J.P. Attfield

New anion-deficient cubic perovskites: Ba2In1 −xCo1 +xO5 +δ(0 ≤x≤ 0.8) and Ba2 −xLaxCoInO5 +δ(0.2 ≤x≤ 0.8)

The new compound Ba2InCoO5 + δ, which has a cubic perovskite structure (a = 4.1587(3) A) at high temperatures, was prepared by heating mixtures of BaCO3, In2O3 and Co3O4 in air at 1150 °C for 20 h. Heat treatment of Ba2InCoO5 + δ in air at 850 °C for 72 h revealed a phase transformation into a brownmillerite-type structure. To stabilize a cubic perovskite phase at moderate temperatures, the solid solutions Ba2In1 − xCo1 + xO5 + δ, 0 ≤ x ≤ 0.7 and Ba2 − xLaxCoInO5 + δ, 0 ≤ x ≤ 0.8 were prepared. X-Ray diffraction revealed that the cubic perovskite structure is stable only for Ba2In1 − xCo1 + xO5 + δ, 0.4 ≤ x ≤ 0.6 and Ba1.2La0.8CoInO5 + δ, Ba1.4La0.6CoInO5 + δ upon heat treatment in air at 850 °C for 72 h.

Synthesis, crystal structure and magnetism of Sr3Sb2NiO9 - A ferrimagnetic perovskite

Abstract A new nickel(II) oxide, Sr 3 Sb 2 NiO 9 , has been synthesised at 1200 °C. Rietveld fits to the powder synchrotron X-ray diffraction pattern show that this compound has orthorhombic symmetry [ a = 5.6237(1), b = 5.6442(1), c = 7.9574(1) A at 300 K ] and adopts a pseudo-double perovskite structure with Sb:Ni ratios of 40:60 and 93:7 at alternate cation sites. Powder neutron refinements demonstrate that space group symmetry is Pnnm between 1.5 and 300 K due to partly disordered rotations of the Sb/NiO 6 octahedra. Sr 3 Sb 2 NiO 9 behaves as a Curie-Weiss paramagnet at high temperatures with μ eff = 3.25(1) BM per Ni 2+ ion and ⊖ = − 119(1) K reflecting dominant antiferromagnetic spin-spin interactions, but a weak ferromagnetic component observed below the ordering temperature of 20 K suggests overall ferrimagnetic behaviour.

Crystal structure of Tl0.5Pb0.5Sr2Ca2Cu3O9 at 300 K and around Tc (118 K)

Abstract The crystal structure including the cation distribution, of a polycrystalline sample of nominal composition Tl 0.5 Pb 0.5 Sr 2 Ca 2 Cu 3 O 9 with T c = 118.2 K has been determined using resonant synchrotron X-ray diffraction data collected at the Cu K, Tl L III and Sr K edges and time-of-flight powder neutron diffraction data. No oxygen deficiency was observed, but cation disorder at all the non copper sites according to the formula (Tl 0.60 Pb 0.40 )(Sr 1.60 Ca 0.40 )(Ca 1.93 Tl 0.07 ) Cu 3 O 9 gives a mean hole concentration of 0.18(1) per Cu atom for the three CuO 2 planes, consistent with the high T c for this material. Analysis of five time-of-flight powder neutron diffraction data between 80 and 150 K have revealed a possible discontinuity in the variation of the c lattice parameter at T c , due to an anomaly in the position of the apical oxygen atoms.

The structure of new nickel(I) oxides: LnSr5Ni3O8 (Ln = Y, Dy, Ho, Er and Tm)

Abstract Stoichiometric oxides of 3d9 nickel(I), LnSr5Ni3O8 (Ln = Y, Dy, Ho, Er and Tm), have been prepared through the hydrogen reduction of LnSr5Ni3O11, resulting in a change from a tetragonal K2NiF4 type structure to an orthorhombic Sr2CuO3 arrangement in which 1 3 of the bridging oxygen atoms are missing from chains of apex-linked nickel oxide square planes.

YSr5Ni3O8–-a new nickel(I) oxide with a defect Sr2CuO3 structure

A stoichiometric oxide of 3d9 nickel(I), YSr5Ni3O8, has been prepared through the hydrogen reduction of YSr5Ni3O11, resulting in a change from a tetragonal K2NiF4 type structure to an orthorhombic Sr2CuO3 arrangement in which 1/3 of the bridging oxygen atoms are missing from chains of apex-linked nickel oxide square planes.

