X-Ray powder diffraction study of the phase transitions in Ti<sub>4</sub>O<sub>7</sub>

Melzer, R.; Rüscher, Claus H.

doi:10.1080/01411599608241825

Cited by 3 publications

(1 citation statement)

References 16 publications

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“…For pure Fe 2ϩ ions this contribution can be considerable ͑although in most cases it is smaller than the ligand contribution͒, and it is mostly of opposite sign than the ligand contribution. The refined asymmetry parameter, ϭ0.5 (2), is in agreement with the expected deformation ͑stretching͒ of the square-pyramid's basal plane.…”

Section: Mössbauer Studiessupporting

confidence: 67%

Verwey transition in mixed-valenceTbBaFe2O5: Two attempts to order charges

et al. 2001

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Electronic, magnetic, and structural phase transitions in nearly stoichiometric TbBaFe 2 O 5ϩw (0.00Ͻw Ͻ0.05) have been investigated. At high temperatures this compound is a paramagnetic, mixed-valence (Fe 2.5ϩ ) conductor with identical square-pyramidal coordinations at all iron atoms. Upon cooling below T N ϭ450 K, an antiferromagnetic ͑AFM͒ spin order appears, accompanied by a magnetostrictive orthorhombic distortion. At lower temperatures the increasing distortion sets the frame for a first attempt to order charges. Mössbauer spectroscopy shows that one squeezed and one expanded square pyramid appear with different orientations of their magnetic and electric field tensors, each centered by its own mixed-valence iron state, one Fe 2.5ϩ⑀ , the other Fe 2.5Ϫ⑀ . The lattice retains its distortion, but a small, structurally homogeneous, and continuous increase in volume is experienced. At somewhat lower temperature (T V ) a discontinuous increase of the orthorhombic distortion occurs, marking the second attempt to order charges, now with the classical symptoms of the Verwey transition: a large change in volume, entropy, and electrical conductivity. Below T V , a normal Fe 3ϩ high-spin state in a symmetrical square-pyramidal coordination appears, whereas Fe 2ϩ is distorted. The long-range order of this arrangement is solved from high-resolution powder neutron diffraction data. Rietveld refinements show that the charge-ordered spins have AFM interactions in all three directions (G type͒ whereas in the mixed-valence state a ferromagnetic ͑FM͒ interaction appears between the iron atoms facing each other across the Tb layer. This FM interaction is suggested to be essential for the appearance of the mixed-valence state via the double-exchange sharing of the Fe 2ϩ -originated electron. This also allows for the total ordered spin moment being unchanged at the Verwey transition, following one single Brillouin curve. Analogous cases are pointed out where the Verwey transition proceeds in a similar manner, also at the molecular level.

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Section: Mössbauer Studiessupporting

confidence: 67%

Verwey transition in mixed-valenceTbBaFe2O5: Two attempts to order charges

et al. 2001

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Preparation and characterization of powders and crystals of V_n‐xTi_xO_2n‐1 Magneli oxides

Calestani¹,

Licci

Kopnin

et al. 2005

Cryst. Res. Technol.

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V n-x Ti x O 2n-1 Magnéli phases have been synthesized under vacuum in powder form (n=4, 0≤x≤0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl 4 and NH 4 Cl were used as transporting agents. Needle-shaped crystals as long as 200-300 micrometers or 2-3 mm were obtained when in presence of NH 4 Cl or TeCl 4 , respectively. The powder and crystal structures were examined by X-ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single-phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X-ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Végard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P-1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four-points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V 4 O 7 . The metal-insulator transitions observed in V 4 O 7 and V 5 O 9 , at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides.

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Density-functional calculations of the crystal structures and properties ofCsCr3O8andA
Vidya
¹
,
Kjekshus
²
,
Fjellvåg
³

2006
Phys. Rev. B
3
0
3
0
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X-Ray powder diffraction study of the phase transitions in Ti₄O₇

Cited by 3 publications

References 16 publications

Verwey transition in mixed-valenceTbBaFe2O5: Two attempts to order charges

Verwey transition in mixed-valenceTbBaFe2O5: Two attempts to order charges

Preparation and characterization of powders and crystals of V_n‐xTi_xO_2n‐1 Magneli oxides

Density-functional calculations of the crystal structures and properties ofCsCr3O8andA
Vidya
¹
,
Kjekshus
²
,
Fjellvåg
³

2006
Phys. Rev. B
3
0
3
0
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X-Ray powder diffraction study of the phase transitions in Ti4O7

Cited by 3 publications

References 16 publications

Verwey transition in mixed-valenceTbBaFe2O5: Two attempts to order charges

Verwey transition in mixed-valenceTbBaFe2O5: Two attempts to order charges

Preparation and characterization of powders and crystals of Vn‐xTixO2n‐1 Magneli oxides

Density-functional calculations of the crystal structures and properties ofCsCr3O8andAVidya1, Kjekshus2, Fjellvåg3 2006Phys. Rev. B3030View full textAdd to dashboardCite

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About

X-Ray powder diffraction study of the phase transitions in Ti₄O₇

Preparation and characterization of powders and crystals of V_n‐xTi_xO_2n‐1 Magneli oxides

Density-functional calculations of the crystal structures and properties ofCsCr3O8andA
Vidya
¹
,
Kjekshus
²
,
Fjellvåg
³

2006
Phys. Rev. B
3
0
3
0
View full text Add to dashboard Cite