Doreen Edwards | Alfred University (original) (raw)

Papers by Doreen Edwards

Cheminform, 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Applied Physics Letters, 1997

A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, h... more A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, has been identified. The equilibrium phase relationships of this new material with respect to three other TCOs in Ga2O3–In2O3–SnO2 are reported. The optical properties of this phase are slightly superior to Sn-doped indium oxide (ITO) and depend on composition. A room-temperature conductivity of 375 Ω cm−1 was obtained for H2-reduced Ga2.4In5.6Sn2O16. This value is an order of magnitude lower than commercial ITO films, but comparable to values reported for bulk, polycrystalline Sn-doped In2O3.

Journal of The American Ceramic Society, 1997

Journal of Solid State Chemistry, 2008

Over 100 samples were prepared as (Ga,In)4(Sn,Ti)n−4O2n−2, n=6, 7, and 9 by solid-state reaction ... more Over 100 samples were prepared as (Ga,In)4(Sn,Ti)n−4O2n−2, n=6, 7, and 9 by solid-state reaction at 1400 °C and characterized by X-ray diffraction. Nominally phase-pure beta-gallia–rutile intergrowths were observed in samples prepared with n=9 (0.17⩽x⩽0.35 and 0⩽y⩽0.4) as well as in a few samples prepared with n=6 and 7. Rietveld analysis of neutron time-of-flight powder diffraction data were conducted for three phase-pure samples. The n=6 phase Ga3.24In0.76Sn1.6Ti0.4O10 is monoclinic, P2/m, with Z=2 and a=11.5934(3) Å, b=3.12529(9) Å, c=10.6549(3) Å, β=99.146(1)°. The n=7 phase Ga3.24In0.76Sn2.4Ti0.6O12 is monoclinic, C2/m, with Z=2 and a=14.2644(1) Å, b=3.12751(2) Å, c=10.6251(8) Å, β=108.405(1)°. The n=9 phase Ga3.16In0.84Sn4TiO16 is monoclinic, C2/m, with Z=2 a=18.1754(2) Å, b=3.13388(3) Å, c=10.60671(9) Å, β=102.657(1)°. All of the structures are similar in that they possess distorted hexagonal tunnels parallel to the [010] vector.The structures of three beta-gallia–rutile intergrowths, expressed as (Ga,In)4(Sn,Ti)n−4O2n−2, n=6, 7, and 9, were refined using Rietveld analysis of neutron time-of-flight powder diffraction data. The n=6 phase Ga3.24In0.76Sn1.6Ti0.4O10 crystallizes in P2/m whereas the n=7 and 9 phases crystallize in C2/m. All structure are similar in that they possess hexagonal tunnels parallel to the [010] vector.

Applied Physics Letters, 1997

A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, h... more A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, has been identified. The equilibrium phase relationships of this new material with respect to three other TCOs in Ga2O3–In2O3–SnO2 are reported. The optical properties of this phase are slightly superior to Sn-doped indium oxide (ITO) and depend on composition. A room-temperature conductivity of 375 Ω cm−1 was obtained for H2-reduced Ga2.4In5.6Sn2O16. This value is an order of magnitude lower than commercial ITO films, but comparable to values reported for bulk, polycrystalline Sn-doped In2O3.

Solid State Ionics, 2007

The Aurivillius ceramics Bi(2−y)PbySr2Nb2TiO(12−δ) and Bi2Sr2Nb2Ti(1−x)MxO(12−δ) (M = Fe, Cr, Mn)... more The Aurivillius ceramics Bi(2−y)PbySr2Nb2TiO(12−δ) and Bi2Sr2Nb2Ti(1−x)MxO(12−δ) (M = Fe, Cr, Mn) were successfully prepared and the solid solubility limits were determined to be y = 0.2 and x = 0.2. The solubility limits for the phases are limited by the oxygen vacancy concentration. The electrical conductivity was measured as a function of temperature and oxygen activity, and showed that undoped Bi2Sr2Nb2TiO12 is an electronic conductor at high oxygen activity, while acceptor doping with Pb or Fe results in ionic conduction. The total conductivity increases with dopant concentration to a maximum at the solubility limits of 7.5 × 10− 4 to 10 × 10− 4 S/cm at 800 °C for Pb, Fe, and Mn dopants.

