Browsing by Author "Sang, YH"

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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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    X-ray and neutron diffraction studies of flux and hydrothermally grown nonlinear optical material KBe2BO3F2
    (Royal Society of Chemistry, 2012-01-01) Sang, YH; Yu, DH; Avdeev, M; Piltz, RO; Sharma, N; Ye, N; Liu, H; Wang, JY
    Deep-UV nonlinear optical material KBe2BO3F2 (KBBF), fabricated by flux and hydrothermal methods, are studied by single crystal and powder X-ray diffraction (XRD) and neutron diffraction (NPD). Based on the single crystal diffraction data, the standard R32 structure is confirmed for flux grown KBBF, while the R $(3) over bar $c structure is identified for the hydrothermally grown KBBF. No clear evidence of hydrogen bonding is found in the crystals by single crystal neutron diffraction. From powder XRD and neutron diffraction, the hydrothermally grown KBBF under investigation is found to be a mixture of two components consisting of 19.8 wt% of the R32 structure and 80.2 wt% of the R $(3) over bar $c structure. No phase changes as a function of temperature up to 775 degrees C are observed for both samples from temperature dependent powder XRD data. However, a large anisotropic thermal expansion of the lattice is shown in the temperature dependent data. © 2012, Royal Society of Chemistry.
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    X-ray and neutron diffraction studies of flux and hydrothermally grown nonlinear optical material KBe2BO3F2
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-07) Sang, YH; Yu, DH; Avdeev, M; Piltz, RO; Sharma, N; Wang, JY
    KBe2BO3F2 (KBBF) has been known as one of the most important nonlinear optical (NLO) crystals. It is the only NLO crystal which can be used directly in deep ultraviolet (DUV) harmonic generation. Laser radiations of 186.3—200 nm and 156 nm have been generated with KBBF crystals. KBBF single crystals can be grown by either flux or hydrothermal methods. Flux-grown (flux-KBBF) crystals have good harmonic generation efficiency with very small crystal size. Though larger crystals can be obtained from hydrothermal method, such crystals (hydro-KBBF) have very low harmonic generation efficiency. In order to understand the reason for the differences between flux and hydrothermal grown crystals, we carried out comparative single crystal X-ray diffractions (XRD) and neutron diffraction (ND) experiments on both hydro- and flux-KBBF single crystals. We also investigate their components with powder XRD and ND, as well as their temperature-dependent behaviours to characterise possible phase transitions. Single crystal XRD and ND data have confirmed the R32 structure for the flux-KBBF and R-3c structure for the hydro-KBBF samples. While the R32 structure is still valid for the flux-KBBF from powder diffraction data, a mixture of 80.2 wt% of the R-3c structure and 19.8 wt% of the R32 structure was found for the hydro-KBBF. This finding may explain the low harmonic generation efficiency from the hydro-KBBF as the central-symmetric R-3c component should not contribute to the harmonic generation at all. Temperature dependent XRD did not reveal any phase transition between the R32 and R-3c structures, though the growth temperature for hydro-KBBF is significantly lower than that for flux-KBBF. The current single crystal neutron diffraction did not find evidence of the presence of any hydrogen bond which was originally considered as the force responsible for the formation of large crystals.
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    Yttrium aluminum garnet nanoparticles with low antisite defects studied with neutron and x-ray diffraction
    (Academic Press Inc Elsevier Science, 2012-08-01) Sang, YH; Yu, DH; Avdeev, M; Qin, HM; Wang, JY; Liu, H; Lv, YH
    The presence of cation antisite defects is considered to be one of the most important factors determining the fluorescence, laser, and scintillation properties of rare earth-doped yttrium aluminum garnet(YAG) materials. However, no direct evidence or systematic investigation of antisite defect evolution as a function of cation composition variation in YAG has been reported in the previous literature. In this paper, we report a combined neutron and X-ray diffraction investigation on cation antisite defects performed on specially synthesized nonstoichiometric yttrium aluminum garnet nanoparticles to try to understand the defect chemistry in the YAG system. No evidence was found for Y(Al,16a), Y(Al.24d) and Al(Y.24C) antisite defects in these specially fabricated samples within the limit of diffraction techniques. The results suggest that YAG materials containing low level or no antisite defects can be achieved through low temperature synthesis process. © 2012, Elsevier Ltd.