A new quasi-one-dimensional transition metal chalcogenide semiconductor (Nb4Se15I2)I2
Abstract
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 new quasi-one-dimensional material (Nb4Se15I2)I2 were grown by chemical vapor transport, and the structure was solved by single crystal X-ray diffraction (XRD). The new structure has one-dimensional (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 intercalate 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 was 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 micro-patterned devices demonstrate that (Nb4Se15I2)I2 has an activation energy of around 0.1 eV, and no anomaly or transition was seen upon cooling. (Nb4Se15I2)I2 does not undergo structural phase transformation from room temperature down to 8.2 K, based on cryogenic temperature single crystal XRD. This compound represents a well-characterized and valence-precise member of a diverse family of anisotropic transition metal chalcogenides.
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