Journal of Solid State Chemistry, 2000

The structures of several Ga2O3–In2O3–SnO2 phases were investigated using high-resolution electro... more The structures of several Ga2O3–In2O3–SnO2 phases were investigated using high-resolution electron microscopy, X-ray diffraction, and Rietveld analysis of time-of-flight neutron diffraction data. The phases, expressed as Ga4−4xIn4xSnn−4O2n−2 (n=6 and 7–17, odd), are intergrowths between the β-gallia structure of (Ga,In)2O3 and the rutile structure of SnO2. Samples prepared with n≥9 crystallize in C2/m and are isostructural with intergrowths in the Ga2O3–TiO2 system. Samples prepared with n=6 and n=7 are members of an alternative intergrowth series that crystallizes in P2/m. Both intergrowth series are similar in that their members possess 1-D tunnels along the b axis. The difference between the two series is described in terms of different crystallographic shear plane operations (CSP) on the parent rutile structure.

Journal of Solid State Chemistry, 1998

Direct methods using dynamical transmission electron diffraction (TED) intensities is applied to ... more Direct methods using dynamical transmission electron diffraction (TED) intensities is applied to the solution of (Ga,In)2SnO5. Dynamical diffraction effects in the TED data lead to an emphasis of oxygen positions in the structure. Application of direct methods to dynamical diffraction intensities represents a valuable new technique for obtaining approximate atom positions of light elements in ceramics using an experiment which is simple to perform and does not require a single crystal.

Solid State Ionics, 1997

Overlooked apparatus (cabling, leads, sample holder) contributions to experimental impedance spec... more Overlooked apparatus (cabling, leads, sample holder) contributions to experimental impedance spectra can be significant, especially at high frequencies, and can obscure the true sample response. Instrumental limitations are discussed and high-frequency artifacts arising from apparatus contributions are investigated as they pertain to accurate impedance measurements of materials systems. Remediation strategies are presented, including geometrical adjustments, lead shielding, and null-correction procedures.

Solid State Ionics, 2000

In-based transparent conducting oxides (TCOs) share the prevailing defect structure of indium–tin... more In-based transparent conducting oxides (TCOs) share the prevailing defect structure of indium–tin oxide (ITO), i.e. electrons, isolated SnIn⋅ donors, and neutral associates, believed to be (2SnIn⋅Oi″)x. The present work reviews the state of the literature, presents calculated Brouwer diagrams vs. oxygen partial pressure and vs. dopant concentration, and reports intermediate temperature electrical property data (thermopower, conductivity) vs. pO2 and Sn concentration for three systems — polycrystalline bulk ITO, nanocrystalline ITO, and the recently reported ternary cation TCO, Ga3−xIn5+xSn2O16. The influence of non-reduceable tin–oxygen complexes at high doping levels is identified for ITO. Ramifications for In-based TCO properties are discussed.

Journal of Solid State Chemistry, 2011

... Highlights. ► XPS and DRIFT were measured on BSCF (BSCF: x=0–0.8) samples. ► The identity of ... more ... Highlights. ► XPS and DRIFT were measured on BSCF (BSCF: x=0–0.8) samples. ► The identity of Ba 3d /Co 2p XPS shoulder peak at 778.0 was suggested. ► The bonding behavior of CO 3 2− to the BSCF prevoskite structure was studied substantially. ...

