Anomalous thermoelectric power in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi><mml:mi mathvariant="normal">Fe</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>from charge ordering and phase separation

Hemery, E. K.; Williams, G. V. M.; Trodahl, H. J.

doi:10.1103/physrevb.75.092403

Cited by 30 publications

(19 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The sintering and annealing processes are described elsewhere. 7 The oxygen contents were estimated by first noting that the temperature-dependent magnetization of the as-made sample corresponds to published data for x = 2.95. The samples were then annealed at different temperatures and oxygen partial pressures or in pure argon and then rapidly quenched into liquid nitrogen.…”

Section: Methodsmentioning

confidence: 99%

“…1,2 There is also a large jump in the thermopower near this temperature that has been interpreted in terms of charge ordering on one of the Fe sites. 7 Decreasing the oxygen content below 2.875 leads to the orthorhombic Sr 4 Fe 4 O 11 ͑x = 2.75͒ phase ͓Fig. 1͑b͔͒ that contains square pyramidal Fe͑1͒O 5 and distorted Fe͑2͒O 6 octahedra.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Magnetic and transport properties ofSrFeOx

2009

Self Cite

View full text Add to dashboard Cite

We report the results from magnetic and transport measurements on SrFeO x where we focus on oxygen contents about the Sr 4 Fe 4 O 11 phase ͑x = 2.75͒ that antiferromagnetically orders at ϳ230 K. We find an exchange-bias-like effect in Sr 4 Fe 4 O 11 that commences near the Fe͑2͒ moment Néel temperature ͑ϳ230 K͒. While there is a weak spin-glass component, possibly arising from spin-frustrated moments on the Fe͑1͒ sites, the spin-glass temperature is significantly less than 230 K, and hence the exchange-bias-like effect is unlikely to be due to a spin glass. The exchange-bias-like effect clearly arises from an exchange interaction term that includes the Fe͑2͒ spins but its exact nature is not clear and awaits a detailed theoretical study. Roomtemperature thermopower measurements show a large change in sign for oxygen contents on either side of the Sr 4 Fe 4 O 11 phase, which we show can be qualitatively interpreted by assuming that the Fermi level is within a narrow band. High-field resistivity measurements show a large magnetoresistance that commences near the Sr 4 Fe 4 O 11 Néel temperature.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnetic and transport properties ofSrFeOx

2009

Self Cite

View full text Add to dashboard Cite

show abstract

“…Thus, as shown in Figure 4d, we measured the thermopower of SCO thin films at 300 K. Note that the thermoelectric measurement is particularly sensitive to the change in the carrier concentration from hole doping and/or variation in oxygen content. [30][31][32] First, a systematic decrease in the thermopower was observed upon increase of oxygen content or hole doping in SCO thin films.…”

Section: Changes In the Magnetic Properties By Valence State Modificamentioning

confidence: 99%

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

et al. 2013

View full text Add to dashboard Cite

Oxygen stoichiometry is one of the most important elements in determining the physical properties of transition metal oxides (TMOs). A small change in the oxygen content results in the variation of valence state of the transition metal, drastically modifying the materials functionalities. The latter includes, for instance, (super-)conductivity, magnetism, ferroelectricity, bulk ionic conduction, and catalytic surface reactions. [1][2][3][4][5] In particular, among those applications, TMOs with mixed valence states have attracted attention for many environmental and renewable energy applications, including catalysts, hydrogen generation from water splitting, cathodes in rechargeable batteries and solid oxide fuel cells, and oxygen separation membranes. [6][7][8] For example, previous studies have shown that the ability to control the number of d-band electron population and detailed spin configuration in TMOs is critical for improved catalytic performance of TMOs. [9,10] In this context, SrCoO x (2.5 ≤ x ≤ 3.0) is an ideal class of materials to study the evolution of the physical properties by modifying the valence state in TMOs, due to the existence of two structurally distinct topotactic phases, i.e. the brownmillerite SrCoO 2.5 (BM-2 SCO) (see Figure 1a) and the perovskite SrCoO 3 . [11,12] Especially, BM-SCO has atomicallyordered one-dimensional vacancy channels (see Figure 1a), which can accommodate additional oxygen when the valence state of Co is changed. Moreover, SrCoO x exhibits a wide spectrum of physical properties from antiferromagnetic insulator to ferromagnetic metal depending on the oxygen stoichiometry. [11][12][13] Since SrCoO x has only a single control knob, i.e. the oxygen contentx, to modify the Co valence state without cation doping, it is straightforward to study the valence state (i.e. oxygen content) dependent physical properties. However, so far, the growth of high quality single crystalline materials has not been as successful due to difficulty in controlling the right oxidation state.In this work, we report on the epitaxial growth of high quality BM-SCO single crystalline films on SrTiO 3 (STO) substrates by pulsed laser epitaxy (PLE). In order to examine the topotactic phase transformation to the perovskite SrCoO 3- (P-SCO), some of the samples were subsequently in-situ annealed at various oxygen pressure (P(O 2 )) to fill the oxygen vacancies.While the direct growth of P-SCO films with x = 3.0 was an arduous task, we found that postannealing in high P(O 2 ) (> several hundreds of Torr) could fill sufficient amount of oxygen vacancies, yielding systematic evolution in electronic, magnetic, and thermoelectric properties. (Figure 1b) demonstrate that the films are of high quality. X-ray rocking curve ω-scans revealed a full width half maximum (FWHM) of < 0.04º, demonstrating the excellent crystallinity (cf., FWHM of the 002 STO peak was ~0.02º) of our films (data not shown).While we have shown the XRD data from a well-optimized, high quality thin film, it is worthwhile to mention tha...

show abstract

“…In the n = 8 member SrFeO 2.875 , with nominal Fe 3.75+ , the oxygen vacancies order at 523 K and the ordering stabilizes the charge-ordered tetragonal phase with Fe 4+ O 6 octahedra, distorted Fe 3.5+ O 6 octahedra, and Fe 4+ O 5 pyramids1116. The tetragonal phase undergoes another phase transition at ~70 K, which is due to charge disproportionation of Fe 3.5+ into Fe 4+ and Fe 3+ and which is accompanied by an abrupt increase in the electrical resistivity14273031. Further increase in the oxygen vacancy concentration leads to SrFeO 2.75 ( n = 4) with nominal Fe 3.5+ 111632 and SrFeO 2.5 ( n = 2) with nominal Fe 3+ 1617333435363738.…”

mentioning

confidence: 99%

Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

Hirai

Kan

Ichikawa

et al. 2015

Sci Rep

View full text Add to dashboard Cite

Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.

show abstract

Anomalous thermoelectric power inSrFeO3−δfrom charge ordering and phase separation

Cited by 30 publications

References 21 publications

Magnetic and transport properties ofSrFeOx

Magnetic and transport properties ofSrFeOx

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

Contact Info

Product

Resources

About

Anomalous thermoelectric power inSrFeO3−δfrom charge ordering and phase separation

Cited by 30 publications

References 21 publications

Magnetic and transport properties ofSrFeOx

Magnetic and transport properties ofSrFeOx

Topotactic Phase Transformation of the Brownmillerite SrCoO2.5 to the Perovskite SrCoO3–δ

Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

Contact Info

Product

Resources

About

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