Browsing by Author "Khan, HU"

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    Preparation and high resolution structural studies of LixAg1-xNbO3 lead free piezoelectrics
    (Elsevier, 2018-09-13) Farid, U; Khan, HU; Avdeev, M; Whittle, TA; Kennedy, BJ
    Solid solutions of the type (LixAg1-x)NbO3 with x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.10 have been synthesized by a mixed oxide route. The samples were characterized by synchrotron X-ray diffraction (S-XRD), neutron powder diffraction (NPD) and Raman spectroscopy. Rietveld refinements against both the S-XRD and NPD data show that pure AgNbO3 crystalizes in orthorhombic, Pmc21 space group with a unit cell 2 ap ×2 ap × 4ap (where ap is the fundamental perovskite lattice parameter). The sample with x = 0.10 has rhombohedral R3c symmetry with a 2ap×2ap×12ap unit cell. The composition induced orthorhombic to rhombohedral phase transition starts at x ~ 0.05 and is complete by x ~ 0.07. Both phases are present in the region 0.05 ≤ x ≤ 0.07. The Raman spectra were consistent with the S-XRD and NPD data thereby confirming the onset of the structural phase transition in the region 0.05 ≤ x ≤ 0.07. Temperature dependent S-XRD measurements of AgNbO3 revealed the phase transition sequence to be Pmc21↔~340KPbcm↔~630KCmcm↔~650KP4/mbm↔~880KPm3¯m. © 2018 Elsevier Inc.
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    Structural studies of the high temperature phases of AgTaO3
    (Elsevier, 2018-02-01) Farid, U; Khan, HU; Avdeev, M; Injac, S; Kennedy, BJ
    Abstract: The temperature dependence of the structure of a polycrystalline sample of AgTaO3 has been determined using in-situ Synchrotron X-ray powder diffraction methods. This work finds no evidence for the presence of a monoclinic phase, rather three phase transitions have been identified, namely R3c↔390°CCmcm↔465°CP4/mbm↔580°CPm3̅m. The rhombohedral phase was further studied at room temperature by neutron powder diffraction. The co-existence of the rhombohedral and orthorhombic phases around 380–400 ° C indicates that the transition between these is first order, and gives rise to unusual peak shapes in the diffraction patterns. © 2017 Elsevier Inc.