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Metastable Cd4Sb3: A Complex Structured Intermetallic Compound with Semiconductor Properties
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
Department of Chemistry and Biochemistry, Arizona State University.
School of Materials, Arizona State University.
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2009 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 46, 15564-15572 p.Article in journal (Refereed) Published
Abstract [en]

The metastable binary intermetallic compound Cd4Sb3 was obtained as polycrystalline ingot by quenching stoichiometric Cd-Sb melts and as mm-sized crystals by employing Bi or Sn fluxes. The compound crystallizes in the monoclinic space group Pn with a = 11.4975(5) Å, b = 26.126(1) Å, c = 26.122(1) Å, b = 100.77(1)o and V = 7708.2(5) Å3. The actual formula unit of Cd4Sb3 is Cd13Sb10 and the unit cell contains 156 Cd and 120 Sb atoms (Z = 12). Cd4Sb3 displays a reversible order-disorder transition at 373 K and decomposes exothermically into a mixture of elemental Cd and CdSb at around 520 K. Disordered β-Cd4Sb3 is rhombohedral (space group R-3c, a ≈ 13.04 Å, c ≈ 13.03 Å) with a framework isostructural to β-Zn4Sb3. The structure of monoclinic α-Cd4Sb3 bears resemblance to the low-temperature modifications of Zn4Sb3, α- and α’-Zn4Sb3, in that randomly distributed vacancies and interstitial atoms of the high-temperature modification aggregate and order into distinct arrays. However, the nature of aggregation and distribution of aggregates is different in the two systems. Cd4Sb3 displays the properties of a narrow gap semiconductor. Between 10 and 350 K the resistivity of melt-quenched samples first increases with increasing temperature until a maximum value at 250 K and then decreases again. The resistivity maximum is accompanied with a discontinuity in the thermopower, which is positive and increasing from 10 to 350 K. The room temperature values of the resistivity and thermopower are about 25 mWcm and 160 mV/K, respectively. Flux synthesized samples show altered properties due to the incorporation of small amounts of Bi or Sn (less than 1 at. %). Thermopower and resistivity appear drastically increased for Sn doped samples. Characteristic for Cd4Sb3 samples is their low thermal conductivity, which drops below 1 W/mK above 130 K and attains values around 0.75 W/mK at room temperature, which is comparable to vitreous materials.

Place, publisher, year, edition, pages
Washington, DC: American Chemical Society , 2009. Vol. 130, no 46, 15564-15572 p.
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-42922OAI: oai:DiVA.org:su-42922DiVA: diva2:352237
Available from: 2010-09-21 Created: 2010-09-20 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Thermoelectric Properties of Antimony Based Networks
Open this publication in new window or tab >>Thermoelectric Properties of Antimony Based Networks
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the retreating sources of carbon based fuels, thermoelectric materials can play an important role in the future of environmentally friendly power generators. Sb based framework have in some cases shown some promising properties as thermoelectric materials. The physical properties may be modified with doping or incorporation of new elements. Zn4Sb3 and Cd4Sb3 are structurally related with a Sb-based network and Zn/Cd occupying the rest of the positions. Both structures undergo order-disorder αβ transition of the Zn/Cd positions, at 254 K and ~355 K respectively. The previously ordered interstitial atoms become distributed in the structure and the two high temperature phases are isostructural (R-3c). Cd4Sb3 was synthesized from melt-quench, flux synthesis with Sn, Bi and In. The syntheses made with In resulted in interstitial-free β-Cd4Sb3 with the composition Cd11.7In1.5Sb10. This compound exhibits no phase transitions until decomposition. ZnSnSb2 and InSb both exhibit the cubic sphalerite structure. ZnSnSb2 is metallic and InSb narrow band-gap semiconductor. Attempts were made to fine-tune the electrical properties by probing the mutual solid solubility range. The formula [ZnSnSb2]x[2(InSb)]1-xSn4 and 0<X<1 with 0.1 increments for the whole composition range was used. Resistivity changes from semiconducting to metallic conduction between x=0.9 and x=0.8. In the attempt to dope Zn4Sb3 by In a novel metastable compound with the composition Zn9Sb6In2 was found. Another novel phase was discovered with the composition Zn5Sb4In2-δ (δ=0.15).  The two phases have the same Sb-framework with a CuAl2 structure. Zn and In arrangements fill the square antiprisms formed by the stacking of 32434 nets in anti configuration. The filling of the antiprisms in the two phases are different, in Zn9Sb6In2 the antiprisms have two filling arrangements, an In or Zn3 triangles. In Zn5Sb4In2-δ the antiprisms are filled with an In and a Zn that occupies a split position to form a hetero-atomic dimers.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2010. 65 p.
Keyword
thermoelectric, narrow gap semiconductors, zinc antimonides, cadmium antimonides, chalcopyrites, sphalerites
National Category
Inorganic Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-42981 (URN)978-91-7447-143-4 (ISBN)
Public defence
2010-10-22, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
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Available from: 2010-09-30 Created: 2010-09-22 Last updated: 2010-10-04Bibliographically approved

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