Journal of Solid State Chemistry, 2011

The X-ray photoelectron spectra (XPS) of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1–xO3–δ,0≤x≤0.8) ... more The X-ray photoelectron spectra (XPS) of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1–xO3–δ,0≤x≤0.8) were measured at room temperature (RT). Peak areas of Fe2p1, Fe2p3, Fe3p and Co3p increased systematically with increasing cobalt concentration, while their binding energies (BEs) remained the same (723.3, 710.0, 55.0 and 60.9 eV, respectively). However, the BEs of lattice oxygen in O1s (528.1 eV) and Ba4d for the BaO bond (87.9V and 90.2 eV) increased with increasing cobalt concentration. The shoulder peak of Ba3d/Co2p increased from 778.0 to 778.7 eV, which implies that this peak can be attributed to another Ba XPS peak (described as Ba2nd in this study) due to the overlapping area between barium cations and oxygen anions. The overall peak areas of Ba4d increased up to x=0.4, and then decreased, which coincides with the behavior of the Diffuse Reflectance Infrared Fourier Transform (DRIFT) bands representing adsorbed CO32− (νCO32−) and structurally bonded CO32− (ν2, ν3) (800–1200 and 862/1433 cm−1, respectively).The bonding of CO32− to the surface of BSCF perovskite and the bonding state between cations vs. oxygen have been suggested.► XPS and DRIFT were measured on BSCF (BSCF: x=0–0.8) samples. ► The identity of Ba3d/Co2p XPS shoulder peak at ∼778.0 was suggested. ► The bonding behavior of CO32− to the BSCF prevoskite structure was studied substantially.

Journal of Materials Science, 2011

X-ray diffraction (XRD) and the X-ray photoelectron spectroscopy (XPS) were measured for the sint... more X-ray diffraction (XRD) and the X-ray photoelectron spectroscopy (XPS) were measured for the sintered BSCF ceramics (Ba 0.5 Sr 0.5 Co x Fe 1-x O 3-d , x = 0.2 and 0.8: BSCF5528 and BSCF5582, respectively), which were annealed at different temperatures (700 and 950°C) and gases (O 2 and Ar). The unit cell of the annealed BSCF5528 at 950°C under Ar expanded by 0.8%, while contracting by 0.45% under O 2 . The cubic and rhombohedral phases coexist in the BSCF5582 annealed at 700°C under O 2 . The XPS peak areas of lattice oxygen (O 2-) in O 1s , *528 eV, and the shoulder peak of Co 2p /Ba 3d in BSCF5582 (*778 eV) increased significantly after being annealed in O 2 . The areas of the peaks for BaCO 3 (87.9/ 90.2 eV) in Ba 4d preferentially were shown to decrease in Ar and increase in O 2 .

Metal Powder Report

The electrical conductivity and Seebeck coefficient of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1 −... more The electrical conductivity and Seebeck coefficient of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1 − xO3 − δ, 0 ≤ x ≤ 0.8) were simultaneously measured as a function of pO2 (10− 5 ≤ pO2 ≤ 1 atm) at 500 °C, 700 °C and 900 °C. All samples exhibited a positive Seebeck coefficient over the range of pO2 and temperature examined, which indicates the predominance of p-type conduction. In all cases, conductivity increased with increasing pO2, ranging from a minimum of ~ 0.6 S/cm (x = 0, pO2 = 10− 5 atm, T = 900 °C) to a maximum of ~ 36 S/cm (x = 0.8, pO2 = 1 atm, and T = 900 °C). At low temperatures and high pO2, conductivity was approximately proportional to pO21/4, which was attributed to the reduction of B-site cations from their tetravalent to trivalent state. At low pO2 and high temperature, the conductivity exhibited positive deviations from the pO21/4 dependence. At 500 °C and x ≤ 0.6, the Seebeck coefficient (Q) decreased linearly with increasing log pO2. At 700 and 900 °C, Q vs. log pO2 curves exhibited maxima at 10− 3 < pO2 < 10− 1 atm, and the maxima shifted to higher pO2 as x increased. A simple p-type polaron hopping model, assuming negligible contribution from n-type or ionic carriers, was used to extract the carrier concentration of the x = 0.8 sample from the measured thermopower data. The calculated hole mobility for the x = 0.8 sample was less than 0.1 cm2/V-s, confirming a p-type polaron-hopping model. This analysis, as well as analysis of Jonker plots, suggested that hole mobility decreased with decreasing pO2.► Conductivity and Seebeck coefficient of BSCF was measured. ► BSCF materials are p-type polaron conductors at 500 °C–900 °C and 10–5 < pO2 < 1 atm. ► Seebeck coefficient and oxygen non-stoichiometry used to calculate valence state of Bn+. ► Hole mobility decreases with decreasing pO2.

