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Structural investigation of Nb-based layer sulfides
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work we have investigated the intercalation of electron-donors between NbS2 slabs in Nb-based layer sulfides.

Two series of Sr substituted Nb-based misfit sulfides belonging to the 1.5Q/1H and 1Q/1H series of misfit layer compounds have been synthesised. For large lanthanides (Ln=La, Ce), only the 1Q/1H compounds formed whereas for smaller lanthanides and yttrium, both types of phases can be obtained. The crystal structure of misfit sulfide (Pr0.55Sr0.45S)1.15NbS2 has been refined using the composite approach. In the Q-slab, Pr-atoms are partly replaced by Sr with a random distribution over one cation position. The crystal structure of misfit sulfide [(Sm1/3Sr2/3S)1.5]1.15NbS2 belonging to the 1.5Q/1H series have also been determined. The obtained results suggest a preferred occupancy of the cation positions in the slab where Sr atoms mainly occupy positions on the exterior of the slab while Sm atoms are in the center of the slab. The (La1-xSrxS)1.15NbS2 solid solution (0.1<x<0.9) has also been studied. It was found that the maximum value of Sr substitution is 40-50% and therefore, the minimal value of charge transfer to stabilize this structure type is about 0.6ē per Nb atom.

An attempt to synthesize SrxNbS2 (0.1≤x≤0.5) intercalates was made but single phases were not obtained and increasing the temperature from 1000оС to 1100оС leads to the decomposition of these intercalates. Single crystals of Sr0.22Nb1.05S2 and Sr0.23NbS2 were found and their structures were determined. The structures belong to two different types of packings with statistical distribution of Sr between layers.

A new superconducting sulfide, "EuNb2S5", was investigated by ED and HREM and its structure model consisting of Nb7S14 and (Eu3S4)2 slabs alternating along the c-axis is suggested. An attempt to suggest a model for the structure of "SrNb2S5" by means of X-ray single crystal diffraction was made. The proposed structure consists of two types of slabs: a Nb7S14 and a [Sr6(NbS4)2S] slab with niobium in tetrahedral coordination. It is shown that "SrNb2S5" and "EuNb2S5" are have similar structures.

For the first time, single crystals of the complex sulfide BaNb0.9S3 have also been studied by means of X-ray single crystal diffraction. The single crystal refinement and EDX analysis showed the existence of cation vacancies at the niobium position. BaNb0.9S3 has also been studied by ED and no superstructure was found which implies that and the vacancies are statistically distributed.

No improvement of the magnetic properties of the studied compounds was observed in comparison to NbS2.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi , 2004. , 116 p.
Keyword [en]
Nb-based sulfides, misfit layered, structure determination, electron diffraction
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-177ISBN: 91-7265-899-1 (print)OAI: oai:DiVA.org:su-177DiVA: diva2:190551
Public defence
2004-06-10, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00
Opponent
Supervisors
Available from: 2004-05-19 Created: 2004-05-19Bibliographically approved
List of papers
1. A new superconducting sulfide—'EuNb2S5'
Open this publication in new window or tab >>A new superconducting sulfide—'EuNb2S5'
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1998 (English)In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 300, 67-70 p.Article in journal (Refereed) Published
Abstract [en]

A new low-temperature superconducting (Tc≈3 K) niobium sulfide ‘EuNb2S5' with a hexagonal structure (a=3.3556(8) Å, c=23.440(9) Å) was synthesized from a mixture of EuS, Nb(m) and S in evacuated and sealed silica tubes, heated at 1100°C for 48 h. This superconductor was characterized by EDX analysis, X-ray powder and electron diffraction studies. Electron diffraction revealed the presence of a supercell: asuper=bsuper=√7×a.

Place, publisher, year, edition, pages
Elsewier, 1998
Keyword
Superconductivity, Synthesis, Eu- and Nb-based sulfide
National Category
Chemical Sciences
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-23184 (URN)10.1016/S0921-4534(98)00065-3 (DOI)
Note
Part of urn:nbn:se:su:diva-177Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2017-12-13Bibliographically approved
2. Crystal Structure of BaNb0.9S3
Open this publication in new window or tab >>Crystal Structure of BaNb0.9S3
2001 (English)In: Crystallography Reports, ISSN 1063-7745, Vol. 46, no 3, 373-376 p.Article in journal (Refereed) Published
Abstract [en]

Single crystals of the composition BaNb[sub 0.9]S[sub 3] have been synthesized from the BaS, Nb, and S mixture and the BaCl[sub 2] flux at 900°C. The BaNb[sub 0.9]S[sub 3] structure was refined by X-ray single-crystal and electron diffraction data. The compound is crystallized in the sp. gr P6[sub 3]/mmc (z = 2) with the unit-cell parameters a = 6.839(1) Å and c = 5.745(1) Å. It was established that the cationic vacancies in the niobium positions are statistically distributed over the structure.

