Mats Johnsson - Academia.edu (original) (raw)
Papers by Mats Johnsson
Nanomaterials, 2021
Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is ... more Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is an essential step for advancing the TE technology. We present here very rapid and effective methods for the synthesis of nanostructured bismuth telluride materials with promising TE performance. The methodology is based on an effective volume heating using microwaves, leading to highly crystalline nanostructured powders, in a reaction duration of two minutes. As the solvents, we demonstrate that water with a high dielectric constant is as good a solvent as ethylene glycol (EG) for the synthetic process, providing a greener reaction media. Crystal structure, crystallinity, morphology, microstructure and surface chemistry of these materials were evaluated using XRD, SEM/TEM, XPS and zeta potential characterization techniques. Nanostructured particles with hexagonal platelet morphology were observed in both systems. Surfaces show various degrees of oxidation, and signatures of the precursor...
Nanomaterials, 2020
Reduced energy consumption and environmentally friendly, abundant constituents are gaining more a... more Reduced energy consumption and environmentally friendly, abundant constituents are gaining more attention for the synthesis of energy materials. A rapid, highly scalable, and process-temperature-sensitive solution synthesis route is demonstrated for the fabrication of thermoelectric (TE) Cu2−xSe. The process relies on readily available precursors and microwave-assisted thermolysis, which is sensitive to reaction conditions; yielding Cu1.8Se at 200 °C and Cu2Se at 250 °C within 6–8 min reaction time. Transmission electron microscopy (TEM) revealed crystalline nature of as-made particles with irregular truncated morphology, which exhibit a high phase purity as identified by X-ray powder diffraction (XRPD) analysis. Temperature-dependent transport properties were characterized via electrical conductivity, Seebeck coefficient, and thermal diffusivity measurements. Subsequent to spark plasma sintering, pure Cu1.8Se exhibited highly compacted and oriented grains that were similar in size ...
Applied Sciences, 2020
The solution synthesis route as a scalable bottom-up synthetic method possesses significant advan... more The solution synthesis route as a scalable bottom-up synthetic method possesses significant advantages for synthesizing nanostructured bulk thermoelectric (TE) materials with improved performance. Tuning the composition of the materials directly in the solution, without needing any further processing, is important for adjusting the dominant carrier type. Here, we report a very rapid (2 min) and high yield (>8 g/batch) synthetic method using microwave-assisted heating, for the controlled growth of Bi2–xSbxTe3 (x: 0–2) nanoplatelets. Resultant materials exhibit a high crystallinity and phase purity, as characterized by XRD, and platelet morphology, as revealed by SEM. Surface chemistry of as-made materials showed a mixture of metallic and oxide phases, as evidenced by XPS. Zeta-potential analysis exhibited a systematic change of isoelectric point as a function of the material composition. As-made materials were directly sintered into pellets by using spark plasma sintering process....
![Research paper thumbnail of Synthesis and Magnetic Properties of the KCu(IO3)3 Compound with [CuO5]∞ Chains](https://attachments.academia-assets.com/98101984/thumbnails/1.jpg)
](ACS Omega, 2019
The new quaternary iodate KCu(IO 3) 3 has been prepared by hydrothermal synthesis. KCu(IO 3) 3 cr... more The new quaternary iodate KCu(IO 3) 3 has been prepared by hydrothermal synthesis. KCu(IO 3) 3 crystallizes in the monoclinic space group P2 1 / n with unit cell parameters a = 9.8143(4) Å, b = 8.2265(4) Å, c = 10.8584(5) Å, β = 91.077(2)°, and z = 4. The crystals are light blue and translucent. There are three main building units making up the crystal structure: [KO 10 ] irregular polyhedra, [CuO 6 ] distorted octahedra, and [IO 3 ] trigonal pyramids. The Jahn−Teller elongated [CuO 6 ] octahedra connect to each other via corner sharing to form [CuO 5 ] ∞ zigzag chains along [010]; the other building blocks separate these chains. The Raman modes can be divided into four groups; the lower two groups into mainly lattice modes involving K and Cu displacements and the upper two groups into mainly bending and stretching modes of [IO 3 E], where E represents a lone pair of electron. At low temperatures, the magnetic susceptibility is characterized by a broad maximum centered at ∼5.4 K, characteristic for antiferromagnetic short-range ordering. Long-range magnetic ordering at T C = 1.32 K is clearly evidenced by a sharp anomaly in the heat capacity. The magnetic susceptibility can be very well described by a spin S = 1/2 antiferromagnetic Heisenberg chain with a nearest-neighbor spin exchange of ∼8.9 K.
