Roland Tellgren

Bio: Roland Tellgren is an academic researcher from Uppsala University. The author has contributed to research in topics: Neutron diffraction & Magnetic structure. The author has an hindex of 25, co-authored 119 publications receiving 1788 citations.

Investigation of the structure of the relaxor ferroelectric Pb(Fe1/2Nb1/2)O3 by neutron powder diffraction

Abstract: The complex perovskite lead iron niobate, Pb(Fe1/2 Nb1/2 )O3 (PFN), has been studied by neutron powder diffraction Following collection of diffraction data at 300 K and at 10 K, structural refinements have been carried out by means of the Rietveld method As expected, a straightforward unit cell of symmetry R 3m was obtained for the 300 K structure, with the same symmetry and a similar unit cell also obtained at low temperature Furthermore, in order to obtain a good agreement with experiment at 10 K, it was necessary to assign non-zero magnetic moments to the iron ions, these being in a collinear, antiferromagnetic alignment This magnetic structure can be described with reference to doubled unit cell axes The factors governing the observed structures of PFN are discussed by comparison with the related system of Pb(Mg1/3 Nb2/3 )O3

Ion Exchange in Manganese Dioxide Spinel: Proton, Deuteron, and Lithium Sites Determined from Neutron Powder Diffraction Data

Abstract: The structures of deuterated, protonated, and relithiated forms of MnO2 spinel, obtained by ion exchange of Li ions with D or H in a well-crystallized spinel Li1.27Mn1.73O4 compound, have been determined by powder neutron diffraction. Refinements were carried out using the Rietveld method of powder profile analysis in the space group Fd3m. Li ions are removed from both tetrahedral 8a and octahedral 16d sites when Li1.27Mn1.73O4 is contacted with DCl or HCl solution. The neutron diffraction data show that deuterium and hydrogen ions are predominantly incorporated into the crystal as −OD and −OH by bonding to lattice oxygen atoms without any other major change to the MnO2 spinel structure. The −OD and −OH groups are directed into the interstitial space of the 8a tetrahedra, but with an orientation which suggests that the deuteron or proton site is favored for occupation only when the nearest neighbor octahedral 16d site contains no Mn ion. When the protonated compound is contacted with LiOH solution, reinse...

Hydrogen and deuterium in transition metal-p element compounds: Crystal chemical aspects of interstitial solid solubility and hydride phase formation

Abstract: Compounds of transition metals with p elements of groups IIIb–VIIb which have been reported to exhibit hydrogen-absorbing properties are surveyed. Hydrogen is taken up only by those materials that have metallic properties or contain metal clusters with delocalized bonding. Almost all p elements can be constituents of these materials, and at least one transition metal component which is itself capable of dissolving hydrogen or forming hydride phases must be present. The crystallography of the hydride phases is presented and discussed with particular emphasis on results obtained by neutron diffraction methods. The hydrogen atoms are accommodated either in interstitial solid solutions with only minor changes in the host lattices or in new phases formed by major rearrangements of both transition metal and p element atoms. The distribution of the hydrogen atoms on the interstitial sites in the structures appears to be governed by two empirical rules: the hydrogen atoms are always more than 2 A apart and they preferentially occupy those sites that are most distant from the p element atoms.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Recent progress in relaxor ferroelectrics with perovskite structure

Abstract: Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Nitrile-Containing Pharmaceuticals: Efficacious Roles of the Nitrile Pharmacophore

Abstract: Fraser F. Fleming,* Lihua Yao, P. C. Ravikumar, Lee Funk, and Brian C. Shook Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530, Mylan Pharmaceuticals Inc., 781 Chestnut Ridge Road, Morgantown, West Virginia 26505, and Johnson & Johnson Pharmaceutical Research and Development, L.L.C., Welsh and McKean Roads, P.O. Box 776, Spring House, Pennsylvania 19477

Polyanionic (phosphates, silicates, sulfates) frameworks as electrode materials for rechargeable Li (or Na) batteries.

Abstract: For more than 20 years, most of the technological achievements for the realization of positive electrodes for practical rechargeable Li battery systems have been devoted to transition metal oxides such as LixMO2 (M = Co, Ni, Mn), LixMn2O4, LixV2O5, or LixV3O8. The first two classes of materials built on close-packed oxygen stacking adopt bidimensional and tridimensional crystal structures, respectively (Figure 1), from which lithium ions may be easily intercalated or extracted in a reversible manner. These oxides are reasonably good ionic and electronic conductors, and lithium insertion/extraction proceeds while operating on the M4+/M3+ redox couple, located between 4 and 5 V versus Li+/Li...