Synthesis, crystal chemistry, and electrical properties of the intergrowth oxides Sr{sub 4{minus}x}Ca{sub x}Fe{sub 6{minus}y}Co{sub y}O{sub 13+{delta}}

Journal Article · Tue Jun 01 00:00:00 EDT 1999 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1999.8261· OSTI ID:679233

Guggilla, S; Armstrong, T; Manthiram, A ^[1]

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1. Univ. of Texas, Austin, TX (United States). Texas Materials Inst.

Sr{sub 4{minus}x}Ca{sub x}Fe{sub 6{minus}y}Co{sub y}O{sub 13+{delta}} oxides crystallizing in an orthorhombic intergrowth structure in which perovskite-type SrO-(Fe, Co)O{sub 2}-SrO layers alternate with (Fe, Co){sub 2}O{sub 2.5} layers along the b axis have been synthesized. The Ca solubility decreases from x = 3.2 at y = 0 to x = 1.6 at y = 1.8. The cell parameters and volume decrease monotonically with increasing Ca content. While the unsubstituted Sr{sub 4}Fe{sub 6}O{sub 13+{delta}} has {delta} {approx} 0.4 excess oxygen, the substitution of Ca and Co tends to decrease the oxygen content and average oxidation state toward, respectively, 13.0 and 3.0+. The total conductivity of Sr{sub 4{minus}x}Ca{sub x}Fe{sub 6{minus}y}Co{sub y}O{sub 13+{delta}} (0 {le} y {le} 0.6) increases with increasing Ca content x, which is in contrast to that found in the perovskite system Sr{sub 1{minus}x}Ca{sub x}FeO{sub 3{minus}{delta}}. The conductivity versus temperature plots of Sr{sub 4{minus}x}Ca{sub x}Fe{sub 6}O{sub 13+{delta}} exhibit a change in the sign of the slope from positive to negative at around 450 C for x {ge} 1.6. While a similar transition in the perovskite system SrFeO{sub 3{minus}{delta}} is related to oxygen loss, no oxygen loss is observed up to at least 900 C in Sr{sub 4{minus}x}Ca{sub x}Fe{sub 6}O{sub 13+{delta}}. High-temperature X-ray diffraction does not reveal any structural changes up to 750 C and high values of thermoelectric power rule out the possibility of metallic behavior at T > 450 C. The observed transition is attributed to a possible redistribution of the charge carriers between the perovskite and nonperovskite layers at T > 450 C. 20 refs., 14 figs.

• Sponsoring Organization: Petroleum Research Fund (United States); Welch (Robert A.) Foundation, Houston, TX (United States)
• OSTI ID: 679233
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 145; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CALCIUM OXIDES
COBALT OXIDES
CRYSTAL STRUCTURE
ELECTRIC CONDUCTIVITY
EXPERIMENTAL DATA
IRON OXIDES
STRONTIUM OXIDES
SYNTHESIS
TEMPERATURE DEPENDENCE
X-RAY DIFFRACTION