Fig 1 - uploaded by Xiaozhi Yang
Content may be subject to copyright.
Ambient a IR and b Raman spectra of hydrous wadsleyite. The IR spectrum was normalized to 1 mm thickness (the Raman spectra were measured with a LabRAM spectrometer at a 15 mW laser power)
Source publication
In situ Raman spectra of hydrous wadsleyite (β-Mg2SiO4) with ~1.5 wt% H2O, synthesized at 18GPa and 1,400°C, have been measured in an externally heated diamond anvil cell up to 15.5GPa and 673K.
With increasing pressure (at room temperature), the three most intense bands at ~549, 720 and 917cm−1 shift continuously to higher frequencies, while with...
Contexts in source publication
Context 1
... concentration of the synthesized wadsleyite was determined using a Bruker IFS 120 FTIR spectrometer coupled with a Bruker IR microscope (a tungsten light source and a Si-coated CaF 2 beam splitter). Unpolarized analysis was conducted on a double-polished single-crystal section (*30 lm thick). The spectrum (Fig. 1a) was integrated from about 3,800-2,800 cm -1 , and the mineral- specific calibration coefficient of 73,000 L/(mol cm 2 ) from Deon et al. (2010) was used to estimate the water content with an orientation factor of 1/3 (Paterson 1982). The yielded water content is *1.5 wt% H 2 O, and the uncer- tainty is about 30-50% caused mainly by the ...
Context 2
... IR spectrum of the hydrous wadsleyite shows signifi- cant H-related absorption bands at *3,000, 3,307, 3,326, 3,367, 3,583, 3,613 and 3,652 cm -1 (Fig. 1a). These are typical bands induced by OH-stretching vibrations, which have been well documented in previous reports for hydrous b-Mg 2 SiO 4 (Bolfan- Casanova et al. 2000;Jacobsen et al. 2005;Kohlstedt et al. 1996). In contrast, however, the Raman spectrum demonstrates no OH activities in such frequency region at all. One possibility is ...
Context 3
... modes of the hydrous wadsleyite in the range of 200-1,100 cm -1 at ambient conditions and prior to loading into DAC are shown in Fig. 1b, and Table 1 compares our data with previous results of the ambient Raman frequen- cies of b-Mg 2 SiO 4 with various water contents including partial mode assignments (Chopelas 1991; Kleppe et al. 2001;Liu et al. 1994Liu et al. , 1998McMillan et al. 1991;Mernagh and Liu 1996). In general, the frequencies of the Raman bands of these ...
Context 4
... on its silicate framework lattice dynamics as partially reflected by the activities of its Raman modes ( Kleppe et al. 2001). The Raman modes of the hydrous wadsleyite measured in DAC at room condi- tions are a little different from those measured out of DAC, and only three most intense bands at *549, 720 and 917 cm -1 can be readily resolved (Fig. 1b). This is caused by the diamond fluorescence, which affected the mea- surement of the sample at the very low laser ...
Citations
... inside the Si 3 O 9 chains of serandite in Fig. 6, together with those of common silicate minerals in the upper mantle and the transition zone: such as forsterite (Mg 2 SiO 4 olivine) (Gillet et al. 1991(Gillet et al. , 1997Yang et al. 2015), pyrope (Mg 3 Al 2 Si 3 O 12 garnet) (Gillet et al. 1992;Kolesov and Geiger 2000), enstatite (MgSiO 3 orthopyroxene) (Zucker and Shim 2009), wadsleyite (β-Mg 2 SiO 4 ) Yang et al. 2012), as well as akimotoite (MgSiO 3 ilmenite) (Reynard and Rubie 1996;Okada et al. 2008). The Si 4+ cations are 6-coordinated in akimotoite, while in 4-coordination with O in the other silicate phases. ...
... The discrete peaks at 1389, 1623, as well as 1964 cm −1 (with a shoulder at 1988 cm −1 ) can be clearly identified at all polarization angles except 90°. The relatively strong mode at 1389 cm −1 is ascribed to the OH-bending Gillet et al. 1991Gillet et al. , 1997Yang et al. 2015) and pyrope (open diamonds, Gillet et al. 1992;Kolesov and Geiger 2000), Si 2 O 7 groups in wadsleyite (gray squares, Yang et al. 2012 mode, which was also observed at 1386 cm −1 with E//c by Hammer et al. (1998). The Raman-active OH-bending mode has also been observed at 1378 cm −1 for serandite (see above), at a frequency ~ 10 cm −1 lower than the IR-active mode. ...
