Christopher Knee - Academia.edu (original) (raw)

Papers by Christopher Knee

In a systematic study we investigate the effect of dopant level and hydration on the short-range ... more In a systematic study we investigate the effect of dopant level and hydration on the short-range structure of the proton conducting perovskite-type oxide BaInxZr1−xO3−x/2 (x = 0 − 0.75), using infrared and Raman spectroscopy. The results show that doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75 new bands appear and grow in intensity in both the IR and Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size difference between the In 3+ and Zr 4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O6 octahedra. Based on our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the local structural distortions propagate throughout the whole perovskite structu...

The magnetic interactions in the layered cobalt (III) oxychlorides, Sr2CoO3Cl and Sr3Co2O5Cl2, ha... more The magnetic interactions in the layered cobalt (III) oxychlorides, Sr2CoO3Cl and Sr3Co2O5Cl2, have been studied using constant wavelength neutron powder diffraction and inelastic time-of-flight neutron scattering. The materials crystallize with Ruddlesden-Popper structures and contain layers of CoO5 pyramids that form CoO2 sheets in the ab-plane separated along c by SrCl rocksalt layers. The phases display contrasting magnetic properties despite the probable presence of high spin Co^3+ (S = 2) in both compounds. Sr2CoO3Cl undergoes a transition to long range 3D antiferromagnetic (AFM) order at a TN = 330 K, preceded by strong diffuse scattering from 2D spin coherence. Sr3Co2O5Cl2 does not exhibit the expected long range ordered AFM ground state, and instead the spin correlation is limited to short range 2D interactions. The material's magnetism is rationalized based on competing FM and AFM coupling.

Physical Review B, 2006

... PHYSICAL REVIEW B 74, 134502 2006 Resonant two-phonon Raman scattering as a probe of hole cry... more ... PHYSICAL REVIEW B 74, 134502 2006 Resonant two-phonon Raman scattering as a probe of hole crystal formation in Sr14-xCaxCu24O41 Joakim Holmlund,1 Jakob Andreasson,1Christopher S. Knee,1 ... 27 MW McElfresh, JMD Coey, P. Strobel, and S. von Molnar, Phys. Rev. ...

Solid State Ionics

The proton conductivity and structural features of In3+ substituted BaZrO3 samples, i.e., BaZr1−x... more The proton conductivity and structural features of In3+ substituted BaZrO3 samples, i.e., BaZr1−xInxO3−δ, were investigated. Rietveld analysis of low temperature (10K) neutron powder diffraction data collected on as-prepared and deuterated samples confirmed cubic symmetry (space group Pm-3m) for all compositions. The level of oxygen vacancies refined in the as-prepared samples were in good agreement with the values expected to conserve charge neutrality, whilst an increase in oxygen occupancy, reflecting the incorporation of OD− species, was obtained for the deuterated materials. An expansion of the unit cell parameter, a, was observed as a function of In3+ doping as well as after the deuteration reaction. The conductivity of pre-hydrated and dry samples was measured using impedance methods. For 25% In-doped BaZrO3, the low T (300°C) conductivity of the heating cycle of the dried sample was greater than that of the cooling cycle of the pre-hydrated sample indicating a greater number...

Chemistry of Materials

A two-step process using liquid crystalline phases combined with controlled postcrystallization f... more A two-step process using liquid crystalline phases combined with controlled postcrystallization for the preparation of bone-like apatite has been developed. First, amorphous calcium phosphate (ACP) spherules with a diameter of 10.8 ± 1.4 nm and specific surface area (SSA) in the range of 150–170 m2/g were synthesized within a reverse hexagonal liquid crystalline (LC) phase. Second, the ACP spherules were dispersed and aged in Milli-Q water, where they crystallized into poorly crystalline apatite (PCA). The addition of heparin during aging was explored, which was shown to retard the ACP – PCA conversion. The particle formation within the LC phase was monitored using synchrotron small-angle X-ray scattering, and the formed materials were characterized by X-ray diffraction, conventional and high-resolution transmission electron microscopy, nitrogen adsorption, thermogravimetry with infrared-coupled analysis, and Raman spectroscopy. The PCA formed using the LC–aging route presented bone...

