Rich Polymorphism of Layered NbS₃

Abstract

Layered group V transition-metal trichalcogenides are paradigmatic low-dimensional materials providing an ever increasing series of unusual properties. They are all based on the same basic building units, one-dimensional MX 3 (M = Nb, Ta; X = S, Se) trigonal-prismatic chains that condense into layers, but their electronic structures exhibit significant differences leading to a broad spectrum of transport properties, ranging from metals with one, two, or three charge density wave instabilities to semimetals with potential topological properties or semiconductors. The different physical and chemical properties are shown to be related with subtle structural differences within the layers that result in half-, third-, or quarter-filled quasi-one-dimensional Nb d z 2 -type bands, providing a clear-cut illustration of the intimate link between structural and electronic features within a family of solids. An interesting yet not sufficiently explored feature of these solids is the polymorphism. Based on both experimental and new theoretical results, we examine this aspect for NbS 3 and show that at least seven different polymorphs with a stability compatible with the presently known phases of this compound are possible. We discuss a simple rationale for the physical properties of the presently known polymorphs as well as predictions for those that have still not been characterized or prepared. It is argued that some of the presently unknown polymorphs may have been prepared in an uncontrolled way as mixtures of different phases which could not be structurally characterized. The rich landscape of structures and properties found for this van der Waals material is suggested to represent an ideal platform for the preparation of flakes with finetuned properties for applications in new electronic and optoelectronic devices.

Similar and Dissimilar Properties of Polymorphic Phases of NdIr3

“…Carbon, sulfur, phosphorus, , iron, , and so forth are well known to have different allotropes, and the physical properties of one crystal structure could be quite contrasting to those of another. Apart from the case of such above-mentioned elements, one may find quite a few examples of binary or ternary compounds that can exhibit different crystal structures under ambient conditions. − For example, LaIr 2 Si 2 and PrIr 2 Si 2 have been reported to form two different tetragonal crystal structures (viz., CaBe 2 Ge 2 -type and ThCr 2 Si 2 -type), and the properties of these two phases have much contrast. , For LaIr 2 Si 2 , the phase formed in the CaBe 2 Ge 2 -type crystal structure undergoes a superconducting transition below 1.6 K, whereas the other polymorphic phase that forms in the ThCr 2 Si 2 -type crystal structure lacks that pristine property . Even in the case of PrIr 2 Si 2 , the magnetic properties of two polymorphic phases have also been reported to be quite different .…”

Formation of a Polar Structure in the Metallic Niobium Sulfide Nb4S3

“…The crystal structure of NbS 3 can be rationalized as Nb(S 2 )S, containing alternating short and long Nb−Nb distances in the structure, and possesses an intricate series of structural and electronic states arising from charge-density waves. 7 NbS 3 has both semiconducting and metallic polymorphs, whereas all other niobium sulfides are metallic, or low T c superconductors. 7,8,14,15 Niobium disulfide (NbS 2 ) is a 2D metallic transition-metal dichalcogenide with interesting anisotropic magnetic, optical, and superconducting (T c = 6.3 K) properties.…”

“…7 NbS 3 has both semiconducting and metallic polymorphs, whereas all other niobium sulfides are metallic, or low T c superconductors. 7,8,14,15 Niobium disulfide (NbS 2 ) is a 2D metallic transition-metal dichalcogenide with interesting anisotropic magnetic, optical, and superconducting (T c = 6.3 K) properties. 2,17 It appears with three stacking polytypes1T (trigonal), 2H (hexagonal), and 3R (rhombohedral)and has been investigated as a cathode material in lithium batteries.…”

“…Binary metal sulfides have been the subject of considerable research efforts because of their diverse electronic, electrical, and optical properties. − It can be assumed that the vast majority of binary metal sulfides have already been discovered. Some missing compounds may still be expected, but new phases are hard to predict in metal-rich systems, especially those with nonrational compositions.…”

“…The presence of excess electrons in these systems allows for interesting physical effects related to electronic correlations. The crystal structure of NbS 3 can be rationalized as Nb­(S 2 )­S, containing alternating short and long Nb–Nb distances in the structure, and possesses an intricate series of structural and electronic states arising from charge-density waves . NbS 3 has both semiconducting and metallic polymorphs, whereas all other niobium sulfides are metallic, or low T c superconductors. ,,, …”