Structural behavior and thermoelectric properties of the brownmillerite system Ca{sub 2}(Zn{sub x}Fe{sub 2-x})O{sub 5}

Journal Article · Mon Aug 15 04:00:00 EDT 2011 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2011.06.009· OSTI ID:21580199

Asenath-Smith, Emily ^[1]; Misture, Scott T; Edwards, Doreen D ^[1]

---

1. Alfred University, Kazuo Inamori School of Engineering, Materials Science and Engineering, 2 Pine Street, Alfred, NY 14802 (United States)

The Ca{sub 2}(Zn{sub x}Fe{sub 2-x})O{sub 5} series was synthesized and characterized to determine the influence of zinc dopant on the brownmillerite structure for thermoelectric applications. All single-phase compounds exhibited Pnma symmetry at room temperature up to the solubility limit at x=0.10. High-temperature X-ray powder diffraction was used to show that the nature of the Pnma-Imma(0 0 {gamma})s00 transition in Ca{sub 2}Fe{sub 2}O{sub 5} is modified by the presence of zinc. While the Zn-free composition transitions to an incommensurate phase, the Zn-containing phases transition instead to a commensurate phase, Imma(0 0 {gamma})s00 with {gamma}=1/2. Both the Neel temperature and the onset temperature of the Pnma-Imma(0 0 {gamma})s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 deg. C demonstrates that the structure contains statistically disordered chain orientations as described by space group Imma. Thermoelectric properties were analyzed in air from 100 to 800 deg. C. The positive Seebeck coefficient revealed hole-type conduction for all compositions. Doped samples exhibited electrical conductivities up to 3.4 S/cm and thermal conductivity of 1.5 W/mK. Transport analysis revealed thermally activated mobility consistent with polaron conduction behavior for all compositions. - Graphical Abstract: Preferential substitution by zinc for iron at the tetrahedral sites of brownmillerite dicalcium ferrite modifies the high temperature Imma(0 0 {gamma})s00 phase from incommensurate to commensurate. Highlights: > Preferential tetrahedral occupancy by zinc in brownmillerite dicalcium ferrite. > Ca{sub 2}Fe{sub 2}O{sub 5} exhibits two additional phase transitions above 1000 deg. C: a commensurately modulated Imma(0 0 {gamma})s00 phase and a statistically disordered Imma phase. > Thermal hysteresis in phase transition increased with increasing zinc. > Electrical conductivity up to 3.4 S/cm at 800 deg. C.

• OSTI ID: 21580199
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 8 Vol. 184; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ALLOYS
CARBON ADDITIONS
CHEMICAL ANALYSIS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
FERRIMAGNETIC MATERIALS
FERRITE
FERRITES
ION MICROPROBE ANALYSIS
IRON ALLOYS
IRON COMPOUNDS
MAGNETIC MATERIALS
MATERIALS
METALS
MICROANALYSIS
NEEL TEMPERATURE
NONDESTRUCTIVE ANALYSIS
ORTHORHOMBIC LATTICES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SCATTERING
SPACE GROUPS
SYMMETRY GROUPS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TETRAGONAL LATTICES
THERMAL CONDUCTIVITY
THERMODYNAMIC PROPERTIES
THERMOELECTRIC PROPERTIES
TRANSITION ELEMENT ALLOYS
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE
X-RAY DIFFRACTION
ZINC