Showing papers by "J. Paul Attfield published in 2010"
TL;DR: The structural and electronic properties of BiCoO(3) under high pressure have been investigated and results show that Co(3+) is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present.
Abstract: The structural and electronic properties of BiCoO(3) under high pressure have been investigated. Synchrotron X-ray and neutron powder diffraction studies show that the structure changes from a polar PbTiO(3) type to a centrosymmetric GdFeO(3) type above 3 GPa with a large volume decrease of 13% at room temperature revealing a spin-state change. The first-order transition is accompanied by a drop of electrical resistivity. Structural results show that Co(3+) is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present. The pressure-temperature phase diagram of BiCoO(3) has been constructed enabling the transition temperature at ambient pressure to be estimated as 800-900 K.
146 citations
TL;DR: Both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio, and colossal magnetoresistances (CMR) are observed in the least doped sample.
Abstract: A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN2−x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4−yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN2−x perovskites that show a wide range of compositions −0.16 ≤ x ≤ 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2−x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = −0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified.
94 citations
TL;DR: A miniature diamond anvil cell for magnetization measurements in a widely used magnetic property measurement system commercial magnetometer built around a superconducting quantum interference device capable of achieving pressures in excess of 10 GPa while allowing measurements to be performed with the maximum sensitivity of the magnetometer.
Abstract: We have developed a miniature diamond anvil cell for magnetization measurements in a widely used magnetic property measurement system commercial magnetometer built around a superconducting quantum interference device. The design of the pressure cell is based on the turnbuckle principle in which force can be created and maintained by rotating the body of the device while restricting the counterthreaded end-nuts to translational movement. The load on the opposed diamond anvils and the sample between them is generated using a hydraulic press. The load is then locked by rotating the body of the cell with respect to the end-nuts. The dimensions of the pressure cell have been optimized by use of finite element analysis. The cell is approximately a cylinder 7 mm long and 7 mm in diameter and weighs only 1.5 g. Due to its small size the cell thermalizes rapidly. It is capable of achieving pressures in excess of 10 GPa while allowing measurements to be performed with the maximum sensitivity of the magnetometer. The performance of the pressure cell is illustrated by a high pressure magnetic study of Mn(3)[Cr(CN)(6)](2) x xH(2)O Prussian blue analog up to 10.3 GPa.
47 citations
TL;DR: In this article, high-resolution neutron powder diffraction has been used to study the charge states and spin order in the A-site-ordered perovskite LaCu3Fe4O12.
Abstract: High resolution neutron powder diffraction has been used to study the charge states and spin order in the A-site-ordered perovskite LaCu3Fe4O12. This undergoes a first-order phase transition between cubic Im-3 structures with charge distributions LaCu3+3Fe3+4O12 and LaCu2+3Fe3.75+4O12 at TCT ≈ 400 K. Bond valence sums confirm that these charge states are adopted in the two phases, and there are no substantial valence fluctuations near the charge transfer transition. G-type antiferromagnetic order of B-site Fe3+ spins is observed in the low temperature phase LaCu3+3Fe3+4O12 and the ordered moment at 50 K is 4.0 μB. Magnetic moment is absent at the A′-site Cu3+ cation. The thermal evolution of the ordered moment enables an intrinsic TN′ ≈ 600 K to be estimated, although the actual upper limit for the spin order is TCT. No long range magnetic ordering was found in the high temperature phase, LaCu2+3Fe3.75+4O12, showing that any ordering transition for this regime has TM < TCT.
29 citations
TL;DR: A 10-layer hexagonal perovskite Ba5Sb1−xMn4+xO15−δ solid solution (0.24 ≤ x ≤ 0.36) has been synthesized by solid state reaction and studied using powder X-ray and neutron diffraction and magnetization measurements as mentioned in this paper.
Abstract: A 10-layer hexagonal perovskite Ba5Sb1−xMn4+xO15−δ solid solution (0.24 ≤ x ≤ 0.36; space group P63/mmc, a = 5.7095(1) A, and c = 23.4866(3) A for x = 0.36) has been synthesized by solid state reaction and studied using powder X-ray and neutron diffraction and magnetization measurements. This 10H polytype structure contains one corner-sharing (Sb,Mn)O6 octahedron and a tetramer of four face-sharing MnO6 octahedra per formula unit. Two magnetic transitions are observed at 129−167 K (TM) and 13−22 K (TF). The frustration index |θ|/TM, where θ is the Weiss temperature, is very close to unity, but considerable magnetic frustration is evidenced through the long-range order of a small ∼0.5 μB antiferromagnetic moment below TM, and the formation of ferro- or ferrimagnetic clusters. These freeze at TF with the |θ|/TF ≈ 7−10 index representing high magnetic frustration. TF increases directly with the excess of Mn, x, in Ba5Sb1−xMn4+xO15−δ rather than with the overall Mn content, showing that the occupation of the ...