We study the phonon spectrum of the iron-pnictide superconductors, (Ce,Nd)O1-xFxFeAs, using Raman... more We study the phonon spectrum of the iron-pnictide superconductors, (Ce,Nd)O1-xFxFeAs, using Raman spectroscopy. Based on the temperature dependent softening of the out of plane optical Fe-mode (B1g at gamma) we estimate the magnitude of the cubic anharmonicity of the Fe-As bond by calculating the self-energy due to phonon-phonon interactions. This also gives an estimate of the lattice expansion or contraction

Solid State Ionics, 2006

Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1−xI... more Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1−xInxO3−δ (0.0≤x≤0.75). Analysis of X-ray powder diffraction (XRPD) data reveals that the unit cell parameter, a, increases linearly with an increased Indium concentration. XRPD data was also used to demonstrate the completion of sample hydration, which was reached when the materials showed a set of single-phase Bragg-peaks.

Ceramic Engineering and Science Proceedings, 2006

... ''A. Novak “Hydrogen bonding in Solids&... more ... ''A. Novak “Hydrogen bonding in Solids'' Struct.Bond. 18, 177-216 (1974) I'M. Karlsson, A. Matic, L.Borjesson, D. Engberg, M. Bjorketun, P. Sundell, G. Wahnstrom, I. Ahmed, SG Eriksson, P.Berastegui, 'Vibrational Properties of Protons in Hydrated Baln,Zrl.,03. ... P. Berastegui, LG. ...

Dalton transactions (Cambridge, England : 2003), Jan 25, 2015

The crystal structure of the proton conducting perovskite BaCe0.8Y0.2O3-δ (BCY20) has been studie... more The crystal structure of the proton conducting perovskite BaCe0.8Y0.2O3-δ (BCY20) has been studied via high-resolution in situ neutron diffraction performed in controlled dry and humid (heavy water) oxygen flow. Two phase transitions, cubic Pm3[combining macron]m→R3[combining macron]c (775 °C)→Imma (250 °C) were observed on cooling from 1000 °C in dry O2. A significant shift of the phase stability fields was observed on cooling in wet oxygen (pD2O ≈ 0.2 atm) with the R3[combining macron]c structure stabilised at 900 °C, and the R3[combining macron]c→Imma transition occurring at 675 °C. On cooling below 400 °C a monoclinic, I2/m, phase started to appear. The structural dependence on hydration level is primarily due to the de-stabilisation of the correlated, octahedra tilts as a consequence of structural relaxation around the oxygen vacancies present in the non-hydrated phase. The tendency of hydrated BaCe0.8Y0.2O3-δ to show octahedral tilting is also found to be enhanced, indicating ...

Inorganic chemistry, Jan 16, 2015

This article establishes the effect of structure and composition on water uptake and the hydratio... more This article establishes the effect of structure and composition on water uptake and the hydration and proton transport properties of the oxygen-deficient perovskite series BaTi1-x(In,Sc)xO3-x/2, with 0.2 ≤ x ≤ 0.7. The equilibrium water uptake is determined by thermogravimetry, while combining thermogravimetry with differential scanning calorimetry allows for direct determination of the materials' hydration thermodynamics. Proton and oxide ion transport properties are characterized by means of ac impedance measurements up to 1000 °C. In general, the hydration thermodynamics of the scandates are more favorable than that of the indates and are also affected by changes in crystal structure throughout the series. The more favorable hydration thermodynamics of cubic scandates increase their proton conductivity at higher temperatures compared to their indate counterparts. In contrast to the BaTi1-xInxO3-x/2 series, the BaTi1-xScxO3-x/2 (0.5 ≤ x ≤ 0.7) materials retain their cubic str...

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT 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.

