Quasi-One-Dimensional Transition-Metal Chalcogenide Semiconductor (Nb4Se15I2)I2

The discovery of new low-dimensional transition-metal chalcogenides is contributing to the already prosperous family of these materials. In this study, needle shaped single crystals of a quasi-one-dimensional (1D) material, (Nb4Se15I2)I2, were grown by chemical vapor transport, and the structure was solved by single-crystal X-ray diffraction (XRD). The structure has 1D (Nb4Se15I2)n chains along the [101] direction, with two I- ions per formula unit directly bonded to Nb5+. The other two I- ions are loosely coordinated and intercalated between the chains. Individual chains are chiral and stack along the b axis in opposing directions, giving space group P21/c. The phase purity and crystal structure were verified by powder XRD. Density functional theory calculations show (Nb4Se15I2)I2 to be a semiconductor with a direct band gap of around 0.6 eV. Resistivity measurements of bulk crystals and micropatterned devices demonstrate that (Nb4Se15I2)I2 has an activation energy of around 0.1 eV, and no anomaly or transition was seen upon cooling. Low-temperature XRD shows that (Nb4Se15I2)I2 does not undergo a structural phase transformation from room temperature to 8.2 K, unlike related compounds (NbSe4)nI (n = 2, 3, or 3.33), which all exhibit charge-density waves. This compound represents a well-characterized and valence precise member of a diverse family of anisotropic transition-metal chalcogenides.

Automated summary

The structure of quasi-one-dimensional material (Nb4Se15I2)I2, consisting of needle shaped single crystals, was determined by single-crystal X-ray diffraction. The structure features 1D (Nb4Se15I2)n chains along the [101] direction, with two directly bonded I- ions per formula unit to Nb5+, and two loosely coordinated I- ions intercalated between the chains. The compound is chiral, with stacks of chains in opposing directions along the b axis, belonging to space group P21/c. It is a well-characterized semiconductor with a direct band gap of around 0.6 eV, confirmed by density functional theory calculations. Resistivity measurements show an activation energy of around 0.1 eV, and no structural phase transformation was observed from room temperature to 8.2 K, unlike related compounds (NbSe4)nI (n = 2, 3, or 3.33).