and dc susceptibility measurements using a SQUID show that the materials are superconductors independent of Ca content. In the normal region the measurements of χ DC show a typical Curie-Weiss law behavior. more

3 citations

Reference EntryDOI
J. Paul Attfield1Institutions (1)
15 Dec 2011-
Abstract: Phosphates contain oxyanions of phosphorus(V). The most common anion is the orthophosphate group PO4 3 −, which is found in many solid phosphates, including hydrated and acid phosphate salts. Oligomeric polyphosphate chains P n O3 n +1 ( n +2)− up to n = 6 and cyclophosphate rings P n O3 n n − up to n = 12 are also observed, and a unique cage ultraphosphate anion P8O23 6− is found in the Na3FeP8O23 structure. Polymeric phosphate anions include the infinite chain catenaphosphate anion (PO3 −)∞ and the ultraphosphate networks found in CaP4O11 and the lanthanide MP5O14 structures. Many compound anions and neutral frameworks such as silicophosphates, aluminophosphates, and molybdenum phosphates also exist. Phosphate species are characterized through P–O stretching and bending vibrations in infrared and Raman spectroscopies, and by 31P NMR. Phosphate structures are generally rigid, resistant to chemical attack, and (when anhydrous) insoluble and thermally stable. Some phosphate crystals have important physical properties such as ferroelectricity in KH2PO4 (potassium dihydrogenphosphate, KDP). Diffusion of extra-framework ions leads to potential uses of solid phosphates as ion exchangers and conductors, for example, NASICON based on NaZr2(PO4)3, and LiFePO4 as a cathode material for lithium-ion batteries. Vanadium phosphates are important selective oxidation catalysts. Large pore phosphates in which molecules can be adsorbed and undergo acid-catalyzed reactions have been intensively studied. These materials are crystalline microporous solids such as aluminophosphates, or lamellar structures, typically based on α-Zr(HPO4)2·H2O that can be pillared. This area of interest has led to the synthesis of many new organically templated metal phosphates, usually through hydrothermal reactions. Hydrated and acid orthophosphates can also be prepared in solution, and anhydrous phosphates are synthesized by direct high-temperature reactions and from phosphate-rich melts or fluxes. Slow cooling of melts is used to grow crystals, and quenching can result in many stable phosphate glasses. Phosphate anions do not absorb significantly in the UV–visible region and so solid phosphates also find use as optical materials such as phosphors, nonlinear crystals (e.g., KTiOPO4), and lasers. Solid phosphates constitute many minerals, notably apatites, which are also found in living organisms as rigid components such as bones and teeth. Synthetic calcium phosphate biomaterials are used for bone implants. Keywords: orthophosphate; phosphate; ionically conducting phosphates; microporous phosphate materials; mineral phosphates; nonlinear optical phosphate materials; condensed phosphate polyanions; layered phosphate materials; biomaterial phosphates more

2 citations

Journal ArticleDOI
Abstract: The compounds GdBaSr 1− x Nd x Cu 3 O y (where x = 0, 0.1, 0.2 and 0.3) were prepared using the solid-state reaction technique. The single phase and microrange crystalline nature of the compounds were studied by powder X-ray diffraction and SEM analysis. The electrical resistivity and magnetic properties of the compounds were studied as a function of temperature. A decrease in superconducting transition temperature for an increase in Nd substitution was observed. A decreasing trend of diamagnetic strength and an increasing trend of magnetic moment of the samples with Nd substitution were observed from magnetization measurement. The optimal sintering temperature of the compounds was found to be 950 °C. more

1 citations

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Kazuo Nakamoto1Institutions (1)
01 Jan 1978-
Abstract: Inorganic molecules (ions) and ligands are classified into diatomic, triatomic, four-atomic, five-atomic, six-atomic, and seven-atomic types, and their normal modes of vibration are illustrated and the corresponding vibrational frequencies are listed for each type. Molecules of other types are grouped into compounds of boron, carbon, silicon, nitrogen, phosphorus, and sulfur, and the structures and infrared (IR)/Raman spectra of select examples are shown for each group. Group frequency charts including band assignments are shown for phosphorus and sulfur compounds. Other group frequency charts include hydrogen stretching frequencies, halogen stretching frequencies, oxygen stretching and bending frequencies, inorganic ions, and metal complexes containing simple coordinating ligands. Keywords: inorganic compounds; coordination compounds; diatomic molecules (ligands); triatomic molecules (ligands); four-atomic molecules (ligands); five-atomic molecules (ligands); six-atomic molecules (ligands); seven-atomic molecules (ligands); boron compounds; carbon compounds; silicon compounds; nitrogen compounds; phosphorus compounds; sulfur compounds; group frequency charts more

15,594 citations

Journal ArticleDOI
Abstract: We have investigated the composition YSr2Cu3-xMxOy and obtained the 123-structure for M= Li, Al, Ti, V, Cr, Fe, Co, Ga, Ge, Mo, W and Re. Superconductivity is observed for the compounds with M=Ti, V, Fe, Co, Ga, Ge, Mo, W and Re at low levels of substitution context x. The highest Tzeroc is 73 K for the compound YSr2Cu2.85Re0.15O7.12. Tcs are enhanced by decreasing x or increasing y, which draw the rise of hole concentration pave (Cu2+p). Except for the compounds with M=V and Cr, the structures are tetragonal, while those of the compounds YSr2Cu3-xCrxOy are orthorhombic, and YSr2Cu3-x VxOy shows the structural transition from tetragonal to orthorhombic by HIP treatment with the simultaneous transition from superconductivity to metallic transport property. This Sr-based 123-structure is stabilized by doping elements with ionic radii=0.35-0.49 A or 0.525-0.62 A supposing 4- or 6-coordination, respectively, except for M=Li. more

130 citations

Journal ArticleDOI
Peter R. Slater1, Colin Greaves1Institutions (1)
Abstract: The possibility of synthesising phases of general composition YSr 2 Cu 3− x M x O 7± y has been examined for a wide variety of metals M. Single phase tetragonal products (typically a = 3.83 A , c = 11.5 A ) can be synthesised provided that the concentration of M is sufficiently large ( x > 0.5), and M has a preference for the Cu(1) sites (the four-coordinate sites) of the YBa 2 Cu 3 O 7 , structure. Neutron diffraction has demonstrated that a high degree of disorder exists in the (001) planes containing the M cations and, in particular, significant oxygen displacements are found. The non-existence of the unsubstituted variant YSr 2 Cu 3 O 7 is explained in terms of the high degree of compressive stress on the Cu(1) sites which could exist in such a material. more

102 citations

Journal ArticleDOI
Yuzuru Miyazaki1, Hisanori Yamane1, N. Ohnishi1, Tsuyoshi Kajitani1  +4 moreInstitutions (2)
Abstract: The crystal structure of a new compound, (C0.4Cu0.6)Sr2(Y0.86Sr0.14)Cu2O7, is derived from the structure of YBa2Cu3O7. Forty percent of CuO chains in the YBa2Cu3O7 structure are replaced by CO3 groups. This new compound has a superstructure along the a-axis and the c-axis. Diffuse superlattice reflections having periods of a∗/2-a∗/3 and c∗/2 were observed in electron diffraction patterns. Locally ordered distributions of C and Cu atoms were seen high-resolution images taken by transmission electron microscopy with an incident beam parallel to [010]. The basic structure of this superstructure was determined by neutron powder diffraction, assuming orthorhombic symmetry with the space group, Pmmm (lattice constants: a=3.8278(2), b=3.8506(2) and c=11.1854(5) A ). more

92 citations