ABSTRACT The resonance behavior of the oxygen breathing mode at 700 cm(- 1) and its higher orders... more ABSTRACT The resonance behavior of the oxygen breathing mode at 700 cm(- 1) and its higher orders is studied between 1.8 eV (676 nm) and 4.2 eV (300 nm) in the perovskite LaFe(0.5)Cr(0.5)O(3). The Franck-Condon induced higher order scattering present in the x=0.1, 0.5 and 0.9 compounds dominates the Raman spectrum in the visible energy region while a feature in the 1400 cm-1 energy region dominates using UV lasers. The energy location of this peak coincides both with the second order Franck-Condon mode as well as similar feature seen in the x=0 and 1 compounds (and to some extent in the low doping compounds (x=0.02, 0.04, 0.06 and 0.08)) using the 2.41 eV (lambda=514) laser, believed to be a two-magnon caused by a spin-flip excitation in the AFM spin-state. Thus the complex magnetism in the Fe/Cr perovskite is likely to be influenced by the competition between the magnetically ordered state and the lattice dynamics through the resonant Franck- Condon effect.

We investigate the local structure and dehydration properties of the proton conducting brownmille... more We investigate the local structure and dehydration properties of the proton conducting brownmillerite type oxide BaInO$_{3}$H, using variable temperature Raman spectroscopy and inelastic neutron scattering. Analysis of the room temperature spectra suggest that BaInO$_{3}$H can adopt three distinctly different, local, structures, depending on the level of hydration, whereas upon temperature increase, the material dehydrates gradually with increasing temperature. At a temperature of around 370 {\deg}C, corresponding to a hydration degree of about 35%, the material undergoes a phase transition towards an intermediate phase before reaching the fully dehydrated structure.

Chemical Engineering Communications, 2015

ABSTRACT Due to discrepancy in the standard enthalpy of formation, , of copper(II) aluminate (CuA... more ABSTRACT Due to discrepancy in the standard enthalpy of formation, , of copper(II) aluminate (CuAl2O4) reported in thermodynamic databases, the calculated reaction enthalpy, ΔHr, of CuAl2O4 with reducing gases varies considerably. In this work, the standard enthalpy of formation, , of CuAl2O4 is reassessed using the reaction enthalpy, ΔHr, of CuAl2O4 with CO measured by differential scanning calorimetry. A value of −1824.4 ± 4.1 kJ/mol was found for the standard enthalpy of formation, , of CuAl2O4.

ChemInform, 2008

Hydration, Structure, and Superconductivity of KOs2O6·nH2O. -KOs2O6 reversibly incorporates water... more Hydration, Structure, and Superconductivity of KOs2O6·nH2O. -KOs2O6 reversibly incorporates water molecules to produce KOs 2 O 6 ·0.1H 2 O through a structural mechanism that involves partial replacement of the potassium ions and expansion of the unit cell (space group Fd3m) as shown by variable temperature powder neutron and X-ray diffraction. Hydration has the effect of reducing the onset of superconducting behavior from a critical temperature of 10.25 K in fully dry KOs2O6 to 9.75 K in KOs 2 O 6 ·0.1H 2 O. -(GALATI, R.; SIMON, C.; KNEE, C. S.; HENRY, P. F.; RAINFORD, B. D.; WELLER*, M. T.; Chem. Mater.

Journal of Physics: Condensed Matter, 2013

Deuterated BaTi0.5In0.5O2.75 has been studied with neutron total (Bragg plus diffuse) scattering ... more Deuterated BaTi0.5In0.5O2.75 has been studied with neutron total (Bragg plus diffuse) scattering data, using both the Rietveld refinement method and the reverse Monte Carlo (RMC) modelling technique, to investigate the preferred proton site and its local structural environment. The Rietveld analysis shows an excellent fit between experimental data and a long-range cubic description of the BaTi0.5In0.5O2.53(OD)0.44 perovskite structure containing a statistical distribution of Ti and In ions at the centre of regular (Ti/In)O6 octahedra. However, an RMC analysis of the data reveals substantial local structural features that reflect limitations of the Rietveld method for studies of this type. The Ti-O and In-O pair distribution functions given by the RMC analysis are markedly different from each other, with average Ti-O and In-O bond distances of 2.035 Å and 2.159 Å, respectively. The InO6 octahedra are regular in shape whereas the TiO6 octahedra are distorted. The average O-D bond distance is roughly 0.96 Å, and the preferred deuteron sites have a second nearest oxygen distance of 2.13 Å, which confirms localized tilting of the deuteron and indicates a substantial degree of hydrogen bonding. The impact of octahedral distortion and hydrogen bonding on the proton conduction mechanism is discussed.

