Browsing by Author "Porter, SH"

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    Structural and magnetic properties of RTiNO2 (R=Ce, Pr, Nd) perovskite nitride oxides
    (Elsevier, 2015-03-01) Porter, SH; Huang, ZG; Cheng, ZX; Avdeev, M; Chen, ZX; Dou, SX; Woodward, PM
    Neutron powder diffraction indicates that CeTiNO2 and PrTiNO2 crystallize with orthorhombic Pnma symmetry (Ce: a=5.5580(5), b=7.8369(7), and c=5.5830(4) Å; Pr: a=5.5468(5), b=7.8142(5), and c=5.5514(5) Å) as a result of a–b+a– tilting of the titanium-centered octahedra. Careful examination of the NPD data, confirms the absence of long range anion order in both compounds, while apparent superstructure reflections seen in electron diffraction patterns provide evidence for short range anion order. Inverse magnetic susceptibility plots reveal that the RTiNO2 (R=Ce, Pr, Nd) compounds are paramagnetic with Weiss constants that vary from −28 to −42 K. Effective magnetic moments for RTiNO2 (R=Ce, Pr, Nd) are 2.43 μB, 3.63 μB, and 3.47 μB, respectively, in line with values expected for free rare-earth ions. Deviations from Curie–Weiss behavior that occur below 150 K for CeTiNO2 and below 30 K for NdTiNO2 are driven by magnetic anisotropy, spin–orbit coupling, and crystal field effects. © 2015 Elsevier Inc.
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    Structural, magnetic, and optical properties of A3V4(PO4)6 (A = Mg, Mn, Fe, Co, Ni)
    (American Chemical Society, 2016-05-26) Porter, SH; Xiong, J; Avdeev, M; Merz, D; Woodward, PM; Huang, Z
    Combined synchrotron and neutron powder diffraction indicates that A3V4(PO4)6 (A = Mg, Mn, Fe, Co, Ni) compounds crystallize with triclinic P1̅ symmetry. Lattice parameters expand as expected with successive increases in the ionic radius of the A2+ ion. Cation disorder on the octahedral sites increases as the ionic radii of A2+ ion decreases. Direct-current magnetic susceptibility measurements indicate that all compounds with magnetic A2+ ions order anti-ferromagnetically with transition temperatures ranging from 12 to 15 K. Effective magnetic moments for A3V4(PO4)6 (A = Mg, Mn, Fe, Co, Ni) are 5.16, 11.04, 10.08, 9.76, and 7.96 μB per formula unit, respectively, in line with calculated values for high-spin transition metal ions. With the exception of Co3V4(PO4)6 the ultraviolet–visible spectra are dominated by d–d transitions of the V3+ ions. The striking emerald green color of Co3V4(PO4)6 arises from the combined effects of d–d transitions involving both V3+ and Co2+. © 2016 American Chemical Society