Place, publisher, year, edition, pages
American Institute of Physics, 2001
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-23185 (URN)
Note
Part of urn:nbn:se:su:diva-177Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2009-12-30Bibliographically approved
3. A New Structure Type of the Ternary Sulfide Eu1.3Nb1.9S5
Open this publication in new window or tab >>A New Structure Type of the Ternary Sulfide Eu1.3Nb1.9S5
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2002 (English)In: Journal of Solid State Chemistry, ISSN 1095-726X, Vol. 164, no 2, 345-353 p.Article in journal (Refereed) Published
Abstract [en]

The structure model for the Eu1.3Nb1.9S5 compound is determined based on high-resolution electron microscopy evidence. This compound crystallizes in a hexagonal unit cell with a=8.8732(8) Å and c=23.45(1) Å. Its structure is built up as an alternating sequence of trigonal-prismatic NbS2 layers of formula [Nb7S14] and [Nb(Eu3S4)2] slabs along the c-direction. In the [Nb(Eu3S4)2] block the stacking of two close-packed (Eu3S4) layers creates octahedral interstices formed by S atoms; these cavities are occupied by Nb cations. The model is compared with structures of other Eu-containing niobium sulfides, such as Eu0.167NbS2 and the misfit compound [(EuS)1.5]1.15NbS2.

Place, publisher, year, edition, pages
Elsevier, 2002
National Category
Physical Chemistry
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-23186 (URN)10.1006/jssc.2001.9501 (DOI)
Note
Part of urn:nbn:se:su:diva-177Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2009-12-30Bibliographically approved
4. New strontium and rare earth-based mixed niobium misfit sulfides
Open this publication in new window or tab >>New strontium and rare earth-based mixed niobium misfit sulfides
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2003 (English)In: Solid State Sciences, Vol. 5, no 3, 495-502 p.Article in journal (Refereed) Published
Abstract [en]

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 1000 °C for 144 h under a sulfur partial pressure of 49.3 kPa. The compounds have been characterized by EDX analysis, X-ray single crystal and powder diffraction, electron diffraction, and magnetic susceptibility measurements. Both sulfides have misfit structures with orthorhombic symmetry for the (Ln1/3Sr2/3S)1.5 (Ln=Sm, Tb) and NbS2 subsystems. The lattice parameters for the different subsystems are: for the Sm-based sulfide [(Sm1/3Sr2/3S)1.5]: a=5.7953(9) Å, b=5.8007(5) Å, c=14.957(2) Å and [NbS2]: a=3.3420(7) Å, b=5.8008(5) Å, c=14.955(2) Å, and for the Tb-based sulfide [(Tb1/3Sr2/3S)1.5]: a=5.769(2) Å, b=5.7766(7) Å, c=14.906(2) Å and [NbS2]: a=3.340(1) Å, b=5.7769(8) Å, c=14.905(2) Å. The [(Sm1/3Sr2/3S)1.5]1.15NbS2 crystal structure has been refined from X-ray single crystal data. It belongs to the 1.5Q/1H homologue type where the (Sm1/3Sr2/3S)1.5 part is a three-atoms-thick slab. Sr-cations are mainly located at the exterior of the slab whereas Sm preferably occupy the positions at its center. Both compounds exhibit paramagnetic temperature dependence down to 2 K.

Place, publisher, year, edition, pages
Elsevier, 2003
National Category
Physical Chemistry
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-23187 (URN)10.1016/S1293-2558(03)00023-2 (DOI)
Note
Part of urn:nbn:se:su:diva-177Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2009-12-30Bibliographically approved
5. Synthesis and study of Sr-substituted misfit layer sulfides
Open this publication in new window or tab >>Synthesis and study of Sr-substituted misfit layer sulfides
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2005 (English)In: Materials Research Bulletin, ISSN 0025-5408, Vol. 40, no 1, 79-91 p.Article in journal (Refereed) Published
Abstract [en]

Two series of [(Ln1/3Sr2/3S)1.5]1.15NbS2 (1.5Q/1H) and (Ln1−xSrxS)1+yNbS2 (1Q/1H) misfit layer sulfides have been synthesised and studied by X-ray powder and single crystal diffraction, EDX-analysis and magnetic measurements. For the early lanthanides (Ln = La, Ce) only the (Ln1−xSrxS)1+yNbS2 (x < 0.40–0.45, y = 0.15–0.17) compounds were formed whereas for late lanthanides (Ln = Pr, Nd, Sm, Gd–Er, Yb, Lu), and yttrium, both types of phases can be obtained. The crystal structure of (Pr0.55Sr0.45S)1.15NbS2 has been refined on the basis of X-ray single crystal data using the superspace approach. It consists of double layers [Pr0.55Sr0.45S] of NaCl-type (Q-part: a = 5.799(3) Å, b = 5.810(2) Å, c = 23.331(9) Å, z = 4) and NbS2-sandwiches (H-part: a = 3.332(3) Å), z = 8, yielding a q-vector q = (α 0 0), α = 0.74) alternating along the c-direction. The superspace group pair is Fm2m (α 0 0):Fm2m (α 0 0) (No. 42.7). The refinement converged to Rw(obs) = 0.069. According to the structure refinement and EDX-analysis data in the [Pr0.55Sr0.45S]-slab almost half of the Pr-atoms are randomly replaced by Sr. The minimal formal value of charge transfer from the Q- to the H-part of the structure necessary to stabilise the misfit Nb-based layer sulfides has been estimated as about 0.6 ē per Nb atom.

Place, publisher, year, edition, pages
Elsevier, 2005
National Category
Physical Chemistry
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-23188 (URN)10.1016/j.materresbull.2004.09.017 (DOI)
Note
Part of urn:nbn:se:su:diva-177Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2009-12-30Bibliographically approved

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