Inorganic Chemistry, 2018
Single crystals of the new compound Cu 2 (SeO 3)F 2 were successfully synthesized via a hydrother... more Single crystals of the new compound Cu 2 (SeO 3)F 2 were successfully synthesized via a hydrothermal method, and the crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma with the unit cell parameters a = 7.066(4) Å, b = 9.590(4) Å, and c = 5.563(3) Å. Cu 2 (SeO 3)F 2 is isostructural with the previously described compounds Co 2 TeO 3 F 2 and CoSeO 3 F 2. The crystal structure comprises a framework of corner-and edge-sharing distorted [CuO 3 F 3 ] octahedra, within which [SeO 3 ] trigonal pyramids are present in voids and are connected to [CuO 3 F 3 ] octahedra by corner sharing. The presence of a single local environment in both the 19 F and 77 Se solid-state MAS NMR spectra supports the hypothesis that O and F do not mix at the same crystallographic positions. Also the specific phonon modes observed with Raman scattering support the coordination around the cations. At high temperatures the magnetic susceptibility follows the Curie−Weiss law with Curie temperature of Θ = −173(2) K and an effective magnetic moment of μ eff ∼ 2.2 μ B. Antiferromagnetic ordering below ∼44 K is indicated by a peak in the magnetic susceptibility. A second though smaller peak at ∼16 K is tentatively ascribed to a magnetic reorientation transition. Both transitions are also confirmed by heat capacity measurements. Raman scattering experiments propose a structural phase instability in the temperature range 6−50 K based on phonon anomalies. Further changes in the Raman shift of modes at ∼46 K and ∼16 K arise from transitions of the magnetic lattice in accordance with the susceptibility and heat capacity measurements.
Crystals, 2019
Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 °C. The cry... more Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 °C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = 4.0003(2) Å, b = 7.3355(3) Å, c = 12.6985(6) Å, β = 90°. The crystal structure comprises five crystallographically independent M atoms and one Sb3+ atom, M atoms are of two kinds of partially occupied sites Mo6+ and Fe3+. The building blocks consist of [SbO3O0.5O0.5E] octahedra (E = lone electron pair) and [(Mo/Fe)O6] octahedra. The M = (Mo, Fe) and O atoms are arranged in a distorted hexagonal 2D-net, not the Sb atoms. The distortion of the net and consequently the symmetry reduction results mainly from the location of the Sb atoms. Disorder manifests itself as a splitting of the metal sites and as a consequent shortening of the Mo–Fe distances. Six (Mo/Fe)O6 octahedra are connected to form a pseudohexagonal channel. ...
Physical Review B, 2003
We present a comprehensive study of the coupled tetrahedra-compound Cu2Te2O5Br2 by theory and exp... more We present a comprehensive study of the coupled tetrahedra-compound Cu2Te2O5Br2 by theory and experiments in external magnetic fields. We report the observation of a longitudinal magnon in Raman scattering in the ordered state close to quantum criticality. We show that the excited tetrahedral-singlet sets the energy scale for the magnetic ordering temperature TN. This energy is determined experimentally. The ordering temperature TN has an inverse-log dependence on the coupling parameters near quantum criticality.