19 citations
TL;DR: The ionic states of Cu and Mn ions and the magnetic structure in an $A$-site-ordered perovskite were investigated by powder neutron diffraction and soft x-ray absorption and magnetic circular dichroism spectroscopy experiments as discussed by the authors.
Abstract: The ionic states of Cu and Mn ions and the magnetic structure in an $A$-site-ordered perovskite ${\text{BiCu}}_{3}{\text{Mn}}_{4}{\text{O}}_{12}$ were investigated by powder neutron diffraction and soft x-ray absorption and magnetic circular dichroism spectroscopy experiments. A substitution by ${\text{Mn}}^{3+}$ was found at the square-planar ${A}^{\ensuremath{'}}$ ${\text{Cu}}^{2+}$ site, leading to a composition $\text{Bi}{(\text{Cu}^{2+}{}_{0.8}\text{Mn}^{3+}{}_{0.2})}_{3}\text{Mn}^{3.6+}{}_{4}{\text{O}}_{12}$. This compound is a ferrimagnet with a collinear spin configuration below ${T}_{\text{C}}=350\text{ }\text{K}$, and the magnetic structure is stabilized by a strong ferromagnetic coupling between the ${A}^{\ensuremath{'}}$ and $B$ site Mn ions and an antiferromagnetic coupling between Cu and Mn ions, leading to a near zero net moment at the ${A}^{\ensuremath{'}}$ site.
16 citations
TL;DR: Anion-deficient pyrochlore type oxynitrides Eu2Mo2O5−xN2+x−δ are obtained from ammonolysis of the pyrochemically deficient EuMoO7 as discussed by the authors, demonstrating that the former reaction proceeds under topochemical control.
Abstract: Anion-deficient pyrochlore type oxynitrides Eu2Mo2O5−xN2+x−δ are obtained from ammonolysis of the pyrochlore Eu2Mo2O7. However, these phases are not obtained when scheelite type EuMoO4 is used, demonstrating that the former reaction proceeds under topochemical control. This implies that other distinct new stoichiometric oxynitrides may be discovered from ammonolysis of mixed metal oxide precursors with appropriate structures.
12 citations
TL;DR: In this paper, a remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN2−x.
Abstract: A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN2−x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4−yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN2−x perovskites that show a wide range of compositions −0.16 ≤ x ≤ 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2−x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = −0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified.
9 citations
Patent•
24 Jun 2010TL;DR: In this paper, a perovskite-type composite oxide containing palladium is used as the catalyst for synthesis reaction in the Sonogashira reaction represented by the following reaction scheme.
Abstract: To provide a catalyst for synthesis reaction which can achieve good yield in the Sonogashira reaction and also can be recovered after the reaction, and a method for synthesizing a compound in which the catalyst for synthesis reaction is used, a perovskite-type composite oxide containing palladium is used as the catalyst for synthesis reaction in the Sonogashira reaction represented by the following reaction scheme (1): R1—X+HC≡CR2→R1C≡CR2 (1)
5 citations
TL;DR: In the last 25 years, seven distinct families of superconductors with critical temperatures at ambient pressure that equal or surpass the historic 23 K limit for Nb3Ge have been discovered.
Abstract: Seven distinct families of superconductors with critical temperatures at ambient pressure that equal or surpass the historic 23 K limit for Nb3Ge have been discovered in the last 25 years. Each family is reviewed briefly and their common chemical features are discussed. High temperature superconductors are distinguished by having a high (\geq 50%) content of nonmetallic elements and fall into two broad classes. 'Metal-nonmetal' superconductors require a specific combination of elements such as Cu-O and Fe-As which give rise to the highest known Tc's, probably through a magnetic pairing mechanism. 'Nonmetal-bonded' materials contain covalently-bonded nonmetal anion networks and are BCS-like superconductors. Fitting an extreme value function to the distribution of Tc values for the known high-Tc families suggests that the probability of a newly discovered superconductor family having maximum Tc > 100 K is ~0.1-1%, decreasing to ~0.02-0.2% for room temperature superconductivity.
4 citations
TL;DR: Eu2Mo2O7 (I) is synthesized from a stoichiometric mixture of Eu2O3, MoO2, and Mo (alumina boat, flowing Ar, 1450 °C, 14 h) and EuMoO4 (II) as discussed by the authors.
Abstract: Eu2Mo2O7 (I) is synthesized from a stoichiometric mixture of Eu2O3, MoO2, and Mo (alumina boat, flowing Ar, 1450 °C, 14 h) and EuMoO4 (II) from a stoichiometric mixture of Eu2O3, MoO3, and Mo (quartz tube, 600 °C, 24 h, and 1050 °C, 36 h).
TL;DR: Resistivity and powder X-ray diffraction measurements show that the suppression of Au(+)/Au(3+) charge order results in a non-metallic phase containing localised Au(2+) states that is irreversibly amorphised above 120 kbar, and a gradual metallisation observed above 175 kbar may result from decomposition within the amorphous material.