Browsing by Author "Yao, SH"

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    Lattice dynamics of KxRhO2 single crystals
    (AIP Publishing, 2015-08-05) Zhang, BB; Zhang, NN; Dong, ST; Lv, YY; Chen, YB; Yao, SH; Zhang, ST; Gu, ZB; Zhou, J; Guedes, I; Yu, DH; Chen, YF
    A series of crystals KxRhO2 (x = 0.72, 0.63, 0.55, 0.39, and 0.24) have been synthesized and their vibrational properties have been studied by first principles calculations, Raman spectroscopy, and inelastic neutron scattering. The measured vibrational spectra of KxRhO2 for x = 0.72 and 0.63 are consistent with the theoretical prediction for the stoichiometric KRhO2. For samples with x = 0.55, 0.39 and 0.24, extra vibrational modes have been observed and they are believed to be due to the symmetry reduction and the loss of translational symmetry induced by K disorder. The good agreement was found for the phonon density of states among the Raman spectroscopic observations, inelastic neutron scattering and the first principles calculations, as an evidence for the generation of structure disorder by K deficiency. © 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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    Low temperature neutron diffraction on congruent and near stoichiometric LiNbO3
    (World Scientifice Publishing Company, 2012-08-30) Yao, SH; Sang, YH; Yu, DH; Avdeev, M; Liu, H; Wang, JY; Zhang, NN
    Neutron powder diffraction has been carried out on a congruent LiNbO(3) sample containing (7)Li isotope (C(7)LN) and a near stoichiometric Mg doped LiNbO3 sample (Mg: NSLN) in the temperature range of 4 K and 90 K. Large anisotropic displacement parameters (ADPs) of the Li ions have shown evidence of large disorder along the c-axis for both samples. The results have shown no evidence for the existence of anomalous structural behavior for both samples at low temperatures, although abnormal structural features at 55 K and 100 K for a LiNbO3 crystal having different Li content as the samples used in the present studies have been observed by Fernandez-Ruiz et al. [Phys. Rev. B 72 (2005) 184108]. © 2012, World Scientific Publishing Co.
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    Mechanism of the abnormal thermal expansion of nearly stoichiometric LiNbO3
    (Elsevier Science, 2011-03-01) Yao, SH; Wang, JY; Liu, HB; Yan, T; Yu, DH; Chen, YF
    High temperature X-ray diffraction, thermal expansion and Raman spectroscopic measurements have been conducted to investigate the structural behavior of nearly stoichiometric LiNbO3. Abnormal thermal expansion has been observed within the temperature range of 1021-1373 K. The mechanism responsible for the abnormal phenomena and the structure deformation has been identified as the competition between the thermal vibration in the x-y plane and the antiphase motion along the z-axis of the [NbO6] framework as a function of temperature through the analysis of the temperature dependent Raman spectra. (C) 2010 Elsevier B.V.
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    The physical mechanism of extremely low thermal conductivity of BiCuTeO and BiCuSeO revealed by inelastic neutron and Raman spectroscopy
    (Elsevier, 2020-06-15) Lin, D; Dong, ST; Zhang, YY; Lv, YY; Zhou, J; Chen, YB; Mole, RA; Yao, SH; Yu, DH
    Layered structure BiCuSeO-based compounds have extremely low thermal conductivity about ∼0.5–0.8 W/m·K, and the corresponding physical origin has been extensively studied by the first-principles calculations. Here we experimentally revealed the physical mechanism of extremely low thermal conductivity in BiCuSeO and BiCuTeO through inelastic neutron and Raman scattering spectroscopy. Generalized phonon density of states (PDOS) characterized by inelastic neutron scattering reveals that the average acoustic-phonon velocities of BiCuSeO and BiCuTeO are as low as 2104 and 1547 m/s, respectively, which are lower than most of normal materials (∼3000 m/s), and strong anharmonic effect in BiCuSeO and BiCuTeO. Strongly anharmonic effect is also verified by the large Grüneisen constant of specific optical-phonon mode of BiCuSeO and BiCuTeO (∼6.7 in BiCuTeO). The calculated thermal conductivities of BiCuSeO and BiCuTeO by phenomenological thermal conductivity formula, under approximation of the relaxation-time as minimum quasi-particle lifetime of optical-phonon mode, are close to experimental values. Our work sheds more light on the physical mechanism of extremely low thermal conductivity in these compounds. © 2020 Elsevier B.V.