Ilyas Qasim

Low temperature structural studies of SrSnO3.

High resolution powder neutron diffraction measurements on polycrystalline SrSnO3 between 8 and 350 K are described. SrSnO3 retains the orthorhombic Pbnm structure over this temperature range. Examination of the thermal expansion of the individual lattice parameters reveals an anomaly near 230 K that may reflect the presence of polar nanodomains associated with local disorder of the octahedral tilts.

Synthesis, structures and properties of transition metal doped SrIrO3

The synthesis of some transition metal SrIr1−xMxO3 type oxides is described. These have an orthorhombic perovskite type-structure and are only found when the formal oxidation state of the Ir is approximately equal to +4.5 and for M = Fe, Co, Ni and Zn. Occupancy of the TM eg type orbitals appears to contribute to the break-down of the dimeric motif seen in the 6H–SrIrO3 structure. Variable temperature resistivity measurements show that SrIr0.8Zn0.2O3 is a metal; SrIr0.8Ni0.2O3 an non-metal and SrIr0.8Co0.2O3 undergoes a temperature dependent metal–insulator transition.

X-ray absorption near edge structure and crystallographic studies of the mixed valence oxide SrRu0.8Ni0.2O3

Neutron diffraction methods are used to refine the structure of SrRu(0.8)Ni(0.2)O(3) at room temperature and 4 K. X-ray absorption measurements at the Ru L-edge demonstrate that partial oxidation of the Ru(4+) to Ru(5+) occurs upon introducing Ni into the SrRuO(3) structure to form SrRu(0.8)Ni(0.2)O(3). Whilst the diffraction measurements show that SrRu(0.8)Ni(0.2)O(3) is isostructural with SrRuO(3), the Ni doped compound exhibits an unusual first order orthorhombic-cubic phase transition near 670 K as revealed by x-ray diffraction. The Curie temperature in SrRu(0.8)Ni(0.2)O(3) is lower than that found in SrRuO(3) as a consequence of local distortions reducing the p-d hybridization.

Synchrotron X-Ray Powder Diffraction Studies of Structural Phase Transitions in Perovskite Oxides

The utilization of the high resolution powder diffractometer at the Australian Synchrotron to obtain accurate and precise structures of some perovskite-type oxides is described. The structure of CdTiO3 has been studied from room temperature to 1000°C by high-resolution synchrotron X-ray powder diffraction. It was found that CdTiO3 remains orthorhombic in the Pbnm space group over the entire temperature range, with the expansion in the cell volume well fitted to the expression . The magnitudes of the TiO6 tilts are estimated from the refined structural parameters and these progressively reduce as the temperature is increased. The effect of Sr content on the room temperature structure of the double perovskites Ba2–xSrxInTaO6 is also described. At room temperature Ba2InTaO6 crystallizes in a cubic structure in space group . Doping with Sr results in tilting of the corner sharing octahedra with a concurrent lowering of symmetry with the sequence of structures being

Impact of Cu Doping on the Structure and Electronic Properties of LaCr1–yCuyO3

Oxides of the type LaCr(1-y)Cu(y)O3 have been prepared using solid-state methods and their crystal structures refined using synchrotron X-ray powder diffraction. The solubility limit of Cu was found to be around y = 0.2, and such oxides are orthorhombic in space group Pbnm. X-ray absorption spectroscopy measurements at the Cr and Cu L-edges demonstrated that the Cr remains trivalent upon Cu doping, with the Cu being present as Cu(III). The oxides are found to be antiferromagnets, and the Néel temperature, TN, decreases as the Cu content is increased. The crystal and magnetic structures of one example La(Cr0.85Cu0.15)O3 have been investigated between 3 and 350 K by neutron powder diffraction. The samples are semiconductors.

