Structure and Thermoelectric Properties of SrBiTe 3 ; 12-Fold Superstructure Caused by Distortion of the Two-Dimensional Te-Nets

The ternary compound, SrBiTe 3 , was prepared by the molten flux method. It crystallizes in the orthorhombic space group Pmmn with a=4.665(2)Å, b=4.517(2)Å, c=16.129Å, and Z=2. The compound is composed of a NaCl-type [Bi 2 Te 4 ] 2- layer and a flat square (Te 2 ) 2- net with equal Te-Te distances of 3.24Å. The Sr 2+ ions are stabilized between the layers in monocapped square antiprismatic sites. X-ray and electron diffraction studies reveal a 12-fold superstructure due to subtle distortions within the Te net of the compound. The superstructure was refined in the monoclinic space group C2 with a=27.923(5)Å, b=32.228(6)Å, c=4.5069(9)Å, β=90.000(3)°. The compound is a semiconductor with a band gap value of 0.14 eV. It melts incongruently at 613 °C.