Journal of Solid State Chemistry, 2011

The Ca2(ZnxFe2−x)O5 series was synthesized and characterized to determine the influence of zinc d... more The Ca2(ZnxFe2−x)O5 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 γ)s00 transition in Ca2Fe2O5 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 γ)s00 with γ=1/2. Both the Néel temperature and the onset temperature of the Pnma–Imma(0 0 γ)s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 °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 °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.Preferential substitution by zinc for iron at the tetrahedral sites of brownmillerite dicalcium ferrite modifies the high temperature Imma(0 0 γ)s00 phase from incommensurate to commensurate.► Preferential tetrahedral occupancy by zinc in brownmillerite dicalcium ferrite. ► Ca2Fe2O5 exhibits two additional phase transitions above 1000°C: a commensurately modulated Imma(0 0 γ)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 °C.

Solar Energy Materials and Solar Cells, 2009

Composite porcelain-enamel coatings consisting of spinel-type transition-metal-oxide pigments emb... more Composite porcelain-enamel coatings consisting of spinel-type transition-metal-oxide pigments embedded in a borosilicate-glass matrix were deposited on 321 stainless steel using screen-printing techniques and characterized using total reflectance over the spectral range of 200 nm to 25 mm. The composite coatings exhibited moderate spectral selectivity and excellent thermal stability at 450 1C. Solar absorptance (a) ranged from 0.82 to 0.90 and calculated thermal emittance at 500 1C (e) ranged from 0.46 to 0.79. Both depended on coating thickness and pigment volume concentrations. As an example, the highest solar selectivity was measured in a 0.9 mm coating with a and e (500 1C) being 0.82 and 0.46, respectively.

Journal of Solid State Chemistry, 2010

Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (di... more Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion αL) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma–Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α2σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden–Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10−6 K−1) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers.Representative microstructure of Ca2Fe2O5 samples used for thermoelectrical measurements.

Cheminform, 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Applied Physics Letters, 1997

A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, h... more A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, has been identified. The equilibrium phase relationships of this new material with respect to three other TCOs in Ga2O3–In2O3–SnO2 are reported. The optical properties of this phase are slightly superior to Sn-doped indium oxide (ITO) and depend on composition. A room-temperature conductivity of 375 Ω cm−1 was obtained for H2-reduced Ga2.4In5.6Sn2O16. This value is an order of magnitude lower than commercial ITO films, but comparable to values reported for bulk, polycrystalline Sn-doped In2O3.

Journal of The American Ceramic Society, 1997

Journal of Solid State Chemistry, 2008

Over 100 samples were prepared as (Ga,In)4(Sn,Ti)n−4O2n−2, n=6, 7, and 9 by solid-state reaction ... more Over 100 samples were prepared as (Ga,In)4(Sn,Ti)n−4O2n−2, n=6, 7, and 9 by solid-state reaction at 1400 °C and characterized by X-ray diffraction. Nominally phase-pure beta-gallia–rutile intergrowths were observed in samples prepared with n=9 (0.17⩽x⩽0.35 and 0⩽y⩽0.4) as well as in a few samples prepared with n=6 and 7. Rietveld analysis of neutron time-of-flight powder diffraction data were conducted for three phase-pure samples. The n=6 phase Ga3.24In0.76Sn1.6Ti0.4O10 is monoclinic, P2/m, with Z=2 and a=11.5934(3) Å, b=3.12529(9) Å, c=10.6549(3) Å, β=99.146(1)°. The n=7 phase Ga3.24In0.76Sn2.4Ti0.6O12 is monoclinic, C2/m, with Z=2 and a=14.2644(1) Å, b=3.12751(2) Å, c=10.6251(8) Å, β=108.405(1)°. The n=9 phase Ga3.16In0.84Sn4TiO16 is monoclinic, C2/m, with Z=2 a=18.1754(2) Å, b=3.13388(3) Å, c=10.60671(9) Å, β=102.657(1)°. All of the structures are similar in that they possess distorted hexagonal tunnels parallel to the [010] vector.The structures of three beta-gallia–rutile intergrowths, expressed as (Ga,In)4(Sn,Ti)n−4O2n−2, n=6, 7, and 9, were refined using Rietveld analysis of neutron time-of-flight powder diffraction data. The n=6 phase Ga3.24In0.76Sn1.6Ti0.4O10 crystallizes in P2/m whereas the n=7 and 9 phases crystallize in C2/m. All structure are similar in that they possess hexagonal tunnels parallel to the [010] vector.

