Brownmillerite Ca2Co2O5: Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal Structural Transitions

Zhang, Junjie; Zheng, Hong; Malliakas, Christos D.; Allred, Jared M.; Ren, Yang; Li, Qingan; Han, Tianheng; Mitchell, J. F.

doi:10.1021/cm503873x

Cited by 37 publications

(18 citation statements)

References 59 publications

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“…The thermoelectric Ca 3 Co 4 O 9 phase could not be detected in neither the 2ST sintered Fe and Ni added samples, where the main phases have been found to be Ca 3 Co 2 O 6 and brownmillerite Ca 2 (Co,Fe) 2 O 5 [ 67 ], for the Fe additions, and Ca 3 Co 2 O 6 and (Co,Ni)O, for the samples with Ni additions. Some minor reflections corresponding to the Ca 3 Co 4 O 9 phase are slightly visible in Figure 7 , only for the 3Ni_2ST samples.…”

Section: Resultsmentioning

confidence: 99%

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

et al. 2021

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This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components, encouraged by our recent promising results obtained for similar cobalt additions. Iron and nickel were chosen because of their similarities with cobalt. The maximum power factor value of around 200 μWm−1K−2 at 925 K was achieved for the composite with the nominal nickel content of 3% vol., processed via the two-step sintering cycle, which provides the highest densification from this work. The effectiveness of the proposed approach was shown to be strongly dependent on the processing conditions and added amounts of metallic particles. Although the conventional one-step approach results in Fe- and Ni-containing composites with the major content of the thermoelectric Ca3Co4O9 phase, their electrical performance was found to be significantly lower than for the Co-containing analogue, due to the presence of less-conducting phases and excessive porosity. In contrast, the relatively high performance of the composite with a nominal nickel content of 3% vol. processed via a two-step approach is related to the specific microstructural features from this sample, including minimal porosity and the presence of the Ca2Co2O5 phase, which partially compensate the complete decomposition of the Ca3Co4O9 matrix. The obtained results demonstrate different pathways to tailor the phase composition of Ca3Co4O9-based materials, with a corresponding impact on the thermoelectric performance, and highlight the necessity of more controllable approaches for the phase composition tuning, including lower amounts and different morphologies of the dispersed metallic phases.

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Section: Resultsmentioning

confidence: 99%

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

et al. 2021

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“…7 Ordered tilts of the tetrahedra can give rise to low symmetry superstructures, 13 as found in other reported Ca 2 M 2 O 5 brownmillerites at room temperature. Ca 2 Fe 2 O 5 has a Pnma superstructure 14 17 Fits of the two simple ordering models to the 300 K profile of Ca 2 Cr 2 O 5 gave a slightly better goodness-of-fit χ 2 = 1.63 for I2mb than for Pnma where χ 2 = 1.69, and no breaking of the body-centring reflection condition was observed. Hence the I2mb model is reported here as the ordered brownmillerite superstructure for Ca 2 Cr 2 O 5 between 10 and 300 K, and this symmetry is corroborated by the analysis of structural parameters described below.…”

Section: Crystal Structurementioning

confidence: 96%

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

Arévalo‐López

Attfield

2015

Dalton Trans.

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Powder neutron diffraction and magnetic susceptibility measurements at 10-300 K have been used to determine the crystal and magnetic structures of brownmillerite type Ca(2)Cr(2)O(5), which was obtained by reduction of the high pressure phase CaCrO(3) through hard-soft chemistry. The ambient temperature crystal structure of Ca(2)Cr(2)O(5) is refined in space group I2mb and the unusual tetrahedral coordination of Cr(3+) results in local structural distortions. Cr(3+) spins order antiferromagnetically below 220 K and a substantial observed canting of moments shows that Heisenberg exchange is weak or frustrated and competes with antisymmetric Dzialoshinskii-Moriya interactions.

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“…The three different ordering schemes shown in Figure 2 better maximize either factor (i ) or (ii ), at the expense of the other. Following the approach of Zhang et al, 39 we can assign a magnitude to the local dipole generated by the tetrahedral rotations (P T , Table I, given in units of Debye). P T is calculated based on the Debye equation, µ = neR, where µ is the net dipole moment, n is the number of electrons, e is the elementary charge, and R is the distance between centers of charge; following the approach of Poeppelmeier et al, we estimated the distribution of electrons using bond valence sums.…”

Section: A Polyhedral Rotation Definitionsmentioning

confidence: 99%

Crystal structure and electronic properties of bulk and thin film brownmillerite oxides

Young¹,

Rondinelli²

2015

Phys. Rev. B

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The equilibrium structure and functional properties exhibited by brownmillerite oxides, a family of perovskite-derived structures with alternating layers of BO6 octahedra and BO4 tetrahedra, viz., ordered arrangements of oxygen vacancies, is dependent on a variety of competing crystal-chemistry factors. We use electronic structure calculations to disentangle the complex interactions in two ferrates, Sr2Fe2O5 and Ca2Fe2O5, relating the stability of the equilibrium (strain-free) and thin film structures to both previously identified and newly herein proposed descriptors. We show that cation size and intralayer separation of the tetrahedral chains provide key contributions to the preferred ground state. We show the bulk ground state structure is retained in the ferrates over a range of strain values; however, a change in the orientation of the tetrahedral chains, i.e., a perpendicular orientation of the vacancies relative to the substrate, is stabilized in the compressive region. The structure stability under strain is largely governed by maximizing the intraplane separation of the 'dipoles' generated from rotations of the FeO4 tetrahedra. Lastly, we find that the electronic band gap is strongly influenced by strain, manifesting as an unanticipated asymmetric-vacancy alignment dependent response. This atomistic understanding establishes a practical route for the design of functional electronic materials in thin film geometries.

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Brownmillerite Ca₂Co₂O₅: Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal Structural Transitions

Abstract: Ca 2 Co 2 O 5 in the brownmillerite form was synthesized using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4×0.8×0.5 mm 3 were obtained.

Cited by 37 publications

References 59 publications

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

Crystal structure and electronic properties of bulk and thin film brownmillerite oxides

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Brownmillerite Ca2Co2O5: Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal Structural Transitions

Abstract: Ca 2 Co 2 O 5 in the brownmillerite form was synthesized using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4×0.8×0.5 mm 3 were obtained.

Cited by 37 publications

References 59 publications

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

Crystal and magnetic structures of the brownmillerite Ca2Cr2O5

Crystal structure and electronic properties of bulk and thin film brownmillerite oxides

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Product

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Brownmillerite Ca₂Co₂O₅: Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal Structural Transitions

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