We collected in situ high-temperature powder X-ray diffraction (XRD) patterns, as well as Raman and Fourier transform infrared (FTIR) spectra on a natural serandite sample. The volumetric thermal expansion coefficient αV (K⁻¹) is determined as a linear function of T (K): 37.6(5) × 10⁻⁹ × T + 11.1(3) × 10⁻⁶, with an averaged value of 31.7(10) × 10⁻⁶ K⁻¹, while the anisotropy of axial thermal expansivities shows the order of αa > αb > αc. The isobaric Grüneisen parameters γiP are constrained as: 0.2–1.6 for most of the lattice vibrations below 500 cm⁻¹; while 0–0.6 for the O–Si–O bending and Si–O stretching modes inside the Si3O9 chains above 500 cm⁻¹. As compared with common silicate phases in the upper mantle and the transition zone, the γiP parameters for the internal vibrations are significantly smaller in silicate chains (serandite, enstatite) than those in Si2O7 groups (wadsleyite) and isolated SiO4 units (forsterite, pyrope), since the rotation of the bridging O atoms (in the direction perpendicular to Si–O–Si) could relax the SiO4 tetrahedra at elevated temperature. The OH-bending vibration of serandite is observed in both Raman-active (1378 cm⁻¹) and IR-active (1389 cm⁻¹) modes, with a temperature-dependence of − 0.07 and − 0.09 cm⁻¹/K, respectively. The red-shift of these OH-bending modes with increasing temperature indicates that the hydrogen bond gets weaker as the O3…O4 distance becomes larger during thermal expansion. Additionally, our polarized FTIR spectra confirm that the stretching mode of the very strong hydrogen bond, a broad absorption region (1400–3300 cm⁻¹), is polarized in the direction of E//b, as reported by Hammer et al. (Am Mineral 83:569–576, 1998).
... Numerous experiments at high temperature and pressure showed that olivine can contain considerably more water even up to 8900 ppm (wt) Mosenfelder et al. 2006;Smyth et al. 2006;Férot and Bolfan-Casanova 2012). According to the previous high-pressure Raman spec-troscopic studies on hydrous and anhydrous wadsleyite (Chopelas 1991;Liu et al. 1994Liu et al. , 1998Kleppe et al. 2001;Yang et al. 2012), the g iT parameters are similar between hydrous wadsleyite samples with different water contents, while they are different from those of anhydrous wadsleyite. As a result, water rather than its content is significant to influence the anharmonicity of wadsleyite. ...
To quantify the effects of hydration on anharmonicity of olivine thermodynamics, we have measured in situ Raman spectra of an extremely hydrous forsterite with 4500 ppm (wt) H2O at temperatures up to 1273 K. All the Raman modes in hydrous forsterite shift linearly to lower wavenumbers with increasing temperature. The calculated isobaric mode Grünesien parameters related to SiO4 internal stretching and bending vibrations are much lower than lattice vibrations. Additionally, compared with anhydrous forsterite, except for the modes at 919, 858, and 227 cm-1, water greatly reduces the isobaric mode Grüneisen parameters of the Raman modes in forsterite. Water also has a large effect on the anharmonic parameters related to lattice vibrations, whereas it has little effect on the anharmonic parameters related to SiO4 internal stretching and bending vibrations. Those results have the implications to the variations of local structure with temperature and estimation of water effects on the thermodynamics of forsterite.
... We believe that this is the first report of Raman spectra of Fe 3 Se 4 , and therefore, due to the absence of any previous report on Raman spectra of Fe 3 Se 4 in the literature, we compared our results with those for β-Mg 2 SiO 4 , which crystallizes in a similar I2/m space group symmetry. 15,16 The peaks at ∼228 and 411 cm −1 in Fe 3 Se 4 spectra can be assigned to lattice vibration (Figure 3). The shift in Raman peak position as a function of Mn doping concentration is shown in Figure 4. ...
