Synthesis, crystal structure and high-temperature transport properties of the new cluster compound Rb2Mo15Se19

We report on the synthesis, crystal structure and high-temperature transport properties of Rb2Mo15Se19, a new member of the large family of M2Mo15Se19 (M=In, Tl, K, Ba) cluster compounds. Polycrystalline samples and single crystals of the ternary selenide Rb2Mo15Se19 were obtained by solid-state reactions. The trigonal crystal structure, successfully refined in space group R3¯c (No. 167) with unit-cell parameters a=9.7618(1)Å, c=58.254(1)Å and Z=6, was determined by single-crystal X-ray diffraction. The crystal structure contains Mo6Se8iSe6a and Mo9Se11iSe6a cluster units in equal proportion and separated from each other by large voids, which are filled up by Rb atoms. Measurements of the electrical resistivity, thermopower and thermal conductivity revealed that Rb2Mo15Se19 behaves as a p-type metal with relatively low electrical resistivity and thermopower. Despite its complex crystal structure, the lattice thermal conductivity that amounts to 1.3Wm−1K−1 at 300K is significantly higher than in Ag-filled analogues, which provides possible guidelines to enhance its thermoelectric properties. The crystal structure of the new cluster compound Rb2Mo15Se19 contains octahedral Mo6 and bioctahedral Mo9 clusters in equal proportion forming Mo6Se8iSe6a and Mo9Se11iSe6a cluster units separated from each other by large voids filled by Rb atoms. Measurements of the electrical resistivity, thermopower and thermal conductivity revealed that Rb2Mo15Se19 behaves as a p-type metal with relatively low electrical resistivity and thermopower. [Display omitted] •Successful synthesis of single-crystalline and polycrystalline Rb2Mo15Se19.•Crystal structure contains octahedral and bioctahedral clusters in equal proportion.•Rb2Mo15Se19 is a p-type metal with low electrical resistivity and thermopower.•The lattice thermal conductivity is higher compared to Ag-filled analogues.