Ultra-low thermal conductivity of Tl0.98In5Se8 and structure of the new complex chalcogenide Tl0.98In13.12Se16.7Te2.3
Résumé
TlIn5Se8 has been synthesized by means of solid-state reaction and densified by Spark Plasma Sintering. The compound is a semiconductor with a band gap of 1.62 eV estimated from reflectance measurements. Its thermal conductivity is about 0.45 W m(-1). K-1 in the temperature range 300-673 K, an extremely low value attributed to its complex pseudo-1D structure reminiscent of the pseudo-hollandite. While attempting to dope TlIn5Se8 with Te, a new complex chalcogenide was discovered and characterized by the combination of TEM and XRD diffraction. It belongs to the A(2)In(12)X(19) family, crystallizing in the R (3) over bar H space group. Single crystal X-ray diffraction study led to a refined composition of Tl0.98In13.12Se16.7Te2.3 with cell parameters a=13.839(5) angstrom and c=35.18(3) angstrom. A static disorder is found on one indium site situated in an octahedral environment. The single crystal XRD study is in agreement with TEM analyses in STEM-HAADF image mode that do not show any extended defects or disorder at atomic scale.