Raman signatures of lattice dynamics across inversion symmetry breaking phase transition in quasi-1D compound, (TaSe4_4)3_3I

Structural phase transition can occur due to complex mechanisms other than simple dynamical instability, especially when the parent and daughter structure is of low dimension. This article reports such an inversion symmetry-breaking structural phase transition in a quasi-1D compound (TaSe$_4$)$_3$I at T$_S\sim$ 141~K studied by Raman spectroscopy. Our investigation of collective lattice dynamics reveals three additional Raman active modes in the low-temperature non-centrosymmetric structure. Two vibrational modes become Raman active due to the absence of an inversion center, while the third mode is a soft phonon mode resulting from the vibration of Ta atoms along the \{-Ta-Ta-\} chains. Furthermore, the most intense Raman mode display Fano-shaped asymmetry, inferred as the signature of strong electron-phonon coupling. The group theory and symmetry analysis of Raman spectra confirm the displacive-first-order nature of the structural transition. Therefore, our results establish (TaSe$_4)_3$I as a model system with broken inversion symmetry and strong electron-phonon coupling in the quasi-1D regime.Comment: Main text - 6 figures, 11 pages, supplementary - 10 figures, 13 page

Water-Stable Manganese(Iv) Complex Of A N2O4-Donor Non-Schiff-Base Ligand: Synthesis, Structure, And Multifrequency High-Field Electron Paramagnetic Resonance Studies

A novel water-stable (t1/2 ∼ 6.8 days) mononuclear manganese(IV) complex of a hexacoordinating non-Schiff-base ligand (H 4L) with N2O4-donor atoms has been synthesized and characterized crystallographically. High-frequency electron paramagnetic resonance experiments performed on a single crystal reveal a manganese(IV) ion with an S = 3/2 ground spin state that displays a large single-ion anisotropy, setting the record of mononuclear manganese(IV) complexes reported so far. In addition, spin-echo experiments reveal a spin-spin relaxation time T2 ∼ 500 ns. © 2014 American Chemical Society

Water-Stable Manganese(IV) Complex of a N₂O₄‑Donor Non-Schiff-Base Ligand: Synthesis, Structure, and Multifrequency High-Field Electron Paramagnetic Resonance Studies

A novel water-stable (<i>t</i>_1/2 ∼ 6.8 days) mononuclear manganese­(IV) complex of a hexacoordinating non-Schiff-base ligand (H₄L) with N₂O₄-donor atoms has been synthesized and characterized crystallographically. High-frequency electron paramagnetic resonance experiments performed on a single crystal reveal a manganese­(IV) ion with an <i>S</i> = ³/₂ ground spin state that displays a large single-ion anisotropy, setting the record of mononuclear manganese­(IV) complexes reported so far. In addition, spin–echo experiments reveal a spin–spin relaxation time <i>T</i>₂ ∼ 500 ns

Water-Stable Manganese(IV) Complex of a N₂O₄‑Donor Non-Schiff-Base Ligand: Synthesis, Structure, and Multifrequency High-Field Electron Paramagnetic Resonance Studies

A novel water-stable (<i>t</i>_1/2 ∼ 6.8 days) mononuclear manganese­(IV) complex of a hexacoordinating non-Schiff-base ligand (H₄L) with N₂O₄-donor atoms has been synthesized and characterized crystallographically. High-frequency electron paramagnetic resonance experiments performed on a single crystal reveal a manganese­(IV) ion with an <i>S</i> = ³/₂ ground spin state that displays a large single-ion anisotropy, setting the record of mononuclear manganese­(IV) complexes reported so far. In addition, spin–echo experiments reveal a spin–spin relaxation time <i>T</i>₂ ∼ 500 ns

Enhanced Thermoelectric Properties of Selenium-Deficient Layered TiSe_2–<i>x</i>: A Charge-Density-Wave Material

In the present work, we report on the investigation of low-temperature (300–5 K) thermoelectric properties of hot-pressed TiSe₂, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe₂ increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe₂ leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (<i>ZT</i>) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10^–7 obtained for cold-pressed samples annealed at 850 °C. The enhancement of <i>ZT</i> in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α²σ)