<p>In this work we have investigated the intercalation of electron-donors between NbS<sub>2</sub> slabs in Nb-based layer sulfides.</p><p>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 (Pr<sub>0.55</sub>Sr<sub>0.45</sub>S)<sub>1.15</sub>NbS<sub>2</sub> 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 [(Sm<sub>1/3</sub>Sr<sub>2/3</sub>S)<sub>1.5</sub>]<sub>1.15</sub>NbS<sub>2</sub> 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 (La<sub>1-x</sub>Sr<sub>x</sub>S)<sub>1.15</sub>NbS<sub>2</sub> 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. </p><p>An attempt to synthesize Sr<sub>x</sub>NbS<sub>2</sub> (0.1≤x≤0.5) intercalates was made but single phases were not obtained and increasing the temperature from 1000<sup>о</sup>С to 1100<sup>о</sup>С leads to the decomposition of these intercalates. Single crystals of Sr<sub>0.22</sub>Nb<sub>1.05</sub>S<sub>2</sub> and Sr<sub>0.23</sub>NbS<sub>2</sub> were found and their structures were determined. The structures belong to two different types of packings with statistical distribution of Sr between layers.</p><p>A new superconducting sulfide, "EuNb<sub>2</sub>S<sub>5</sub>", was investigated by ED and HREM and its structure model consisting of Nb<sub>7</sub>S<sub>14</sub> and (Eu<sub>3</sub>S<sub>4</sub>)<sub>2</sub> slabs alternating along the c-axis is suggested. An attempt to suggest a model for the structure of "SrNb<sub>2</sub>S<sub>5</sub>" by means of X-ray single crystal diffraction was made. The proposed structure consists of two types of slabs: a Nb<sub>7</sub>S<sub>14</sub> and a [Sr<sub>6</sub>(NbS<sub>4</sub>)<sub>2</sub>S] slab with niobium in tetrahedral coordination. It is shown that "SrNb<sub>2</sub>S<sub>5</sub>" and "EuNb<sub>2</sub>S<sub>5</sub>" are have similar structures.</p><p>For the first time, single crystals of the complex sulfide BaNb<sub>0.9</sub>S<sub>3</sub> 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. BaNb<sub>0.9</sub>S<sub>3</sub> has also been studied by ED and no superstructure was found which implies that and the vacancies are statistically distributed.</p><p>No improvement of the magnetic properties of the studied compounds was observed in comparison to NbS<sub>2</sub>.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-177 |
| Date | January 2004 |
| Creators | Grippa, Alexander |
| Publisher | Stockholm University, Department of Physical, Inorganic and Structural Chemistry, Stockholm : Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
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