Browsing by Author "Singh, DJ"

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    Antiferromagnetism in a technetium oxide. Structure of CaTcO3
    (American Chemical Society, 2011-01-16) Avdeev, M; Thorogood, GJ; Carter, ML; Kennedy, BJ; Ting, J; Singh, DJ; Wallwork, KS
    The technetium perovskite CaTcO3 has been synthesized. Combining synchrotron X-ray and neutron diffraction, we found that CaTcO3 is an antiferromagnetic with a surprisingly high Neel temperature of ~800 K. The transition to the magnetic state does not involve a structural change, but there is obvious magnetostriction. Electronic structure calculations confirm the experimental results. © 2011, American Chemical Society
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    Characterisation of Pb2Rh2O7 and Y2Rh2O7: an unusual case of pyrochlore stabilisation under high pressure, high temperature synthesis conditions
    (Royal Society of Chemistry (RSC), 2024-02-01) Injac, SD; Mullens, BG; Romero, FD; Avdeev, M; Barnett, C; Yuen, AKL; Patino, MA; Mukherjee, S; Vaitheeswaran, G; Singh, DJ; Kennedy, BJ; Shimakawa, Y
    Two novel oxides with Pb2Rh2O7 and Y2Rh2O7 compositions were synthesised using high pressure, high temperature techniques at 19 GPa and 8 GPa, respectively. Structurally, both compounds were determined to crystallise in the cubic pyrochlore structure, space group Fd[3 with combining macron]m, with no observed oxygen vacancies. Both oxides have effectively identical Rh–O bond lengths of 1.987 Å and a bond-valence sum (BVS) of 4.2 that confirm a Rh4+ oxidation state. Physical property measurements for Pb2Rh2O7 are consistent with a metallic ground state. This is similar to other Pb2M2O7 oxides where M = Ru, Ir, and Os. Y2Rh2O7 represents an unusual case of the lower density (6.356 g cm−3) pyrochlore structure being stabilised under high pressure conditions, while the analogous, higher density (7.031 g cm−3) perovskite YRhO3 is stabilised by synthesis under ambient pressure conditions. The Rh4+ state results in a S = ½ magnetic ground state. Magnetisation measurements suggest strong AFM coupling in Y2Rh2O7. However, long range AFM order is not observed down to 2 K presumably due to the geometric frustration of the pyrochlore lattice. Specific heat and resistivity measurements indicate a large electronic contribution to the heat capacity. The Wilson ratio of 4.78(11) is well above 2, indicating nearness to magnetism and the likely presence of Rh moments in the background of the conduction electrons. Catalytic activity indicated a greater correlation with other Rh pyrochlores as opposed to dependence on the Rh oxidation state. Facebook Twitter LinkedIn YouTube © Royal Society of Chemistry
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    High temperature magnetic ordering in the 4d perovskite SrTcO3
    (American Physical Society, 2011-02-07) Rodriguez, EE; Poineau, F; Llobet, A; Kennedy, BJ; Avdeev, M; Thorogood, GJ; Carter, ML; Seshadri, R; Singh, DJ; Cheetham, AK
    We present evidence for possibly the highest magnetic ordering temperature in any compound without 3d transition elements. Neutron powder diffraction measurements, at both time-of-flight and constant wavelength sources, were performed on two independently prepared SrTcO3 powders. SrTcO3 adopts a distorted perovskite structure with G-type antiferromagnetic ordering and has a moment of 1.87(4)μB per Tc cation at room temperature with an extraordinarily high Néel point close to 750°C. Electronic structure calculations reveal extensive mixing between the technetium 4d states and oxygen states proximal to the Fermi level. This hybridization leads to a close relationship between magnetic ordering temperature and moment formation in SrTcO3. © 2011, American Physical Society