Browsing by Author "Huang, Z"

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    “114”-Type nitrides LnAl(Si4−xAlx)N7Oδ with unusual [AlN6] octahedral coordination
    (Wiley, 2017-02-28) Huang, S; Huang, Z; Cao, P; Zujovic, Z; Price, JR; Avdeev, M; Que, M; Suzuki, F; Kido, T; Ouyang, X; Kaji, H; Fang, M; Liu, YG; Gao, W; Söhnel, T
    Aluminum–nitrogen six-fold octahedral coordination, [AlN6], is unusual and has only been seen in the high-pressure rocksalt-type aluminum nitride or some complex compounds. Herein we report novel nitrides LnAl(Si4−xAlx)N7Oδ (Ln=La, Sm), the first inorganic compounds with [AlN6] coordination prepared via non-high-pressure synthesis. Structure refinements of neutron powder diffraction and single-crystal X-ray diffraction data show that these compounds crystallize in the hexagonal Swedenborgite structure type with P63mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagomé layers of [SiN4] tetrahedra. Solid-state NMR data of high-purity La-114 powders confirm the unusual [AlN6] coordination. These compounds are the first examples of the “33-114” sub-type in the “114” family. The additional site for over-stoichiometric oxygen in the structure of 114-type compounds was also identified. © 1999-2021 John Wiley & Sons, Inc.
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    Complex 5d magnetism in a novel S= 1/2 trimer system, the 12L hexagonal perovskite ba4biir3o12
    (American Chemical Society, 2013-10-21) Miiller, W; Dunstan, MT; Huang, Z; Mohamed, Z; Kennedy, BJ; Avdeev, M; Ling, CD
    The 12L hexagonal perovskite Ba4BiIr3O12 has been synthesized for the first time and characterized using high-resolution neutron and synchrotron X-ray diffraction as well as physical properties measurements. The structure contains Ir3O12 linear face-sharing octahedral trimer units, bridged by corner-sharing BiO6 octahedra. The average electronic configurations of Ir and Bi are shown to be +4(d5) and +4(s1), respectively, the same as for the S = 1/2 dimer system Ba3BiIr2O9, which undergoes a spin-gap opening with a strong magnetoelastic effect at T* = 74 K. Anomalies in magnetic susceptibility, heat capacity, electrical resistivity, and unit cell parameters indeed reveal an analogous effect at T* ≈ 215 K in Ba4BiIr3O12. However, the transition is not accompanied by the opening of a gap in spin excitation spectrum, because antiferromagnetic coupling among S = 1/2 Ir4+ (d5) cations leads to the formation of a S = 1/2 doublet within the trimers, vs S = 0 singlets within dimers. The change in magnetic state of the trimers at T* leads to a structural distortion, the energy of which is overcompensated for by the formation of S = 1/2 doublets. Extending this insight to the dimer system Ba3BiIr2O9 sheds new light on the more pronounced low-temperature anomalies observed for that compound. © 2013, American Chemical Society.
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    Experimental observation and computational study of the spin-gap excitation in Ba3BiRu2O9
    (American Physical Society, 2016-11-01) Ling, CD; Huang, Z; Kennedy, BJ; Rols, S; Johnson, MR; Zbiri, M; Kimber, SAJ; Hudspeth, J; Adroja, DT; Rule, KC; Avdeev, M; Blanchard, PER
    Ba3BiRu2O9 is a 6H-type perovskite compound containing face-sharing octahedral M2O9 (M=Ir, Ru) dimers, which are magnetically frustrated at low temperatures. On cooling through T∗=176 K, it undergoes a pronounced magnetostructural transition, which is not accompanied by any change in space group symmetry, long-range magnetic ordering, or charge ordering. Here, we report the first direct evidence from inelastic neutron scattering that this transition is due to an opening of a gap in the excitation spectra of dimers of low-spin Ru4+ (S=1) ions. X-ray absorption spectroscopy reveals a change in Ru-Ru orbital overlap at T∗, linking the emergence of this spin-gap excitation to the magnetostructural transition. Ab initio calculations point to a geometrically frustrated magnetic ground state due to antiferromagnetic interdimer exchange on a triangular Ru2O9 dimer lattice. X-ray total-scattering data rule out long-range magnetic ordering at low temperatures, consistent with this geometrically frustrated model. ©2016 American Physical Society
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    Pressure-induced intersite Bi--M (M=Ru, Ir) valence transitions in hexagonal perovskite
    (Wiley Online Library, 2014-02-24) Huang, Z; Auckett, JE; Blanchard, PER; Kennedy, BJ; Miller, W; Zhou, Q; Avdeev, M; Johnson, MR; Zbiri, M; Garbarino, G; Marshall, WG; Gu, QF; Ling, CD
    Pressure-induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba3+nBiM2+nO9+3n (n=0,1; M=Ir,Ru). These compounds show first-order, circa 1 % volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known. Ab initio calculations suggest that magnetic interactions through very short (ca. 2.6 Å) M[BOND]M bonds contribute to the finely balanced nature of their electronic states. © 2014 Wiley‐VCH.
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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
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    Tuning the giant magnetoelastic transition in Ba3BiIr2O9 and Ba3BiRu2O9
    (IOP Science, 2014-06-17) Huang, Z; Avdeev, M; Kennedy, BJ; Knight, KS; Zhou, Q; Ling, CD
    We have experimentally investigated the effects of pressure on the magnetoelastic transitions associated with the opening of spin-gaps in Ba3BiIr2O9 and Ba3BiRu2O9. For both compounds, reducing the unit cell volume by either external physical and internal chemical pressure was found to reduce the temperature T* of the transition and, to a lesser extent, the magnitude of the associated negative thermal volume expansion. The results yield the latent heat associated with the transitions, −3.34(3) × 102 J mol−1 for Ba3BiIr2O9 and −7.1(5) × 102 J mol−1 for Ba3BiRu2O9. The transition in Ba3BiRu2O9 is significantly more robust than in Ba3BiIr2O9, requiring an order of magnitude higher pressures to achieve the same reduction in T*. The differing responses of the two compounds points to differences between the 4d and 5d metals and hence to the importance of spin-orbit coupling, which is expected to be much stronger in the Ir compound. © 2014, IOP Publishing Ltd.