Stabilising the orthorhombic perovskite structure in SrIrO3 through chemical doping. Synthesis, structure and magnetic properties of SrIr1−xMgxO3(0.20 ≤ x ≤ 0.33)

The synthesis, structure, magnetic and electric conductivity properties of Mg doped SrIrO3 are described. Doping SrIrO3 with Mg favours an orthorhombic structure over the hexagonal face-sharing structure. Polycrystalline samples of the type SrIr1−xMgxO3 with an orthorhombic perovskite-type structure have been formed for 0.2 < x < 0.33. At x = 0.2 the formal oxidation state of the Ir is +4.5 and the material displays metallic conductivity. At x = 0.33 the Ir is in the +5 state and the material is non-metallic. Magnetic susceptibility measurements demonstrate the materials to be spin-glasses in which short range ferromagnetic interactions are evident.

Structural and electronic properties of Sr{sub 1−x}Ca{sub x}Ti{sub 0.5}Mn{sub 0.5}O{sub 3}

Abstract The series of Sr1−xCaxTi1/2Mn1/2O3 perovskites has been prepared using solid state methods and their structures determined using combination of synchrotron X-ray and powder neutron diffraction. At room temperature the crystal structure evolves with increasing Ca content from P m 3 ¯ m →tetragonal I4/mcm→orthorhombic Pbnm, as a consequence of the sequential introduction of cooperative tilting of the (Ti/Mn)O6 octahedra. X-ray absorption measurements show the Mn is tetravalent in all oxides. Magnetic susceptibility measurements demonstrate all the oxides to be paramagnetic at room temperature, with a transition to a spin glass arrangement occurring at low temperatures. Electrical measurements prove that all the members are semiconductors and their activation energy increase with Ca doping amount.

Soft ferromagnetism in mixed valence Sr(1-x)La(x)Ti(0.5)Mn(0.5)O₃ perovskites.

The structural, magnetic and electrical properties of the mixed Ti-Mn oxides Sr(1-x)La(x)Ti(0.5)Mn(0.5)O3 (0 ≤ x ≤ 0.5) are reported. At room temperature the oxides have a cubic structure in space group Pm3m for x ≤ 0.25 and rhombohedral in R3c for 0.3 ≤ x ≤ 0.50. X-ray absorption spectroscopic measurements demonstrate the addition of La(3+) is compensated by the partial reduction of Mn(4+) to Mn(3+). Variable temperature neutron diffraction measurements show that cooling Sr(0.6)La(0.4)Ti(0.5)Mn(0.5)O3 results in a first order transition from rhombohedra to an orthorhombic structure in Imma. Complex magnetic behaviour is observed. The magnetic behaviour of the mixed valent (Mn(3+/4+)) examples is dominated by ferromagnetic interactions, although cation disorder frustrates long range magnetic ordering.

Structural characterization of the perovskite series Sr{sub 1−x}La{sub x}Ti{sub 0.5}Mn{sub 0.5}O{sub 3}

The perovskite-type compounds Sr{sub 1−x}La{sub x}Ti{sub 0.5}Mn{sub 0.5}O{sub 3}, x=0, 0.1, 0.2, 0.3, 0.4 and 0.5 have been synthesized by solid-state methods, and their room temperature structures determined using X-ray synchrotron powder diffraction. The x=0.0 end member, SrMn{sub 0.5}Ti{sub 0.5}O{sub 3} is cubic in space group Pm3{sup ¯}m; there being no evidence for ordering of the Ti{sup 4+} and Mn{sup 4+} cations. We find that x=0.5 compound is rhombohedral in R3{sup ¯}c rather than orthorhombic as reported previously. Magnetic measurements suggest that both SrMn{sub 0.5}Ti{sub 0.5}O{sub 3} and Sr{sub 0.5}La{sub 0.5}Mn{sub 0.5}Ti{sub 0.5}O{sub 3} are spin-glasses. - Graphical abstract: A cubic–rhombohedral phase-transition is observed cation disordered perovskites Sr{sub 1−x}La{sub x}Ti{sub 0.5}Mn{sub 0.5}O{sub 3}. Both end members are spin-glasses. Highlights: ► Structural studies of Sr{sub 1−x}La{sub x}Ti{sub 0.5}Nb{sub 0.5}O{sub 3} perovskites, show lack of long range Mn:Ti order. ► Magnetic properties indicative of spin-glass behavior. ► Changes of crystal structure from cubic to rhombohedral with increasing lanthanum content.