title: Structure and properties of type-II clathrate Cs8Na16-xTlxGe136.
abstract: Tl-doped type-II clathrate Cs8Na16-xTlxGe136 was synthesized from its elements. The structure was characterised by single crystal and powder diffraction. Cs8Na16-xTlxGe136 crystallized in the space group Fd3[combining macron]m. The melting point decreased with increasing Tl content at 925.0 °C, 922.8 °C and 915.7 °C for Cs8Na14.76(3)Tl1.24(2)Ge136, Cs8Na9.94(2)Tl6.06(2)Ge136 and Cs8Na8.36(2)Tl7.64(2)Ge136 in Ar atmosphere, respectively. Cs8Na9.94(2)Tl6.06(2)Ge136 exhibited diamagnetism with χ = -3.11 × 10(-3) emu mol(-1) at 1.8 K. The heat capacity of Cs8Na9.94(2)Tl6.06(2)Ge136 presented an Einstein peak at 10 K. The fitted parameters for Cs8Na9.94(2)Tl6.06(2)Ge136 were λ = 0.115(4) J mol(-1) K(-2), β = 0.0289(2) J mol(-1) K(-4), NE = 7.94(4), θE = 56.9(1) K, ND = 152.06(4) and θD = 217(1) K using the equation Cp = Ce + CD + CE from 1.8 K to 10 K. The thermoelectric measurement showed metallic resistivity and a negative Seebeck coefficient, indicating electron-type charge carriers. The electronic structure calculation for Cs8Na10Tl6Ge136 confirmed the nature of the metallic transport behavior with conducting electrons, mainly from the Ge p orbitals.
authors.affiliation: CAS Key Laboratory of Materials for Energy Conversion and State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, P. R. China. huangfq@mail.sic.ac.cn.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Xuguang
authors.initials: X
authors.lastname: Xu
authors.forename: Gang
authors.initials: G
authors.lastname: Mu
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Xie
authors.forename: Fuqiang
authors.initials: F
authors.lastname: Huang