Applied Physics Letters, 1997

A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, h... more A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16;0.2⩽x⩽1.6, has been identified. The equilibrium phase relationships of this new material with respect to three other TCOs in Ga2O3–In2O3–SnO2 are reported. The optical properties of this phase are slightly superior to Sn-doped indium oxide (ITO) and depend on composition. A room-temperature conductivity of 375 Ω cm−1 was obtained for H2-reduced Ga2.4In5.6Sn2O16. This value is an order of magnitude lower than commercial ITO films, but comparable to values reported for bulk, polycrystalline Sn-doped In2O3.

Solid State Ionics, 2007

The Aurivillius ceramics Bi(2−y)PbySr2Nb2TiO(12−δ) and Bi2Sr2Nb2Ti(1−x)MxO(12−δ) (M = Fe, Cr, Mn)... more The Aurivillius ceramics Bi(2−y)PbySr2Nb2TiO(12−δ) and Bi2Sr2Nb2Ti(1−x)MxO(12−δ) (M = Fe, Cr, Mn) were successfully prepared and the solid solubility limits were determined to be y = 0.2 and x = 0.2. The solubility limits for the phases are limited by the oxygen vacancy concentration. The electrical conductivity was measured as a function of temperature and oxygen activity, and showed that undoped Bi2Sr2Nb2TiO12 is an electronic conductor at high oxygen activity, while acceptor doping with Pb or Fe results in ionic conduction. The total conductivity increases with dopant concentration to a maximum at the solubility limits of 7.5 × 10− 4 to 10 × 10− 4 S/cm at 800 °C for Pb, Fe, and Mn dopants.

Journal of Solid State Chemistry, 2000

The structures of several Ga2O3–In2O3–SnO2 phases were investigated using high-resolution electro... more The structures of several Ga2O3–In2O3–SnO2 phases were investigated using high-resolution electron microscopy, X-ray diffraction, and Rietveld analysis of time-of-flight neutron diffraction data. The phases, expressed as Ga4−4xIn4xSnn−4O2n−2 (n=6 and 7–17, odd), are intergrowths between the β-gallia structure of (Ga,In)2O3 and the rutile structure of SnO2. Samples prepared with n≥9 crystallize in C2/m and are isostructural with intergrowths in the Ga2O3–TiO2 system. Samples prepared with n=6 and n=7 are members of an alternative intergrowth series that crystallizes in P2/m. Both intergrowth series are similar in that their members possess 1-D tunnels along the b axis. The difference between the two series is described in terms of different crystallographic shear plane operations (CSP) on the parent rutile structure.

Journal of Solid State Chemistry, 1998

Direct methods using dynamical transmission electron diffraction (TED) intensities is applied to ... more Direct methods using dynamical transmission electron diffraction (TED) intensities is applied to the solution of (Ga,In)2SnO5. Dynamical diffraction effects in the TED data lead to an emphasis of oxygen positions in the structure. Application of direct methods to dynamical diffraction intensities represents a valuable new technique for obtaining approximate atom positions of light elements in ceramics using an experiment which is simple to perform and does not require a single crystal.

Solid State Ionics, 1997

Overlooked apparatus (cabling, leads, sample holder) contributions to experimental impedance spec... more Overlooked apparatus (cabling, leads, sample holder) contributions to experimental impedance spectra can be significant, especially at high frequencies, and can obscure the true sample response. Instrumental limitations are discussed and high-frequency artifacts arising from apparatus contributions are investigated as they pertain to accurate impedance measurements of materials systems. Remediation strategies are presented, including geometrical adjustments, lead shielding, and null-correction procedures.