Synthesis, crystal structure and properties of In-containing 1212-type compounds

Abstract A new series of solid solutions (Bi 0.35 In 0.65 ) 1− x Pb x Sr 2 Gd 0.6 Ca 0.4 Cu 2 O y ( x = 0−0.5) has been synthesised and characterised by means of powder X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometric analysis, and magnetic and resistivity measurements. High temperature preparations lead to the appearance of “bulk” superconducting properties which, however, can be attributed to the formation of a small amount of a Bi-2212 phase. The structure of a highly phase pure nonsuperconducting sample with composition Bi 0.21 In 0.33 Pb 0.25 Sr 2 Gd 0.89 Ca 0.11 Cu 2.21 O 7+δ has been Rietveld refined using powder synchrotron X-Ray diffraction data.

Powder diffraction studies of a 118 K Tl,Pb-1223 superconductor

Abstract The cation distribution in a polycrystalline sample of starting composition ‘Tl 0.5 Pb 0.5 Sr 2 Ca 2 Cu 3 O 9 ‘ with Tc(zero resistivity) = 118.2 K and Δ Tc = 1 K has been determined from resonant synchrotron X-ray diffraction data collected at the Cu K, Tl L III , Pb L III and Sr K edges. Cation disorder is found at all the non-Cu sites according to the formula (Tl 0.47 Pb 0.53 )(Sr 1.58 Ca 0.42 )(Ca 1.94 Tl 0.06 )Cu 3 O 9 . Assuming the presence of Tl 3+ and Pb 4+ , this formula gives a mean oxidation state of +2.14 for the three copper atoms, consistent with the high Tc of this material. Time-of-flight powder neutron diffraction data between 100 and 150 K have been collected to discover any structural anomalies around Tc.

Charge disorder effects in 3d transition metal oxide perovskites

Abstract The effects of the random electrostatic potential due to differences in formal charge between A site R3+ (lanthanide, Y), M2+ (Ca, Sr, Ba) and Th4+ cations have been investigated in ferromagnetic AMnO3 and superconducting A2CuO4 perovskites. Series of samples in which the mean A site charge and the mean and variance of the A cation radius distribution are held constant, but the A site charge variance increases, show no significant changes of the electronic (Curie or superconducting) transition temperatures. The effect of the A cation random potentials on electronic transitions in the 3d metal oxide perovskites are insignificant in comparison to the lattice effects from the differing cation sizes.

Chemistry and structure of borate-containing materials LnSr2Cu3-xBxO7-δ

Abstract Compositions LnSr 2 Cu 3-x B x O 7 (Ln = La, Nd, Gd, Y, Yb) have been investigated at 1000°C starting from a citrate gel precursor. Almost single phase polycrystalline samples were obtained for Ln = Gd and Y up to x = 0.8 and 0.75 respectively. Calcium substituted samples BSr 2 (Y 1-y Ca y )Cu 2 O 7 ( y = 0, 0.1, 0.2, 0.4, 0.6) were prepared by the same method with phase purity deteriorating on increased calcium substitution. Superconductivity is not observed at these high boron doping limits. The larger lanthanides (La, Nd) studied showed evidence of the 1212 type compound but the phase purity was low, indicating that the limit of B substitution was low. The smaller Yb showed no evidence of the 1212 phase. The YSr 2 B 0.75 Cu 2.25 O 7-δ , material is orthorhombic with cell parameters a=3.8203(5) A , b=3.8381(5) A , c=10.983(1) A and has been investigated by time-of-flight powder neutron diffraction and hogh resolution electron microscopy.

Phase separation and cation distributions in Tl-2201 from resonant synchrotron X-ray diffraction

Orthorhombic and tetragonal Tl-2201 (‘Tl2Ba2CuO6+δ’) samples have been studied using resonant synchrotron X-ray powder diffraction data at energies just below the Cu K and Tl LIII absorption edges. The resonant contributions enable us to demonstrate that Cu substitutes at the Tl site; the tetragonal structure is stabilised by a higher (5.5%) degree of substitution than the orthorhombic material whereit is <1%. A slight splitting of some diffraction peaks of orthorhombic Tl-2201 is consistent with separation into two phases due to the segregation of interstitial oxygens, giving one phase with δ = 0 and another with δ = 0.3 that displays an incommensurate superstructure. These two phases are respectively too under- and over-doped to superconduct.