Fe3Se4 possesses a large coercivity at room temperature. At lower temperature, a coercivity value up to 40 kOe has been achieved. However, due to a relatively lower saturation magnetization value, the energy product of this material is not suitable for its use as rare-earth-free hard magnetic material. Although the anisotropy and magnetic structure of Fe3Se4 have been topics of research, there is no attempt to increase the energy product. Here, we report the synthesis of Fe3–xMnxSe4 (x = 0.01–0.2) nanorods. As required for practical applications, after doping, the Curie temperature remains unchanged; however, at optimum (x = 0.03) doping of manganese ions, the magnetization of the host matrix increases significantly from 4.84 to 7.54 emu/g. The corresponding energy product value was found to be increased by more than 130%. At low temperature (10 K) the energy product shows almost a 2 order of magnitude increase (0.12 MG Oe), which makes it valuable for many low temperature applications. This improvement is a vital step for its use in some of the household applications where a large volume and relatively lower energy product are needed.
The transition zone is dominated by polymorphs of olivine, wadsleyite, and ringwoodite, which are to date considered the main water carriers in the Earth’s mantle. Despite considerable studies on water solubility and its impact on physical properties of the two minerals, knowledge of their hydrogen defects and framework behavior at high temperature and high pressure is still lacking. Here, we systematically assess this issue, by in situ high-temperature (20–800 °C) infrared spectroscopic studies, in situ high-temperature (20–800 °C) and high temperature-pressure (14.27 and 18.84 GPa, 20–400 °C) Raman spectroscopic studies on the iron-bearing wadsleyite and ringwoodite. The results show that dehydrogenation in wadsleyite happens at a higher temperature than in ringwoodite. The infrared absorption patterns of hydrogen defects in wadsleyite and ringwoodite are temperature sensitive, resulting from hydrogen defects transfer and site-specific stabilities. As for the framework, it is more sensitive to temperature and pressure for ringwoodite than wadsleyite. These results provide new knowledge about hydrogen defects and framework of wadsleyite and ringwoodite at high temperature and high pressure, which is indispensable for understanding water solubility and its impacts on physical properties of these two minerals.
One of the critical challenges in energy conversion using fuel cells is the development of non-Pt based electrocatalysts with high activity and stability. Herein, CeO2 nanoclusters of 1.5 nm supported on 1-pyrenecarboxylic acid (PC) functionalized multi-walled carbon nanotubes (PC-MWNTs) were synthesized via sequential polyelectrolyte functionalization and microwave-assisted self-assembly, and subsequently used as a support of gold (Au) NPs for glycerol oxidation reaction. The hybrid Au/CeO2/PC-MWNT electrocatalyst shows excellent activity and durability, achieving a peak current density 28 times that of the commercial Pt/C catalyst; at a practical fuel cell operation potential of -0.3 V vs. SCE, it exhibits a current density 1.6 times that of Pt/C. In addition, after polarization at -0.3 V vs. SCE for 1800s, the current density is 2.5 times that of Pt/C. This is probably the first report of a higher catalytic performance of Au-based catalysts than that of the commercial Pt/C catalysts at practical fuel cell operation potentials. The work not only provides an economical and facile strategy to synthesize oxide-based nanoclusters (NP size < 2 nm) as a support of Au-based electrocatalysis, but also offers a superior electrocatalyst to replace Pt-based ones for glycerol oxidation reaction in glycerol fuel-based direct alcohol fuel cells.
A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of the multiwall carbon nanotubes (MWCNTs) by π–π stacking interaction between naphthalen-1-ylmethylphosphonic acid (NYPA) and MWCNTs. Noncovalently attachment of phosphonate groups on the MWCNTs surface is confirmed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and zeta potential analysis. The water-soluble phosphonate functionalized MWCNTs are further deposited with Pd nanoparticles (Pd-NPs) as electrocatalyst for formic acid oxidation. The morphology and structure of Pd-MWCNTs nanocomposites are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and XPS measurements. It is observed that Pd-NPs are highly dispersed and effectively anchored on the side walls of the phosphonate functionalized MWCNTs. The Pd-MWCNTs nanocomposites exhibit better electrocatalytic activity and long-term stability for formic acid electrooxidation than the un-phosphonated counterpart.
