NbS3: A unique quasi-one-dimensional conductor with three charge density wave transitions

Abstract

Through transport, compositional and structural studies, we review the features of the chargedensity wave (CDW) conductor of NbS3 (phase II). We highlight three central results: 1) In addition to the previously reported CDW transitions at TP 1 = 360 K and TP 2 = 150 K, another CDW transition occurs at a much higher temperature TP 0 = 620-650 K; evidence for the non-linear conductivity of this CDW is presented. 2) We show that CDW associated with the TP 2 -transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. 3) We show exceptional coherence of the TP 1-CDW at room-temperature. Additionally, we report on the effects of uniaxial strain on the CDW transition temperatures and transport.

Monoclinic structures of niobium trisulfide

“…26,31,32 In the almost forty years since NbS 3 -ii was identified, however, its atomic structure has remained unsolved. During this time, continued interest in this polymorph has been motivated by its three CDWs: a low temperature transition at 150 K, a second transition at 330-370 K, and a high temperature transition at 620-650 K. 21,26 The transition at 330-370 K, just above room temperature, is an unusual one for CDW transport, and according to Zybtsev and co-workers, this CDW exhibits high transport velocities and sliding coherence. 21 A high-pressure modification of NbS 3 prepared at 700 • C with 2 GPa pressure was reported by Kikkawa and co-workers in 1982.…”

“…During this time, continued interest in this polymorph has been motivated by its three CDWs: a low temperature transition at 150 K, a second transition at 330-370 K, and a high temperature transition at 620-650 K. 21,26 The transition at 330-370 K, just above room temperature, is an unusual one for CDW transport, and according to Zybtsev and co-workers, this CDW exhibits high transport velocities and sliding coherence. 21 A high-pressure modification of NbS 3 prepared at 700 • C with 2 GPa pressure was reported by Kikkawa and co-workers in 1982. 33 The monoclinic unit cell deduced from powder x-ray diffraction data is similar to that of monoclinic NbSe 3 (Table I), but atomic positions for NbS 3 -HP could not be determined.…”

“…However, NbS 3 -iii can be distinguished by a characteristic CDW transition at 155 K. 20 Subsequent electrical measurements by Zybtsev and co-workers on "low-ohmic" and "high-ohmic" NbS 3 samples showed that low-ohmic NbS 3 exhibits CDW transitions at both 150 and 360 K, whereas high-ohmic NbS 3 exhibits a single CDW transition at 150 K. 3 On this basis, it has been postulated that low-ohmic and high-ohmic NbS 3 correspond to NbS 3 -ii and NbS 3 -iii, respectively; an alternate interpretation is that low-and high-ohmic NbS 3 as well as NbS 3 -iii are sub-phases of NbS 3 -ii. 21 This letter reports the growth and characterization of two new monoclinic polymorphs of NbS 3 , designated NbS 3 -iv and NbS 3 -v following the nomenclature currently in place. Interestingly, we isolated NbS 3 -iv under synthetic conditions previously reported to produce NbS 3 -i and NbS 3 -v under synthetic conditions previously reported to produce NbS 3 -ii.…”

“…[16][17][18][19] Offsetting this complexity and piquing our interest are intriguing reports about the electrical and charge density wave (CDW) properties of certain NbS 3 samples, including multiple CDW transitions and room temperature charge transport. 3,20,21 However, further progress has been impeded by the absence of well-established structural information, spectroscopic characterization, or even reproducible synthetic details. Therefore, in this contribution, we aim to clarify the polymorphism of NbS 3 as part of the foundation required to understand its electronic properties.…”

Multi-terminal electronic transport in boron nitride encapsulated TiS3 nanosheets

“…Similar to other 2D semiconducting systems like MoS 2 [16] and WSe 2 [17] on SiO 2 , the devices showed disorder-induced electron localization even at high temperatures and high carrier densities. Moreover, degradation of the TiS 3 sheets during device fabrication procedure should not be excluded as a result of polymer-impurity contamination, as well as to exposure to air and moisture even at moderate temperatures, similar to NbS 3 and MoS 2 [18,19].…”