Kennedy, Brendan - University of Sydney

研究领域

Solid State and Materials Chemistry Crystallography - X-ray and Neutron Scattering Structure and Bonding in Metal Oxides Structural phase transitions in perovskite oxides: Perovskites are arguably the most important class of metal oxides. We are using a combination of high resolution synchrotron and neutron diffraction studies to understand the response of perovskites to external stimuli, especially temperature and pressure. The delicate balance of simple factors such as ionic size and the degree of covalency of the cations leads to a rich variety of behavior in perovskite oxides. Some phase transitions simply involve tilting of the octahedral structural units in the crystal, while others, such as SrBi2Ta2O9, produce a ferroelectric form, which are of considerable scientific and technological importance. Heavy metals in inorganic hosts: Bone and teeth contain a large amount of a calcium hydroxy phosphate isostructural with the mineral apatite, Ca10(PO4)6(OH)2. We are interested in the interaction of such minerals with toxic heavy metals such as Pd or Cd in order to understand the fate of these metals in both the body and environment. This work explores the structural response of minerals to a variety of heavy metals. Valence states in mixed 3d and 4d oxides: Replacing Sr with Ca in the mixed metal oxide SrRu0.5Mn0.5O3 induces a first order phase transition associated with the loss of the Jahn-Teller distortion of the Mn3+ cation. Or so the story goes. Analysis of the formal oxidation states of the Mn and Ru suggests complex redox equilibrium exists and that the Ca reduces the extent of electron transfer from the Ru to the Mn. This results in both cations having a non-integer oxidation state. The challenge is to quantify this using spectroscopic methods and suitable standards. Oxides for solid state memory devices: Ferroelectric oxides are being targeted for use in non-volatile memory devices. We are working to extend the family of layered bismuth oxides that may be suitable for this application. Bi4Ti3O12 is an attractive alternative to PbZr0.5Ti0.5O3 in ferroelectric devices, both since it does not contain any toxic lead and because of its large spontaneous polarization. Substitution of both the Bi and Ti cations is likely to alter the polarization and this project will explore the synthesis, structure and properties of layers oxides such as Bi3SrNaNb3O12 and Bi2Sr2Nb2.67Zn0.33O12 as alternatives to Bi4Ti3O12. Variable temperature structural studies are critical to establish the impact these substitutions have on the stability of the ferroelectric mode.

