Ba4Cd2Ge2Te9: A promising infrared functional crystal with large birefringent and photoluminescence properties

Herein, a new Cd-based telluride Ba 4 Cd 2 Ge 2 Te 9 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 [Cd 2 Ge 2 Te 9 ] 8- chains, with Ba 2+ filling in the interstitial space to balance the charge. The fluorescence spectrum indicates that the title compound generates purple-emission the range of 415–459 nm under the 300 nm excitation, with a peak lifetime of about 1.18 ns at 436 nm. In addition, first-principles calculations show that Ba 4 Cd 2 Ge 2 Te 9 has a birefringence of 0.298 @ 2090 nm, which is determined by the superposition of the polarization of the terminal Te atom and Ge 2 Te 6 unit. Thermoelectricity measurements show that the title compound possesses a large Seebeck coefficient (655 μV K −1 @300 K) and a low thermal conductivity (0.87 W m −1 K −1 @300 K).