Dalton transactions (Cambridge, England : 2003), Jan 28, 2014

BaTi1-xScxO3-δ (x = 0.1-0.8) was prepared via solid state reaction. High resolution X-ray powder ... more BaTi1-xScxO3-δ (x = 0.1-0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti(4+) for Sc(3+) gives a hexagonal perovskite structure, whereas high substitution (x = 0.5-0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H2O and D2O, conditions for BaTi1-xScxO3-δ (x = 0.2, 0.6 and 0.7). In the temperature range of 150-600 °C, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8Sc0.2O3-δ is approx. two orders of ma...

Physical Review B, 2003

The temperature dependence of the nuclear and magnetic structure of the cobalt oxychloride Sr 2 C... more The temperature dependence of the nuclear and magnetic structure of the cobalt oxychloride Sr 2 CoO 3 Cl has been studied using neutron powder diffraction. The material crystallizes with a structure related to K 2 NiF 4 and contains two-dimensional ͑2D͒ layers of CoO 5 square pyramids that are segregated along z by alternate rocksalt SrCl and SrO blocks. The development of magnetic Bragg scattering indicates that the compound orders antiferromagnetically with a T N ϭ330(5) K. The phase adopts a collinear magnetic structure related to the nuclear cell by the propagation vector kϭ( 1 2 , PHYSICAL REVIEW B 68, 174407 ͑2003͒

In a systematic study we investigate the effect of dopant level and hydration on the short-range ... more In a systematic study we investigate the effect of dopant level and hydration on the short-range structure of the proton conducting perovskite-type oxide BaInxZr1−xO3−x/2 (x = 0 − 0.75), using infrared and Raman spectroscopy. The results show that doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75 new bands appear and grow in intensity in both the IR and Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size difference between the In 3+ and Zr 4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O6 octahedra. Based on our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the local structural distortions propagate throughout the whole perovskite structu...

The magnetic interactions in the layered cobalt (III) oxychlorides, Sr2CoO3Cl and Sr3Co2O5Cl2, ha... more The magnetic interactions in the layered cobalt (III) oxychlorides, Sr2CoO3Cl and Sr3Co2O5Cl2, have been studied using constant wavelength neutron powder diffraction and inelastic time-of-flight neutron scattering. The materials crystallize with Ruddlesden-Popper structures and contain layers of CoO5 pyramids that form CoO2 sheets in the ab-plane separated along c by SrCl rocksalt layers. The phases display contrasting magnetic properties despite the probable presence of high spin Co^3+ (S = 2) in both compounds. Sr2CoO3Cl undergoes a transition to long range 3D antiferromagnetic (AFM) order at a TN = 330 K, preceded by strong diffuse scattering from 2D spin coherence. Sr3Co2O5Cl2 does not exhibit the expected long range ordered AFM ground state, and instead the spin correlation is limited to short range 2D interactions. The material's magnetism is rationalized based on competing FM and AFM coupling.

Physical Review B, 2006

... PHYSICAL REVIEW B 74, 134502 2006 Resonant two-phonon Raman scattering as a probe of hole cry... more ... PHYSICAL REVIEW B 74, 134502 2006 Resonant two-phonon Raman scattering as a probe of hole crystal formation in Sr14-xCaxCu24O41 Joakim Holmlund,1 Jakob Andreasson,1Christopher S. Knee,1 ... 27 MW McElfresh, JMD Coey, P. Strobel, and S. von Molnar, Phys. Rev. ...

