3 years ago

Tl2Ag12Se7: A New pnp Conduction Switching Material with Extraordinarily Low Thermal Conductivity

Tl2Ag12Se7: A New pnp Conduction Switching Material with Extraordinarily Low Thermal Conductivity
Holger Kleinke, Cheriyedath Raj Sankar, Yixuan Shi, Abdeljalil Assoud
While continuing our investigations of thallium chalcogenides because of their outstanding thermoelectric properties, we discovered a new selenide with an interesting pnp switching behavior around 400 K. Tl2Ag12Se7 was prepared via high temperature reaction from the elements in the stoichiometric ratio. This selenide crystallizes in a new structure type, namely a √3 × √3 × 1 super cell of the Zr2Fe12P7 type, adopting space group P3̅, a = b = 18.9153(18) Å, c = 4.3783(4) Å, and V = 1356.6(2) Å3 (Z = 3). The structure consists of a complex network of three-dimensionally connected AgSe4 tetrahedra that include linear channels filled with thallium atoms. This material is a semiconductor with an experimentally derived activation gap of 0.8 eV and extraordinarily low thermal conductivity of <0.45 W m–1 K–1. A reversible phase transition causes a pnp switch from p-type to n-type and back to p-type conduction beginning around 390 K, with the thermopower changing fast from +230 μV K–1 at 390 K to −230 μV K–1 at 410 K, and then back up to +75 μV K–1 at 420 K.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b04015

DOI: 10.1021/acs.chemmater.7b04015

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