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Blanchard, P., Chapman, K., Heald, S., Zbiri, M., Johnson, M., Kennedy, B., Ling, C. (2016). Direct observation of pressure-driven valence electron transfer in Ba₃BiRu₂O₉, Ba₃Bilr₂O₉, and Ba₄Bilr₃O1₂. Inorganic Chemistry, 55(11), 5649-5654. [More Information] Saha, R., Fauth, F., Avdeev, M., Kayser, P., Kennedy, B., Sundaresan, A. (2016). Magnetodielectric effects in A-site cation-ordered chromate spinels LiMCr4O8 (M = Ga and In). Physical Review B, 94(6), 064420-1-064420-9. [More Information] Marini, C., Noked, O., Kantor, I., Joseph, B., Mathon, O., Shuker, R., Kennedy, B., Pascarelli, S., Sterer, E. (2016). Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3. Journal of Physics: Condensed Matter, 28(4), 1-8. [More Information] William Arulnesan, S., Kayser, P., Kennedy, B., Kimpton, J., Knight, K. (2016). Phase separation in NaTaO3. Impact of temperature and doping. Solid State Sciences, 52, 149-153. [More Information] Kennedy, B., Avdeev, M., Feng, H., Yamaura, K. (2016). Phase transitions in strontium perovskites. Studies of SrOsO3 compared to other 4d and 5d perovksites. Journal of Solid State Chemistry, 237, 27-31. [More Information] Reynolds, E., Kennedy, B., Avdeev, M., Thorogood, G., Zhang, Z., Brand, H. (2016). Structural and spectroscopic studies of Ba2Y1-deltaUO6+x. Journal of Solid State Chemistry, 243, 8-11. [More Information] Murphy, G., Kennedy, B., Johannessen, B., Kimpton, J., Avdeev, M., Griffith, C., Thorogood, G., Zhang, Z. (2016). Structural studies of the rhombohedral and orthorhombic monouranates: CaUO4, alpha-SrUO4, beta-SrUO4 and BaUO4. Journal of Solid State Chemistry, 237, 86-92. [More Information] Shafique, M., Kennedy, B., Iqbal, Y., Ubic, R. (2016). The effect of B-site substitution on structural transformation and ionic conductivity in Ho2(ZryTi1-y)2O7. Journal of Alloys and Compounds, 671, 226-233. [More Information] William Arulnesan, S., Kayser, P., Kennedy, B., Knight, K. (2016). The impact of room temperature polymorphism in K doped NaTaO3 on structural phase transition behaviour. Journal of Solid State Chemistry, 238, 109-112. [More Information] Austin, C., Smith, T., Mostofi Zadeh Farahani, R., Hinde, K., Carter, E., Lee, J., Lay, P., Kennedy, B., Sarrafpour, B., Wright, R., Arora, M., et al (2016). Uncovering system-specific stress signatures in primate teeth with multimodal imaging. Scientific Reports, 6, 1-11. [More Information] Wang, C., Avdeev, M., Kennedy, B., Kupers, M., Ling, C. (2016). YCa3(CrO)3(BO3)4: A Cr3+ kagome lattice compound showing no magnetic order down to 2 K. Inorganic Chemistry, 55(15), 7535-7541. [More Information] Ranjbar, B., Kennedy, B. (2015). Anisotropic thermal expansion in Sr2RhO4 - A variable temperature synchrotron X-ray diffraction study. Solid State Sciences, 49, 43-46. [More Information] Liu, S., Blanchard, P., Zhang, Z., Kennedy, B., Ling, C. (2015). Long- and short-range structure studies of KBT-KBZ solid-solutions using synchrotron radiation. Dalton Transactions, 44(23), 10681-10688. [More Information] Kennedy, B., Qasim, I., Knight, K. (2015). Low temperature structural studies of SrSnO3. Journal of Physics: Condensed Matter, 27(36), 365401-1-365401-5. [More Information] Rao, B., Avdeev, M., Kennedy, B., Ranjan, R. (2015). Phase boundary at x = 0.03 and its anomalous influence on the structure and properties in the lead-free piezoelectric (1-x)Na1/2Bi1/2TiO3-(x)BaTiO3. Physical Review B, 92(21), 214107-1-214107-11. [More Information] Knight, K., Kennedy, B. (2015). Phase coexistence in NaTaO3 at room temperature; a high resolution neutron powder diffraction study. Solid State Sciences, 43, 15-21. [More Information] Ranjbar, B., Reynolds, E., Kayser, P., Kennedy, B., Hester, J., Kimpton, J. (2015). Structural and magnetic properties of the iridium double perovskites Ba2-xSrxYIrO6. Inorganic Chemistry, 54(21), 10468-10476. [More Information] Ranjbar, B., Pavan, A., Kennedy, B., Zhang, Z. (2015). Structural and magnetic properties of the ruthenium double perovskites Ba2-xSrxYRuO6. Dalton Transactions, 44(23), 10689-10699. [More Information] Reynolds, E., Thorogood, G., Avdeev, M., Brand, H., Gu, Q., Kennedy, B. (2015). The role of pi-bonding on the high temperature structure of the double perovskites Ba2CaUO6 and BaSrCaUO6. Dalton Transactions, 44(36), 16036-16044. [More Information] Ranjbar, B., Kennedy, B. (2015). Unusual thermal expansion of Sr2IrO4: A variable temperature synchrotron X-ray diffraction study. Journal of Solid State Chemistry, 232, 178-181. [More Information]