Ba4Cd2Ge2Te9: A Promising Infrared Functional Crystal with Large Birefringent and Photoluminescence Properties

Abstract

Herein, a new Cd-based telluride Ba4Cd2Ge2Te9 was successfully synthesized and characterized, which was first identified in the Ba-Cd-Ge-Te system. It crystallizes in the Pbcm space group and its structure features infinite [Cd2Ge2Te9]8- chains, with Ba2+ filling in the interstitial space to balance the charge. The fluorescence spectrum indicates that the title compound generates purple-emission the range of 415-459nm under the 300nm excitation, with a peak lifetime of about 1.18ns at 436nm. In addition, first-principles calculations show that Ba4Cd2Ge2Te9 has a birefringence of 0.298@2090nm, which is determined by the superposition of the polarization of the terminal Te atom and Ge2Te6 unit. Thermoelectricity measurements show that the title compound possesses a large Seebeck coefficient (655 μV K−1 @300K) and a low thermal conductivity (0.87Wm-1 K-1 @300K).