NDLI: On the evolution of the $DyNiO_{3}$ perovskite across the metal–insulator transition though neutron diffraction and Mössbauer spectroscopy studies

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Fernández-díaz, M. T. Martínez-lope, M. J. Demazeau, G. Presniakov, I. A. Rusakov, V. S. Alonso, J. A. Sobolev, A. V. Gubaidulina, T. V.
Description	Author Affiliation: Alonso JA ( Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, E-28049 Madrid, Spain. ja.alonso@icmm.csic.es)
Abstract	The structural changes of polycrystalline $DyNiO_{3}$ perovskite across the metal–insulator transition $(T_{MI}$ = 564 K) have been studied by high resolution neutron diffraction techniques together with Mössbauer spectroscopy , in a sample doped with 1.5 at.% $^{57}Fe.$ In the insulating (semi-conducting) regime, below $T_{MI},$ the perovskite is monoclinic, space group (SG) $P2_{1}/n,$ and the crystal structure contains two chemically different Ni1 and Ni2 cations , as a result of the charge disproportionation of $Ni^{3+}$ cations . The β parameter, characterizing the low-temperature monoclinic distortion, is smaller than 90.04° for T < $T_{MI},$ indicating a strongly pseudo-orthorhombic symmetry, although the internal monoclinic symmetry, implying the splitting and shifts of oxygen positions around the two Ni sites is perfectly detected by neutrons . Above $T_{MI},$ $DyNiO_{3}$ becomes orthorhombic, SG Pbnm. Upon heating across $T_{MI},$ there is an abrupt convergence of the two sets (Ni1 and Ni2) of three Ni–O bond lengths, in the monoclinic-insulating phase, to three unique Ni–O distances in the orthorhombic-metallic phase upon entering the metallic region. The $^{57}Fe$ Mössbauer spectra of an iron-doped (1.5 at.%) $DyNiO_{3}$ sample recorded in the insulating, paramagnetic temperature range $(T_{N}$ < T < $T_{MI})$ are discussed by supposing that the $Fe^{3+}$ probe cations replace nickel in the two octahedral Ni1 and Ni2 sites. Electric field gradient calculations have shown that the $^{57}Fe$ hyperfine parameters of Fe1 and Fe2 subspectra reflect a specificity of local structure corresponding to large $(Ni1O_{6})$ and small $(Ni2O_{6})$ octahedra. At T > $T_{MI},$ the $^{57}Fe$ spectrum gives clear evidence for the formation of an unique state for iron probe atoms and could, therefore, imply that the charge disproportionation in the $(NiO_{6})$ subarray completely vanishes at the insulator→metal transition.
ISSN	14779226
Journal	Dalton Trans.
Issue Number	46
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2008-12-14
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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