Solid State Ionics

The proton conductivity and structural features of In3+ substituted BaZrO3 samples, i.e., BaZr1−x... more The proton conductivity and structural features of In3+ substituted BaZrO3 samples, i.e., BaZr1−xInxO3−δ, were investigated. Rietveld analysis of low temperature (10K) neutron powder diffraction data collected on as-prepared and deuterated samples confirmed cubic symmetry (space group Pm-3m) for all compositions. The level of oxygen vacancies refined in the as-prepared samples were in good agreement with the values expected to conserve charge neutrality, whilst an increase in oxygen occupancy, reflecting the incorporation of OD− species, was obtained for the deuterated materials. An expansion of the unit cell parameter, a, was observed as a function of In3+ doping as well as after the deuteration reaction. The conductivity of pre-hydrated and dry samples was measured using impedance methods. For 25% In-doped BaZrO3, the low T (300°C) conductivity of the heating cycle of the dried sample was greater than that of the cooling cycle of the pre-hydrated sample indicating a greater number...

Chemistry of Materials

A two-step process using liquid crystalline phases combined with controlled postcrystallization f... more A two-step process using liquid crystalline phases combined with controlled postcrystallization for the preparation of bone-like apatite has been developed. First, amorphous calcium phosphate (ACP) spherules with a diameter of 10.8 ± 1.4 nm and specific surface area (SSA) in the range of 150–170 m2/g were synthesized within a reverse hexagonal liquid crystalline (LC) phase. Second, the ACP spherules were dispersed and aged in Milli-Q water, where they crystallized into poorly crystalline apatite (PCA). The addition of heparin during aging was explored, which was shown to retard the ACP – PCA conversion. The particle formation within the LC phase was monitored using synchrotron small-angle X-ray scattering, and the formed materials were characterized by X-ray diffraction, conventional and high-resolution transmission electron microscopy, nitrogen adsorption, thermogravimetry with infrared-coupled analysis, and Raman spectroscopy. The PCA formed using the LC–aging route presented bone...

We study the phonon spectrum of the iron-pnictide superconductors, (Ce,Nd)O1-xFxFeAs, using Raman... more We study the phonon spectrum of the iron-pnictide superconductors, (Ce,Nd)O1-xFxFeAs, using Raman spectroscopy. Based on the temperature dependent softening of the out of plane optical Fe-mode (B1g at gamma) we estimate the magnitude of the cubic anharmonicity of the Fe-As bond by calculating the self-energy due to phonon-phonon interactions. This also gives an estimate of the lattice expansion or contraction

Solid State Ionics, 2006

Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1−xI... more Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1−xInxO3−δ (0.0≤x≤0.75). Analysis of X-ray powder diffraction (XRPD) data reveals that the unit cell parameter, a, increases linearly with an increased Indium concentration. XRPD data was also used to demonstrate the completion of sample hydration, which was reached when the materials showed a set of single-phase Bragg-peaks.

Ceramic Engineering and Science Proceedings, 2006

... ''A. Novak “Hydrogen bonding in Solids&... more ... ''A. Novak “Hydrogen bonding in Solids'' Struct.Bond. 18, 177-216 (1974) I'M. Karlsson, A. Matic, L.Borjesson, D. Engberg, M. Bjorketun, P. Sundell, G. Wahnstrom, I. Ahmed, SG Eriksson, P.Berastegui, 'Vibrational Properties of Protons in Hydrated Baln,Zrl.,03. ... P. Berastegui, LG. ...

