Li 2 TeS 3 and Li 2 TeSe 3 : Preparation, Crystal Structure and Impedance Spectroscopic Characterization

Li 2 TeS 3 and Li 2 TeSe 3 were synthesized by the reaction of stoichiometric amounts of Li, Te and Q (Q = S, Se) in the ratio 2 : 1 : 3. Both products are extremely air and moisture sensitive. The crystal structures were determined by single crystal X‐ray diffraction at room temperature. Red Li 2 TeS 3 and metallic black Li 2 TeSe 3 crystallize isotypically in the monoclinic space group P 2 1 / c (no. 14) with four formula units per unit cell and the lattice parameters: Li 2 TeS 3 : a = 5.437(1) Å, b = 11.564(1) Å, c = 7.907(1) Å, β = 91.57(1)°, V = 496.96(1) Å 3 ; Li 2 TeSe 3 : a = 5.658(1) Å, b = 12.032(1) Å, c = 8.278(1) Å, β = 92.690(1)°, V = 562.93(1) Å 3 (data at 20 °C). The atomic arrangements persist of isolated trigonal pyramidal [TeQ 3 ] 2− anions which are arranged in layers. Li is coordinated by six Q atoms from four (Li1) or five (Li2) different thiotellurate or selenidotellurate units, respectively. Impedance spectroscopic measurements in the temperature range 90 – 200 °C show that Li 2 TeS 3 is a semiconductor with an activation energy of 0.71 eV. Li 2 TeSe 3 is a mixed conductor with an activation energy of 0.68 eV.