Incommensurately Modulated Cu_0.9Pb_1.2Sb_2.9Se₆ in the Lillianite Structure Type.

Area of Science:

• Solid State Chemistry
• Materials Science
• Crystallography

Background:

• Investigating novel thermoelectric materials is crucial for energy harvesting.
• Lillianite-type structures are known for their potential thermoelectric properties.
• Understanding structure-property relationships in complex chalcogenides is key.

Purpose of the Study:

• To characterize the crystal structure of Cu$_{0.9}$Pb$_{1.2}$Sb$_{2.9}$Se$_{6}$ at room temperature.
• To investigate the phase transition and structural changes at elevated temperatures.
• To evaluate the thermoelectric properties of the synthesized material.

Main Methods:

• Single crystal X-ray diffraction with synchrotron radiation for detailed structure refinement.
• Superspace group analysis to describe the incommensurately modulated structure.
• High-resolution transmission electron microscopy (HRTEM) for structural corroboration.
• Transport property measurements to determine thermoelectric performance.

Main Results:

• A phase with an incommensurately modulated lillianite-type structure (superspace group *Cmcm*(α00)00*s*) was identified.
• Positional and occupational modulations involving Sb and Cu atoms were observed.
• A reversible phase transition occurred above 523 K, leading to increased disorder.
• The material exhibits p-type semiconductor behavior with a thermoelectric figure of merit (*zT*) up to 0.1 at 623 K.

Conclusions:

• The complex modulated structure influences the thermoelectric properties.
• The observed phase transition affects lattice parameters and physical properties.
• Small substitutions could potentially optimize carrier concentration and enhance thermoelectric efficiency (*zT*).