ZfN: Search Results

1	Author	Carla Cannas, Giorgio Concas, Anna Musinu, Giorgio Piccaluga, Giorgio Spano	Requires cookie*
	Title	Mössbauer Spectroscopic Study of Fe 2 0 3 Nanoparticles Dispersed over a Silica Matrix
	Abstract	A series of Fe 2 0 3 -Si02 nanocomposites (9 -33 wt% of Fe 2 0 3) has been prepared by a sol-gel method and submitted to thermal treatments at 300 -900 °C. The samples were characterized by X-ray diffraction and Mössbauer Spectroscopy measurements. Superparamagnetic behavior is exhibited by all the samples, indicating that the size of iron oxide grains is in the nanometer range (4-6 nm). Increase of iron content and temperature treatment give rise to a small particle growth, while the spread of sizes around the average value increases with the iron concentration. The Mössbauer spectra, at all the explored compositions, show a very steep increase of the peak width by treatment temperature at 900 °C, indicating the formation of the ferrimagnetic 7-Fe 2 0 3 phase from the antiferromagnetic amorphous Fe 2 0 3 phase, which dominates in the samples treated at lower temperatures. The samples at 28.5% and 33.2%, treated at 900 °C, also show a component of 7-Fe 2 0 3 in the blocked state at room temperature. Moreover, the growth of the particles favours the formation of other oxide phases (a and £ phase) along with the 7 phase.
	Reference	Z. Naturforsch. 54a, 513—518 (1999); received June 28 1999
	Published	1999
	Keywords	Nanocomposite, Ferric Oxide, Mössbauer Spectroscopy, X-ray Diffraction
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	TEI-XML for	default:Reihe_A/54/ZNA-1999-54a-0513.pdf
	Identifier	ZNA-1999-54a-0513
	Volume	54

2	Author	Rolf-Dieter Hoffmann3, Dirk Kußmanna, Ute Ch, Rainer Rodewald3, Pöttgen3, Carsten Rosenhahnb, BerndD. Moselb	Requires cookie*
	Title	New Stannides CaTSn2 (T = Rh, Pd, Ir) and Ca2Pt3 Sn5 -Synthesis, Structure and Chemical Bonding
	Abstract	New stannides CaTSm (T = Rh, Pd, Ir) and Ca2P hSn5 were prepared as single phase materials by a reaction o f the elements in glassy carbon crucibles under flowing purified argon. The four compounds were investigated by X-ray diffraction both on powders and single crystals and their structures were refined from single crystal data. The stannides CaTSn2 (T = Rh, Pd, Ir) adopt
	Reference	Z. Naturforsch. 54b, 709 (1999); received February 25 1999
	Published	1999
	Keywords	Intermetallic Calcium Compounds, Crystal Structure, Mössbauer Spectroscopy, Chemical Bonding
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	TEI-XML for	default:Reihe_B/54/ZNB-1999-54b-0709.pdf
	Identifier	ZNB-1999-54b-0709
	Volume	54

3	Author	Dirk Kußmann3, Rainer Pöttgen, Ute Ch, Carsten Rodewald3, BerndD. Rosenhahnb, Gunter Moselb, Bernd Kotzyba3, Künnen3	Requires cookie*
	Title	Structure and Properties of the Stannide Eu2Au2Sn5, and its Relationship with the Family of BaAl4-Related Structures
	Abstract	The stannide Eu2Au2Sn.i was prepared by high-frequency melting of the elements in a sealed tantalum tube. The structure of Eu-iAu^Sn^ was refined from single crystal X-ray data: P2\/m, a = 928.6(2), b = 465.8(2), c = 1042.9(3) pm, ß = 92.28(2)°, wR2 = 0.0653, 1220 F2 values and 56 variables. The structure of Eu2Au2Sns is of a new type, it can be considered as an ordered defect variant of the BaAU type. Due to the ordered defects, the coordination number (CN) of the two crystallographically different europium sites is reduced from CN 16 to CN 14. The gold and tin atoms in Eu2Au2Sn_s form a complex three-dimensional [A ^Sns] polyanion in which the europium atoms are embedded. Within the polyanion short Au-Sn and Sn-Sn distances are indicative of strongly bonding Au-Sn and Sn-Sn interactions. A detailed group-subgroup scheme for various ordered and defect variants of the BaAU family is presented. EuiA^Sn? shows Curie-Weiss behavior above 50 K with an experimental magnetic moment of 7.90(5) /ub/Eu, indicating divalent europium. Antiferromagnetic ordering is detected at 5.8(5) K at low fields and a metamagnetic transition occurs at a critical field of 1.4(2) T. Eu2Au2Sns is a metal with a specific resistivity of 150±20 p f i cm at room temperature. The results of l:i\|Eu and 119Sn Mössbauer spectroscopic experiments are compatible with divalent europium and show complex hyperfine field splitting with a transferred magnetic hyperfine field at the tin nuclei at low temperature.
	Reference	Z. Naturforsch. 54b, 1155—1164 (1999); received June 7 1999
	Published	1999
	Keywords	Europium Gold Stannide, Crystal Structure, Mössbauer Spectroscopy, Group-Subgroup Relations
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	TEI-XML for	default:Reihe_B/54/ZNB-1999-54b-1155.pdf
	Identifier	ZNB-1999-54b-1155
	Volume	54