Browsing by Author "Awin, LA"

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    Influence of water on the structure of anion deficient perovskites AA*(BB*) O 5.5 (A& A*= Sr 2+ or Ba 2+, B*= Sr2+, B= Nb 5+ or Ta 5+)
    (Australian Institute of Nuclear Science and Engineering, 2012-11-09) Awin, LA; Kennedy, BJ; Avdeev, M
    The ordered defect niobates and tantalates perovskites have been extensively investigated, since the mechanism of water interaction and the proton chemical diffusions in the structure are critical in determining the electrical properties of such systems. The title double perovskites have a large concentration of oxygen vacancies in their face centred cubic structures. These vacancies can be occupied by protons creating a high ionic conductivity. In the present work, a new methodology processes for creating oxygen vacancies in the perovskites structure was investigated. Four members with representative formula AA*(B* B)O5.5 where A, A* and B* = Sr2+ or Ba2+and B = Nb5+ or Ta5+ have been successfully synthesised by two general methods. The methods were both solid state reactions but used different slurry medium, namely acetone and deionised water. The oxides were characterised by synchrotron X-ray diffraction, variable temperature X-ray diffraction, thermo gravimetric analysis and for the two samples BaSr2Nb05.5 and BaSr2Ta05.5 neutron powder diffraction. The XRD studies show that all the oxides form a cation ordered double perovskite structure. The thermo analysis measurements demonstrate a weight loss and an unusual thermal expansion upon heating for the compounds. The neutron diffraction patterns of BaSr2Nb05.5 and BaSr2NbO5.5 show a large diffuse background that is indicative of a high diffusion of oxygen vacancies in the structures, which confirms that the possibility of creating the oxygen vacancies by the wet method. Details of this structural study will be presented.
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    Structural and magnetic studies of A site doped LaRh1-xCuxO3(A=Ca2+, Sr2+, Pb2+ and Bi3+)
    (Elsevier Science Ltd, 2012-10-18) Awin, LA; Kennedy, BJ; Avdeev, M
    A site doped Rh perovskites with general formula La0.75A0.25Rh0.7Cu0.3O3 and La0.75A0.25Rh0.5Cu0.5O3 (A=Ca2+, Sr2+, Pb2+and Bi3+) were synthesized by solid-state methods and their crystallographic, magnetic, and electric properties investigated. Doping by divalent cations resulted in much lower cell volumes and octahedral distortions than doping with a trivalent oxide. The Pb2+ and Bi3+ (6s2) doped oxides exhibited the lowest magnetic moments and the highest activation energies. Magnetization curves are indicative of antiferromagnetic behavior. The addition of Ca2+, Sr2+, Pb2+and Bi3+cations to the A-site decreases the conductivity.© 2013, Elsevier Ltd.
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    Structural and magnetic studies of Zn doped LaRh(1-2x)Cu2xO3
    (Trans Tech Publications, 2013-04-10) Awin, LA; Kennedy, BJ; Avdeev, M
    Two series of Zn doped Rh perovskites LaRh1-2xCux ZnxO3 and La0.75Pb0.25Rh1-2xCuxZnxO3 (0≤ x ≤0.25) were synthesised by solid-state methods and their crystallographic, magnetic, and electric properties investigated. Both series have an orthorhombic perovskite-type structure in space group Pbnm. The increase in Zn content has an obvious impact on the electron delocalisation in which the shift in the average valency of Cu and Rh (+2.5 and +3.5) has resulted in a reduction in cell volumes and an increase in the effective magnetic moments. The Curie–Weiss magnetization curves measured between 5-300K are indicative of antiferromagnetism. The addition of Pb to the A- site decreases the conductivity as anticipated. © 2013 Trans Tech Publications