Solid State Ionics, 2000

In-based transparent conducting oxides (TCOs) share the prevailing defect structure of indium–tin... more In-based transparent conducting oxides (TCOs) share the prevailing defect structure of indium–tin oxide (ITO), i.e. electrons, isolated SnIn⋅ donors, and neutral associates, believed to be (2SnIn⋅Oi″)x. The present work reviews the state of the literature, presents calculated Brouwer diagrams vs. oxygen partial pressure and vs. dopant concentration, and reports intermediate temperature electrical property data (thermopower, conductivity) vs. pO2 and Sn concentration for three systems — polycrystalline bulk ITO, nanocrystalline ITO, and the recently reported ternary cation TCO, Ga3−xIn5+xSn2O16. The influence of non-reduceable tin–oxygen complexes at high doping levels is identified for ITO. Ramifications for In-based TCO properties are discussed.

Journal of Solid State Chemistry, 2011

... Highlights. ► XPS and DRIFT were measured on BSCF (BSCF: x=0–0.8) samples. ► The identity of ... more ... Highlights. ► XPS and DRIFT were measured on BSCF (BSCF: x=0–0.8) samples. ► The identity of Ba 3d /Co 2p XPS shoulder peak at 778.0 was suggested. ► The bonding behavior of CO 3 2− to the BSCF prevoskite structure was studied substantially. ...

Journal of Solid State Chemistry, 2011

The X-ray photoelectron spectra (XPS) of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1–xO3–δ,0≤x≤0.8) ... more The X-ray photoelectron spectra (XPS) of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1–xO3–δ,0≤x≤0.8) were measured at room temperature (RT). Peak areas of Fe2p1, Fe2p3, Fe3p and Co3p increased systematically with increasing cobalt concentration, while their binding energies (BEs) remained the same (723.3, 710.0, 55.0 and 60.9 eV, respectively). However, the BEs of lattice oxygen in O1s (528.1 eV) and Ba4d for the BaO bond (87.9V and 90.2 eV) increased with increasing cobalt concentration. The shoulder peak of Ba3d/Co2p increased from 778.0 to 778.7 eV, which implies that this peak can be attributed to another Ba XPS peak (described as Ba2nd in this study) due to the overlapping area between barium cations and oxygen anions. The overall peak areas of Ba4d increased up to x=0.4, and then decreased, which coincides with the behavior of the Diffuse Reflectance Infrared Fourier Transform (DRIFT) bands representing adsorbed CO32− (νCO32−) and structurally bonded CO32− (ν2, ν3) (800–1200 and 862/1433 cm−1, respectively).The bonding of CO32− to the surface of BSCF perovskite and the bonding state between cations vs. oxygen have been suggested.► XPS and DRIFT were measured on BSCF (BSCF: x=0–0.8) samples. ► The identity of Ba3d/Co2p XPS shoulder peak at ∼778.0 was suggested. ► The bonding behavior of CO32− to the BSCF prevoskite structure was studied substantially.

Journal of Materials Science, 2011

X-ray diffraction (XRD) and the X-ray photoelectron spectroscopy (XPS) were measured for the sint... more X-ray diffraction (XRD) and the X-ray photoelectron spectroscopy (XPS) were measured for the sintered BSCF ceramics (Ba 0.5 Sr 0.5 Co x Fe 1-x O 3-d , x = 0.2 and 0.8: BSCF5528 and BSCF5582, respectively), which were annealed at different temperatures (700 and 950°C) and gases (O 2 and Ar). The unit cell of the annealed BSCF5528 at 950°C under Ar expanded by 0.8%, while contracting by 0.45% under O 2 . The cubic and rhombohedral phases coexist in the BSCF5582 annealed at 700°C under O 2 . The XPS peak areas of lattice oxygen (O 2-) in O 1s , *528 eV, and the shoulder peak of Co 2p /Ba 3d in BSCF5582 (*778 eV) increased significantly after being annealed in O 2 . The areas of the peaks for BaCO 3 (87.9/ 90.2 eV) in Ba 4d preferentially were shown to decrease in Ar and increase in O 2 .

