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Manoj K. Singh Hyun M. Jang H. C. Gupta Ram S. Katiyar 《Journal of Raman spectroscopy : JRS》2008,39(7):842-848
The first‐ and second‐order Raman‐active phonons in the orthorhombic Pbnm NdFeO3 single crystals were studied by means of polarized Raman scattering and lattice dynamics computations (LDC). The zone‐center phonons of Ag symmetry were distinguished from the B1g eigenmodes by performing polarized Raman scattering experiments using two parallel polarization configurations, X′(ZZ)X′ and Z(X′X′)Z. With the help of LDC, we were able to assign most of the observed Raman‐active modes, including phonons of B2g and B3g symmetry. The LDC results indicated that among the 16 force constants employed, the one corresponding to the stretching vibration between the central Fe cation and the axial oxygen atom in a FeO6 octahedron unit had the largest value. This suggests that the B‐site Fe cation is more tightly bound to the axial O1 ion than the other two equatorial O2 ions. It was further shown that at higher wavenumbers, the displacement of oxygen atoms contributed dominantly to the zone‐center vibrations. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Amorphous, nanocrystalline, and bulk AlO(OH) · xH2O crystals have six fundamental modes (FM) of vibration in a nonlinear AlO(OH) molecular structure. Most of them appear in groups of four IR and Raman bands. Their positions and relative intensities differ significantly in three specimens. The nanocrystals (monoclinic structure with z=8 molecules per unit cell) have four OH stretching bands at values enhanced by up to 360 cm−1 at 3120, 3450, 3560 cm−1 in comparison to those in bulk crystals or amorphous specimens. The first two bands are broad, bandwidth Δν1/2200 to 350 cm−1, while the other two are sharp, Δν1/290 cm−1. The sharp bands shift to 3525 and 3595 cm−1 after heating the sample at 100°C. They no longer appear after heating at 300 or 500°C for 2 h (the specimen decomposes to Al2O3), leaving behind only two bands at 3100 and 3400 cm−1. A Δν1/2 value of 500 cm−1 appears in the 3400 cm−1 in a delocalized distribution of H atoms. Two bands also occur at 3098 and 3300 cm−1 in bulk crystals (orthorhombic structure with z=4) or at 2990 and 3515 cm−1 in an amorphous sample. More than one bands appear in a FM vibration in occurrence of sample in more than one conformers. The amorphous sample has approximately the same conformer structure as the bulk crystals. An amorphous surface structure exists in nanocrystals with a group of three bands at 1420, 1510 and 1635 cm−1 in an interconnected network structure. It encapsulates the nanocrystals in an amorphous shell. Its volume fraction, 33% estimated from the integrated intensity in three bands, determines 2.2 nm thickness in the shell in spherical shape of nanocrystals in 35 nm diameter. 相似文献
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We consider here the problem of the existence of a quasi-invariant which is linear in the momenta for Hamiltonians in three
degrees of freedom. We show that such quasi-invariants are more constrained in their structure than in the two degrees of
freedom case. We also show that some of these quasi-invariants have to be interpreted as ‘pseudo-translations’, i.e., as translations
in a non-orthogonal system of coordinates. 相似文献
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Bhogi Jai Rama Satyanarayana Swamy Rangu Vijay Pamidi Ramesh Babu Bhaskar Sanyal Yerramreddy Gandhi Nalluri Veeraiah 《Ionics》2016,22(9):1625-1634
γ-Ray-induced dielectric dispersion in CaF2–B2O3–P2O5 glasses doped with different concentrations of CuO was investigated. The glass samples were exposed to γ-rays with dose varying within the range 0–10 kGy. The dielectric dispersion and spectroscopic properties were measured before and after γ-ray treatment. Additionally, thermoluminescence studies were performed on post-irradiated glass samples. The results of dielectric properties and dielectric breakdown strength indicated a substantial increase in the insulating strength of CuO containing glasses due to γ-ray irradiation. The analysis of these results together with UV-vis optical absorption, IR spectra, and thermoluminescence studies have indicated a gradual increase in the concentration of mono-valent copper ions due to γ-ray treatment of the glass network. The additional studies have confirmed that these Cu+ ions occupy network-forming positions, increase the polymerization of the borophosphate glass network, and facilitates for the increase of insulating strength of the titled glass. 相似文献