Dataset Information

Effect of the Order-Disorder Transition on the Seebeck Coefficient of Nanostructured Thermoelectric Cu₂ZnSnS₄.

ABSTRACT: Bulk samples of kesterite (Cu₂ZnSnS₄, CZTS) were produced by cold-pressing and sintering of CZTS powders obtained via reactive ball-milling. An increase in the Seebeck coefficient of more than 100 ?V/K, almost doubling the expected value, is noticed around a temperature of 260 °C. As pointed out by thermal analyses, this is due to a second order transition of kesterite from an ordered I-4 to a disordered I-42m crystal structure. Conversely to what happens for solar cell materials, where the transition is considered to be detrimental for the performance, it appears to be beneficial for the thermoelectric Seebeck coefficient, suggesting that higher crystal symmetry and cation-disorder due to the transition lead to thermopower enhancement.

SUBMITTER: Isotta E

PROVIDER: S-EPMC6567239 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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Publications

Effect of the Order-Disorder Transition on the Seebeck Coefficient of Nanostructured Thermoelectric Cu2ZnSnS4.

Isotta Eleonora E Fanciulli Carlo C Pugno Nicola M NM Scardi Paolo P

Nanomaterials (Basel, Switzerland) 20190517 5

Bulk samples of kesterite (Cu2ZnSnS4, CZTS) were produced by cold-pressing and sintering of CZTS powders obtained via reactive ball-milling. An increase in the Seebeck coefficient of more than 100 μV/K, almost doubling the expected value, is noticed around a temperature of 260 °C. As pointed out by thermal analyses, this is due to a second order transition of kesterite from an ordered I-4 to a disordered I-42m crystal structure. Conversely to what happens for solar cell mat ...[more]

PMID: 31108991

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Project description:Copper and silver based chalcogenides, chalco-halides, and halides form a unique class of semiconductors, as they display mixed ionic and electronic conduction in their superionic phase. These compounds are composed of softly coupled cationic and anionic substructures, and undergo a transition to a superionic phase displaying changes in the substructure of their mobile ions with varying temperature. Here, we demonstrate a facile, ambient and capping agent free solution based synthesis of AgCuS nanocrystals and their temperature dependent (300-550 K) thermoelectric properties. AgCuS is known to show fascinating p-n-p type conduction switching in its bulk polycrystalline form. Temperature dependent synchrotron powder X-ray diffraction, heat capacity and Raman spectroscopy measurements indicate the observation of two superionic phase transitions, from a room temperature ordered orthorhombic (β) to a partially disordered hexagonal (α) phase at ∼365 K and from the hexagonal (α) to a fully disordered cubic (δ) phase at ∼439 K, in nanocrystalline AgCuS. The size reduction to the nanoscale resulted in a large variation in the thermoelectric properties compared to its bulk counterpart. Temperature dependent Seebeck coefficient measurements indicate that the nanocrystalline AgCuS does not display the p-n-p type conduction switching property like its bulk form, but remains p-type throughout the measured temperature range due to the presence of excess localized Ag vacancies. Nanocrystalline AgCuS exhibits a wider electronic band gap (∼1.2 eV) compared to that of the bulk AgCuS (∼0.9 eV), which is not sufficient to close the band gap to form a semimetallic intermediate state during the orthorhombic to hexagonal superionic phase transition, thus AgCuS nanocrystals do not show conduction type switching properties like their bulk counterpart. The present study demonstrates that ambient solution phase synthesis and size reduction to the nanoscale can tailor the order-disorder phase transition, the band gap and the electronic conduction properties in superionic compounds, which will not only enrich solid-state inorganic chemistry but also open a new avenue to design multifunctional materials.

Dataset Information

Effect of the Order-Disorder Transition on the Seebeck Coefficient of Nanostructured Thermoelectric Cu₂ZnSnS₄.

Publications

Effect of the Order-Disorder Transition on the Seebeck Coefficient of Nanostructured Thermoelectric Cu<sub>2</sub>ZnSnS<sub>4</sub>.

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