In recent years, the transition metal trichalcogenides (TX3) of Group IVB, VB and VIB have received much more attention because of the considerable diversity in their physical properties. The most striking feature of these compounds is that the structure here may be classified into three types depending on the number of different TX3 chains present in the unit cell. Thus ZrSe3, TaSe3 and NbSe3 are the representative compounds having one, two and three types of chain based on the different bond lengths for the (X2)2− pairs in the base of the TX3 trigonal prismatic framework. A similar model is also applicable in the case of NbS3, with the addition of a 2b-superstructure associated with the formation of niobium pairs. The chain structure also facilitates the process of intercalation which has been most effectively used in secondary batteries. These compounds exhibit the superconductivity phenomena and charge density wave, etc. and also find application in photoelectrochemical cells. An attempt has been made here to review the up-to-date chemistry of transition metal trichalcogenides related with their preparation, structure and properties such as physical and chemical, thermodynamic, electrical, magnetic and optical properties, intercalation and use in the photoelectrochemical cells. 93

Preparation, structure and properties of transition metal trichalcogenides

The strong in-plane anisotropy and quasi-1D electronic structures of transition-metal trichalcogenides (MX3; M = group IV or V transition metal; X = S, Se, or Te) have pronounced influence on moulding the properties of MX3 materials. In particular, the infinite trigonal MX6 prismatic chains running parallel to the b-axis are responsible for the manifestation of anisotropy in these materials. Several marvellous properties, such as inherent electronic, optical, electrical, magnetic, superconductivity, and charge density wave (CDW) transport properties, make transition-metal trichalcogenides (TMTCs) stand out from other 2D materials in the fields of nanoscience and materials science. In addition, with the assistance of pressure, temperature, and tensile strain, these materials and their exceptional properties can be tuned to a superior extent. The robust anisotropy and incommensurable properties make the MX3 family fit for accomplishing quite a lot of compelling applications in the areas of field effect transistors (FETs), solar and fuel cells, lithium-ion batteries, thermoelectricity, etc. In this review article, a precise audit of the distinctive crystal structures, static and dynamic properties, efficacious synthesis schemes, and enthralling applications of quasi-1D MX3 materials is made.

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Anisotropic quasi-one-dimensional layered transition-metal trichalcogenides: synthesis, properties and applications

We experimentally investigate the thermoelectric power (Seebeck effect) of quasi-two-dimensional single crystals of titanium and zirconium trichalcogenides (TiS3, ZrS3, ZrSe3, and ZrTe3) under applied high pressure up to 10 GPa. Both sulfides were characterized by n-type semiconducting conduction in the whole pressure range investigated and, generally, showed moderate pressure responses of their electronic properties. Metallic ZrTe3 conserved its p-type conduction under pressure, and its Seebeck coefficient curve displayed a distinct crossover near 2 GPa. Semiconducting ZrSe3 demonstrated more remarkable responses to applied pressure, which included a multiorder gradual drop in its electrical resistance value up to 9 GPa and an n–p inversion of the dominant conduction type around 6 GPa. Furthermore, we found that a thermoelectric power factor of ZrSe3 may be greatly improved under high applied pressure, achieving a value of an order of 3.5 mW/(K2 m) at 9.5 GPa. Thus, an appropriately strained p-type ZrSe3...

Thermoelectric Properties of Compressed Titanium and Zirconium Trichalcogenides

This article reviews a number of Van der Waals type layered semiconductors, which have been studied as photovoltaic base materials as well as window materials in heterostructures with other layered or nonlayered semiconductors. In particular, the compounds to be discussed are: GaSe, GaTe, InSe of the III–VI, and GeS, GeSe, SnS, SnSe, SnS2, SnSe2 of the IV–VI family. Others belong to the layered transitionmetal compound series: TiS3, ZrS2, ZrS3, ZrSe2, ZrSe3 and related compounds of Hf, as well as MoS2, MoSe2, MoTe2, WS2, WSe2. Because the photovoltaic performance depends on a number of electronic and optical parameters, these properties will also be thoroughly reviewed, along with other important aspects, such as crystalgrowth and doping possibilities. Most emphasis however will be given to the chapter reviewing the photovoltaic properties achieved so far and evaluating their potential for future applications.

Photovoltaic Properties of Solid State Junctions of Layered Semiconductors

Angle-resolved photoemission spectroscopy (ARPES) and optical measurements were performed on single crystal samples of ZrSe3, HfSe3, and ZrS3, which belong to the class of low-dimensional band insulators. By ARPES, we traced the dispersion of the (S 3p, Se 4p) p-derived valence states. In all cases, the topmost band exhibits energy splitting increasing from S to Se, which we attribute to the spin-orbit interaction, similar to recent observations in the related layered dichalcogenides. The combination of optical and photoemission results allows us to address the issue of the gap feature in the absorption spectra and to characterize the electronic and vibrational properties of ZrSe3, HfSe3, and ZrS3.

T. Ikari

Papers

Electrical properties of vapour grown ZrSe3 single crystals