Dalton transactions (Cambridge, England : 2003), Jan 25, 2015

The crystal structure of the proton conducting perovskite BaCe0.8Y0.2O3-δ (BCY20) has been studie... more The crystal structure of the proton conducting perovskite BaCe0.8Y0.2O3-δ (BCY20) has been studied via high-resolution in situ neutron diffraction performed in controlled dry and humid (heavy water) oxygen flow. Two phase transitions, cubic Pm3[combining macron]m→R3[combining macron]c (775 °C)→Imma (250 °C) were observed on cooling from 1000 °C in dry O2. A significant shift of the phase stability fields was observed on cooling in wet oxygen (pD2O ≈ 0.2 atm) with the R3[combining macron]c structure stabilised at 900 °C, and the R3[combining macron]c→Imma transition occurring at 675 °C. On cooling below 400 °C a monoclinic, I2/m, phase started to appear. The structural dependence on hydration level is primarily due to the de-stabilisation of the correlated, octahedra tilts as a consequence of structural relaxation around the oxygen vacancies present in the non-hydrated phase. The tendency of hydrated BaCe0.8Y0.2O3-δ to show octahedral tilting is also found to be enhanced, indicating ...

Inorganic chemistry, Jan 16, 2015

This article establishes the effect of structure and composition on water uptake and the hydratio... more This article establishes the effect of structure and composition on water uptake and the hydration and proton transport properties of the oxygen-deficient perovskite series BaTi1-x(In,Sc)xO3-x/2, with 0.2 ≤ x ≤ 0.7. The equilibrium water uptake is determined by thermogravimetry, while combining thermogravimetry with differential scanning calorimetry allows for direct determination of the materials' hydration thermodynamics. Proton and oxide ion transport properties are characterized by means of ac impedance measurements up to 1000 °C. In general, the hydration thermodynamics of the scandates are more favorable than that of the indates and are also affected by changes in crystal structure throughout the series. The more favorable hydration thermodynamics of cubic scandates increase their proton conductivity at higher temperatures compared to their indate counterparts. In contrast to the BaTi1-xInxO3-x/2 series, the BaTi1-xScxO3-x/2 (0.5 ≤ x ≤ 0.7) materials retain their cubic str...

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT 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.

ABSTRACT The resonance behavior of the oxygen breathing mode at 700 cm(- 1) and its higher orders... more ABSTRACT The resonance behavior of the oxygen breathing mode at 700 cm(- 1) and its higher orders is studied between 1.8 eV (676 nm) and 4.2 eV (300 nm) in the perovskite LaFe(0.5)Cr(0.5)O(3). The Franck-Condon induced higher order scattering present in the x=0.1, 0.5 and 0.9 compounds dominates the Raman spectrum in the visible energy region while a feature in the 1400 cm-1 energy region dominates using UV lasers. The energy location of this peak coincides both with the second order Franck-Condon mode as well as similar feature seen in the x=0 and 1 compounds (and to some extent in the low doping compounds (x=0.02, 0.04, 0.06 and 0.08)) using the 2.41 eV (lambda=514) laser, believed to be a two-magnon caused by a spin-flip excitation in the AFM spin-state. Thus the complex magnetism in the Fe/Cr perovskite is likely to be influenced by the competition between the magnetically ordered state and the lattice dynamics through the resonant Franck- Condon effect.

We investigate the local structure and dehydration properties of the proton conducting brownmille... more We investigate the local structure and dehydration properties of the proton conducting brownmillerite type oxide BaInO$_{3}$H, using variable temperature Raman spectroscopy and inelastic neutron scattering. Analysis of the room temperature spectra suggest that BaInO$_{3}$H can adopt three distinctly different, local, structures, depending on the level of hydration, whereas upon temperature increase, the material dehydrates gradually with increasing temperature. At a temperature of around 370 {\deg}C, corresponding to a hydration degree of about 35%, the material undergoes a phase transition towards an intermediate phase before reaching the fully dehydrated structure.

