Two quasi-one-dimensional compounds Ba9Nb2.54Te15 and Ba9Ta1.89Te15 were synthesized under high pressure and high temperature conditions and systematically characterized by structural, transport and magnetic measurements. Both the two compounds crystallize into a hexagonal structure with the space group P-6c2 (No. 188). The structure consists of trimeric face-sharing octahedral Nb/TaTe6 chains separated by a large distance (>10 Å), thus presenting a strong one-dimensional crystal structure. The transport properties suggest that both the two compounds are semiconductors with a band gap ∼ 0.15 eV for Ba9Nb2.54Te15 and ∼ 0.22 eV for Ba9Ta1.89Te15. Magnetic properties characterization indicates that Ba9Nb2.54Te15 displays no long-range-order above 2 K, but with an effective moment μeff ∼ 1.8 μB/f.u., while Ba9Ta1.89Te15 exhibits a diamagnetic behavior. Our results demonstrate that, in the sequence of Ba9V3Te15, Ba9Nb2.54Te15 and Ba9Ta1.89Te15, the occupation in the transition metal sites decreases, the semiconducting band gap increases, and the magnetism changes from ferromagnetism to diamagnetism.

中文翻译：

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两种准一维化合物Ba9Nb2.54Te15和Ba9Ta1.89Te15的高压合成、结构和物理性质


在高压高温条件下合成了两种准一维化合物Ba9Nb2.54Te15和Ba9Ta1.89Te15，并通过结构、输运和磁性测量系统地表征了它们。这两种化合物均结晶成具有空间群P-6c2（No.188）的六方结构。该结构由三聚体共面八面体 Nb/TaTe6 链组成，这些链之间的距离很大 (>10 Å)，从而呈现出强大的一维晶体结构。传输特性表明这两种化合物都是半导体，Ba9Nb2.54Te15 的带隙约为 0.15 eV，Ba9Ta1.89Te15 的带隙约为 0.22 eV。磁性能表征表明，Ba9Nb2.54Te15 在 2 K 以上不表现出长程有序，但有效矩 μeff ∼ 1.8 μB/fu，而 Ba9Ta1.89Te15 表现出抗磁性行为。我们的结果表明，在Ba9V3Te15、Ba9Nb2.54Te15和Ba9Ta1.89Te15序列中，过渡金属位点的占据减少，半导体带隙增加，磁性从铁磁性转变为抗磁性。