Raman spectroscopy studies of the terahertz vibrational modes of a DUT-8 (Ni) metal-organic framework

Low-frequency lattice vibration modes have been discussed to play a crucial role in phase transformation process of switchable metal–organic frameworks (MOFs). Therefore, Raman spectroscopy was applied to study lattice dynamics of the pillared layer DUT-8(Ni) framework (DUT – Dresden University of Technology), existing in rigid and flexible form. The open pore phase and the close pore phase could be unanimously identified by breathing modes in the corresponding Raman character of low-frequency vibrations. The flexible version of DUT-8 could be distinguished by orientation dependent Raman spectroscopy experimen

Pressure–Temperature Phase Diagram of Multiferroic TbFe2.46Ga0.54(BO3)4

The pressure–temperature phase diagram of the multiferroic TbFe2.46Ga0.54(BO3)4 was studied for hydrostatic pressures up to 7 GPa and simultaneously with temperatures up to 400 K by the Raman spectroscopy technique. The structural phase transition from the R32 phase to the P3121 phase was determined by observing the condensation of soft modes and the appearance of new lines. An increase in pressure leads to an increase in the temperature of the structural phase transition. These phases are stable over the entire investigated temperature and pressure range. No other phases have been found

Gallium Composition-Dependent Structural Phase Transitions in HoFe3–xGax(BO3)4 Solid Solutions: Crystal Growth, Structure, and Raman Spectroscopy Study

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Single crystals of solid solutions of HoFe3–xGax(BO3)4 with x = 0, 0.5, 1, 1.5, and 3 were obtained using flux synthesis. The conditions of the synthesis are described in detail. The structural properties of each of the synthesized samples were studied using X-ray powder diffraction analysis at several temperature points (303, 403, and 503 K). The structural parameters of the obtained samples and the “pure” compounds HoFe3(BO3)4 and HoGa3(BO3)4 were compared. The Raman spectra of the obtained solid solutions HoFe3–xGax(BO3)4 were studied in a wide temperature range (T = 10–400 K). The vibrational spectra and eigenvectors of the HoFe3Ga(BO3)4 and HoGa3(BO3)4 in R32 phase and HoFe3Ga(BO3)4 in P3121 phase were calculated within density functional theory. The features of the Raman spectra of HoFe2Ga(BO3)4, HoFe2.5Ga0.5(BO3)4, HoFe3(BO3)4 crystals associated with the R32 → P3121 structural phase transition, which have a strong dependence on the degree of substitution x, were investigated. Peculiarities of the Raman spectra, which are associated with magnetic ordering in HoFe1.5Ga1.5(BO3)4, HoFe2Ga(BO3)4, and HoFe2.5Ga0.5(BO3)4 crystals, were detected

Single particle Raman spectroscopy analysis of the metal-organic framework DUT-8(Ni) switching transition under hydrostatic pressure

Experimental in situ observations of phase coexistence in switchable metal-organic frameworks are reported to provide a fundamental understanding of dynamic adsorbents that can change their pore structure in response to external stimuli. A prototypical flexible pillared layer framework DUT-8(Ni) (DUT = Dresden University of Technology) was studied under hydrostatic pressure by in situ Raman spectroscopy on single crystals. The closing transition of the open pore phase (op) containing DMF in the pores in silicon oil as a pressure transmitting fluid, as well as the closed pore phase (cp) to op transition under pressure in methanol, were studied. Phase coexistences during both transitions were observed

Soft modes condensation in Raman spectra of (Pb–La)(Zr–Sn–Ti)O3 ceramics

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Исследованы низкочастотные спектры комбинационного рассеяния керамики (Pb0:97La0:02)Zr0:864Sn0:04Ti0:096O3 в области фазового перехода из кубической в антисегнетоэлектрическую фазу при 200 С. В дополнение к ранее известной моде при 100 см-1, обнаружена группа низкочастотных мягких мод, восстанавливающихся ниже точки перехода. У этих мод в точке перехода наблюдаются резкие аномалии, что позволяет предположить существенное межмодовое взаимодействие через затухание

Crystal size versus paddle wheel deformability: selective gated adsorption transitions of the switchable metal–organic frameworks DUT-8(Co) and DUT-8(Ni)

Switchable pillared layer metal–organic frameworks M2(2,6-ndc)2(dabco) (DUT-8(M), M ¼ Ni, Co, 2,6-ndc ¼ 2,6- naphthalenedicarboxylate, dabco ¼ 1,4-diazabicyclo-[2.2.2]octane, DUT – Dresden University of Technology) were synthesised in two different crystallite size regimes to produce particles up to 300 mm and smaller particles around 0.1 mm, respectively. The textural properties and adsorption-induced switchability of the materials, obtained from both syntheses, were studied by physisorption of N2 at 77 K, CO2 at 195 K and nbutane at 273 K, revealing pronounced differences in adsorption behavior for Ni and Co analogues. While the smaller nano-sized particles (50–200 nm) are rigid and show no gating transitions confirming the importance of crystallite size, the large particles show pronounced switchability with characteristic differences for the two metals resulting in distinct recognition effects for various gases and vapours. Adsorption of various vapours demonstrates consistently a higher energetic barrier for the “gate opening” of DUT-8(Co) in contrast to DUT8(Ni), as the “gate opening” pressure for Co based material is shifted to a higher value for adsorption of dichloromethane at 298 K. Evaluation of crystallographic data, obtained from single crystal and powder X-ray diffraction analysis, showed distinct geometric differences in the paddle wheel units of the respective MOFs. These differences are further disclosed by solid-state UV-vis, FT-IR and Raman spectroscopy. Magnetic properties of DUT-8(Co) and DUT-8(Ni) were investigated, indicating a high-spin state for both materials at room temperature. Density functional theory (DFT) simulations confirmed distinct energetic differences for Ni and Co analogues with a higher energetic penalty for the structural “gate opening” transformation for DUT8(Co) compared to DUT-8(Ni) explaining the different flexibility behaviour of these isomorphous MOFs