High-Pressure Synthesis and Structure of Quasi-One-Dimensional Ba3MSe5 (M = Ti, Zr, and Hf)

The ternary selenides Ba3MSe5 (M = Ti, Zr, and Hf) were successfully synthesized through a solid-state reaction under high-pressure and high-temperature conditions. These compounds crystallize in a hexagonal structure, consisting mainly of one-dimensional (1D) face-sharing MSe6 octahedral chains and Se chains. The intriguing superlattice along 1D chains was identified by theoretically calculating the Fermi surface and phonon spectrum of the Ba3MSe5 primitive cell (where M = Ti, Zr, and Hf). These superlattices exhibit average tetramerization, trimerization, and the primitive structures, respectively, as the M metal ions change from the 3d to 5d period. For the Ti- and Zr-containing compounds, the c-axis lengths are four times and three times that of the primitive structure, respectively. The space groups of P31c, P6c2, and P63/mcm were compatible with the Ti, Zr, and Hf selenides, respectively, resulting in the lattice parameters of a = 9.5304(8) & Aring; and c = 25.3505(3) & Aring; for Ba12Ti4Se20, a = 9.5677(2) & Aring; and c = 19.1731(6) & Aring; for Ba9Zr3Se15, and a = 9.5756(1) & Aring; and c = 6.3802(7) & Aring; for Ba3HfSe5. Comprehensive structural characterizations found that the vacancies on M sites increase from similar to 20% to similar to 40% and that the electronic hopping between interchains decreases in the Ba3MSe5 (M = Ti, Zr, and Hf) system as the M ions evolve from Ti to Hf, which dominates the electronic transport behaviors and results in a gradually increased band gap.