Monoclinic structures of niobium trisulfide

Abstract

Two new polymorphs of niobium trisulfide are established by single crystal x-ray diffraction. NbS3-iv crystallizes in the monoclinic space group P21/c with lattice parameters a = 6.7515(5) Å, b = 4.9736(4) Å, c = 18.1315(13) Å, and β = 90.116(2)°. Its structure is based on chains of [NbS6] trigonal prisms containing Nb–Nb pairs with a bond length of 3.0448(8) Å; this pairing causes the chains to corrugate slightly along their axis, a feature also present in triclinic NbS3-i that leads to semiconductor properties. The stacking arrangement of chains is different in these polymorphs, however, with NbS3-i having an ABCDE repeating sequence of chain bilayers and NbS3-iv having an AB repeating sequence. HRTEM studies show the presence of topotactically-oriented intergrown zones and numerous dislocations, which result in mosaic structuring. A second new polymorph, NbS3-v, crystallizes in the monoclinic space group P21/m with lattice parameters a = 4.950(5) Å, b = 3.358(4) Å, c = 9.079(10) Å, β = 97.35(2)°. In contrast to NbS3-iv, NbS3-v maintains fixed a Nb–Nb bond distance of 3.358(4) Å along the chains, and it has an ABCDE repeating sequence of chain bilayers similar to NbS3-i. High resolution scanning transmission electron microscopy (HR-STEM) imaging of an exfoliated NbS3-v nanoribbon shows the continuous [NbS6] chains oriented along the b-axis. These results provide the first firmly established structural data for monoclinic NbS3. In addition, SEM images show the formation of NbS3 rings and cylinders, and a combination of powder x-ray diffraction and Raman spectroscopy provides a way to distinguish between NbS3 polymorphs.

Pressure-induced reentrant transition in NbS3 phases: Combined Raman scattering and x-ray diffraction study

“…The x-ray powder diffraction pattern for the NbS3-II sample under ambient pressure at room temperature is shown in Fig. 1a, from which the good crystalline data can be fitted to a monoclinic structure with lattice parameters of a = 9.84 Å, b = 3.39 Å, and c = 19.01 Å, with β  97.4˚, close to the reported values of a = 9.65 Å, b = 3.345 Å, and c = 18.75 Å, with β  98.7˚ [2,17,33]. The Raman spectrum of NbS3-II at room temperature is shown in Fig.…”

Basic and charge density wave modulated structures of NbS3 -II

“…As for a few other MX 3 compounds, e.g. NbSe 3 and the monoclinic polymorph of TaS 3 (m-TaS 3 ) 11,12 , pairs of IC satellites in the electron DPs of NbS 3 -II 6 correspond to two CDWs with satellites at position (0.5, 0.298, 0) and (0.5, 0.352, 0) 2,13,14 . The non-zero x-parameters (0.5) of these positions are in fact a result of the extinction rules, imposed by the modulation space group, while the actual modulation of both CDWs is directed along the columns with q 1 = (0, 0.298,0) and q 2 = (0, 0.352, 0).…”

“…Introduction.-A large number of quasi one-dimensional (1D) transition-metal trichalcogenides (MX 3 ), which all possess related structures 1,2 , are now known. They are composed of bi-caped trigonal prismatic (TP) columns, formed of chalcogen atoms and centered by metallic chains.…”

Natural abundance solid-state 33S NMR study of NbS3: applications for battery conversion electrodes

“…Chain polytypism can result from variations in the stacking arrangements of chains and/or sheets. 27,28 Powder XRD patterns of our NbS3 samples ( Figure SI1) show absent (h0l) reflections, which suggest disorder in the stacking sequences of NbS3 sheets along c. 28,29 Importantly for the NMR experiments, the local S environments are unaffected by stacking faults as the registry between NbS3 sheets is independent of the stacking configuration (further details provided in Figure SI2 and the SI). As seen in related early-TM oxides and sulfides such as VO2 and VS4, [30][31][32] the NbS3 chains undergo a linear Peierls distortion wherein adjacent Nb sites pair to give alternating short (3.0 Å) and long (3.7 Å) Nb-Nb distances.…”