Chemical Engineering Communications, 2015

ABSTRACT Due to discrepancy in the standard enthalpy of formation, , of copper(II) aluminate (CuA... more ABSTRACT Due to discrepancy in the standard enthalpy of formation, , of copper(II) aluminate (CuAl2O4) reported in thermodynamic databases, the calculated reaction enthalpy, ΔHr, of CuAl2O4 with reducing gases varies considerably. In this work, the standard enthalpy of formation, , of CuAl2O4 is reassessed using the reaction enthalpy, ΔHr, of CuAl2O4 with CO measured by differential scanning calorimetry. A value of −1824.4 ± 4.1 kJ/mol was found for the standard enthalpy of formation, , of CuAl2O4.

ChemInform, 2008

Hydration, Structure, and Superconductivity of KOs2O6·nH2O. -KOs2O6 reversibly incorporates water... more Hydration, Structure, and Superconductivity of KOs2O6·nH2O. -KOs2O6 reversibly incorporates water molecules to produce KOs 2 O 6 ·0.1H 2 O through a structural mechanism that involves partial replacement of the potassium ions and expansion of the unit cell (space group Fd3m) as shown by variable temperature powder neutron and X-ray diffraction. Hydration has the effect of reducing the onset of superconducting behavior from a critical temperature of 10.25 K in fully dry KOs2O6 to 9.75 K in KOs 2 O 6 ·0.1H 2 O. -(GALATI, R.; SIMON, C.; KNEE, C. S.; HENRY, P. F.; RAINFORD, B. D.; WELLER*, M. T.; Chem. Mater.

Journal of Physics: Condensed Matter, 2013

Deuterated BaTi0.5In0.5O2.75 has been studied with neutron total (Bragg plus diffuse) scattering ... more Deuterated BaTi0.5In0.5O2.75 has been studied with neutron total (Bragg plus diffuse) scattering data, using both the Rietveld refinement method and the reverse Monte Carlo (RMC) modelling technique, to investigate the preferred proton site and its local structural environment. The Rietveld analysis shows an excellent fit between experimental data and a long-range cubic description of the BaTi0.5In0.5O2.53(OD)0.44 perovskite structure containing a statistical distribution of Ti and In ions at the centre of regular (Ti/In)O6 octahedra. However, an RMC analysis of the data reveals substantial local structural features that reflect limitations of the Rietveld method for studies of this type. The Ti-O and In-O pair distribution functions given by the RMC analysis are markedly different from each other, with average Ti-O and In-O bond distances of 2.035 Å and 2.159 Å, respectively. The InO6 octahedra are regular in shape whereas the TiO6 octahedra are distorted. The average O-D bond distance is roughly 0.96 Å, and the preferred deuteron sites have a second nearest oxygen distance of 2.13 Å, which confirms localized tilting of the deuteron and indicates a substantial degree of hydrogen bonding. The impact of octahedral distortion and hydrogen bonding on the proton conduction mechanism is discussed.

Dalton transactions (Cambridge, England : 2003), Jan 28, 2014

BaTi1-xScxO3-δ (x = 0.1-0.8) was prepared via solid state reaction. High resolution X-ray powder ... more BaTi1-xScxO3-δ (x = 0.1-0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti(4+) for Sc(3+) gives a hexagonal perovskite structure, whereas high substitution (x = 0.5-0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H2O and D2O, conditions for BaTi1-xScxO3-δ (x = 0.2, 0.6 and 0.7). In the temperature range of 150-600 °C, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8Sc0.2O3-δ is approx. two orders of ma...

Physical Review B, 2003

The temperature dependence of the nuclear and magnetic structure of the cobalt oxychloride Sr 2 C... more The temperature dependence of the nuclear and magnetic structure of the cobalt oxychloride Sr 2 CoO 3 Cl has been studied using neutron powder diffraction. The material crystallizes with a structure related to K 2 NiF 4 and contains two-dimensional ͑2D͒ layers of CoO 5 square pyramids that are segregated along z by alternate rocksalt SrCl and SrO blocks. The development of magnetic Bragg scattering indicates that the compound orders antiferromagnetically with a T N ϭ330(5) K. The phase adopts a collinear magnetic structure related to the nuclear cell by the propagation vector kϭ( 1 2 , PHYSICAL REVIEW B 68, 174407 ͑2003͒