Metal Powder Report

The electrical conductivity and Seebeck coefficient of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1 −... more The electrical conductivity and Seebeck coefficient of sintered BSCF ceramics (Ba0.5Sr0.5CoxFe1 − xO3 − δ, 0 ≤ x ≤ 0.8) were simultaneously measured as a function of pO2 (10− 5 ≤ pO2 ≤ 1 atm) at 500 °C, 700 °C and 900 °C. All samples exhibited a positive Seebeck coefficient over the range of pO2 and temperature examined, which indicates the predominance of p-type conduction. In all cases, conductivity increased with increasing pO2, ranging from a minimum of ~ 0.6 S/cm (x = 0, pO2 = 10− 5 atm, T = 900 °C) to a maximum of ~ 36 S/cm (x = 0.8, pO2 = 1 atm, and T = 900 °C). At low temperatures and high pO2, conductivity was approximately proportional to pO21/4, which was attributed to the reduction of B-site cations from their tetravalent to trivalent state. At low pO2 and high temperature, the conductivity exhibited positive deviations from the pO21/4 dependence. At 500 °C and x ≤ 0.6, the Seebeck coefficient (Q) decreased linearly with increasing log pO2. At 700 and 900 °C, Q vs. log pO2 curves exhibited maxima at 10− 3 < pO2 < 10− 1 atm, and the maxima shifted to higher pO2 as x increased. A simple p-type polaron hopping model, assuming negligible contribution from n-type or ionic carriers, was used to extract the carrier concentration of the x = 0.8 sample from the measured thermopower data. The calculated hole mobility for the x = 0.8 sample was less than 0.1 cm2/V-s, confirming a p-type polaron-hopping model. This analysis, as well as analysis of Jonker plots, suggested that hole mobility decreased with decreasing pO2.► Conductivity and Seebeck coefficient of BSCF was measured. ► BSCF materials are p-type polaron conductors at 500 °C–900 °C and 10–5 < pO2 < 1 atm. ► Seebeck coefficient and oxygen non-stoichiometry used to calculate valence state of Bn+. ► Hole mobility decreases with decreasing pO2.

Journal of Solid State Chemistry, 2011

The Ca2(ZnxFe2−x)O5 series was synthesized and characterized to determine the influence of zinc d... more The Ca2(ZnxFe2−x)O5 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 γ)s00 transition in Ca2Fe2O5 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 γ)s00 with γ=1/2. Both the Néel temperature and the onset temperature of the Pnma–Imma(0 0 γ)s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 °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 °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.Preferential substitution by zinc for iron at the tetrahedral sites of brownmillerite dicalcium ferrite modifies the high temperature Imma(0 0 γ)s00 phase from incommensurate to commensurate.► Preferential tetrahedral occupancy by zinc in brownmillerite dicalcium ferrite. ► Ca2Fe2O5 exhibits two additional phase transitions above 1000°C: a commensurately modulated Imma(0 0 γ)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 °C.

Solar Energy Materials and Solar Cells, 2009

Composite porcelain-enamel coatings consisting of spinel-type transition-metal-oxide pigments emb... more Composite porcelain-enamel coatings consisting of spinel-type transition-metal-oxide pigments embedded in a borosilicate-glass matrix were deposited on 321 stainless steel using screen-printing techniques and characterized using total reflectance over the spectral range of 200 nm to 25 mm. The composite coatings exhibited moderate spectral selectivity and excellent thermal stability at 450 1C. Solar absorptance (a) ranged from 0.82 to 0.90 and calculated thermal emittance at 500 1C (e) ranged from 0.46 to 0.79. Both depended on coating thickness and pigment volume concentrations. As an example, the highest solar selectivity was measured in a 0.9 mm coating with a and e (500 1C) being 0.82 and 0.46, respectively.

Journal of Solid State Chemistry, 2010

Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (di... more Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion αL) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma–Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α2σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden–Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10−6 K−1) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers.Representative microstructure of Ca2Fe2O5 samples used for thermoelectrical measurements.