Dalton transactions (Cambridge, England : 2003), Jan 26, 2016
The single crystals of the new isostructural compounds Sb3O4F and Y0.5Sb2.5O4F and the two previo... more The single crystals of the new isostructural compounds Sb3O4F and Y0.5Sb2.5O4F and the two previously known compounds M-SbOF and α-Sb3O2F5 were successfully grown by a hydrothermal technique at 230 °C. The new compound Sb3O4F crystallizes in the monoclinic space group P21/c; a = 5.6107(5) Å, b = 4.6847(5) Å, c = 20.2256(18) Å, β = 94.145(8)°, z = 4. The replacing part of Sb with Y means a slight increase in the unit cell dimensions. The compounds M-SbOF and α-Sb3O2F5 have not been grown as single crystals before and it can be concluded that hydrothermal synthesis has proved to be a suitable technique for growing single crystals of antimony oxofluorides because of the relatively low solubility of such compounds compared to other antimony oxohalides that most often have been synthesised at high temperatures by solid state reactions or gas-solid reactions.
Energy Harvesting and Systems, 2015
During the last decade oxide-based thermoelectric materials have received increased attention due... more During the last decade oxide-based thermoelectric materials have received increased attention due to their high stability and thermal robustness at high temperatures as well as the availability and nontoxic nature of a number of promising candidates. In the present study we are investigating the thermoelectric properties of an n-type La-substituted SrTiO
Handbook of Magnetism and Advanced Magnetic Materials, 2007
Despite the simplicity of the original perovskite crystal structure, this family of compounds sho... more Despite the simplicity of the original perovskite crystal structure, this family of compounds shows an enormous variety of structural modifications and variants. In the following, we will describe several examples of perovskites, their structural variants and discuss the implications of distortions and non-stoichiometry on their electronic and magnetic properties.
Journal of Alloys and Compounds, 2015
Thermoelectric is a promising technology that can convert temperature differences to electricity ... more Thermoelectric is a promising technology that can convert temperature differences to electricity (or vice versa). However, their relatively low efficiencies limit their applications to thermoelectric power generation systems. Therefore, low cost and high performance are important prerequisites for the application of thermoelectric materials to automotive thermoelectric generators. Silicide-based thermoelectric materials are good candidates for such applications. Recently, the thermoelectric performances of silicide-based thermoelectric materials have been significantly improved. However, increasing the thermoelectric performance of the materials while ensuring mechanical reliability remains a challenge. This review summarizes the preparation and design guidelines for silicide-based thermoelectric nanocomposites, as well as our recent progress in the development of nanocomposites with high thermoelectric performances or high mechanical reliabilities.
Journal of Alloys and Compounds, 2014
Nanostructured powders of thermoelectric (TE) CoSb 3 compounds were synthesized using a chemical ... more Nanostructured powders of thermoelectric (TE) CoSb 3 compounds were synthesized using a chemical alloying method. This method involved co-precipitation of oxalate precursors in aqueous solution with controlled pH, followed by thermochemical treatments including calcination and reduction to produce stoichiometric nanostructured CoSb 3. Moreover, CoSb 3 nanoparticles were consolidated by spark plasma sintering (SPS) with a very brief processing time. Very high compaction densities (>95%) were achieved and the grain growth was almost negligible during consolidation. An iterative procedure was developed to maintain pre-consolidation particle size and to compensate Sb evaporation during reduction. Significant changes in particle size and morphology were observed, and the post-reduction cooling was found to be an important stage in the process. The spark plasma sintering (SPS) parameters were optimized to minimize the grain growth while achieving sufficient densification. Grain sizes in the range of 500 nm to 1 lm, with compaction density of 95-98% were obtained. Preliminary measurements of thermal diffusivity and conductivity showed the dependence on grain size as well as on porosity. TE transport properties were measured in the temperature range of 300-650 K. Sample showed p-type behavior with a positive Seebeck coefficient, which increases with increasing temperature. Electrical conductivity measurements indicate metallic behavior and it decreases with increasing temperature. Thermal conductivity also decreases with increasing temperature and major contribution is due to the lattice component. A TE figure of merit of 0.15 was achieved for high purity CoSb 3 nanostructured TE material at 650 K and these results are comparable with the values reported for the best unfilled/undoped CoSb 3 in the literature.
MRS Proceedings, 2012
ABSTRACTSkutterudites are known to be efficient thermoelectric (TE) materials in the temperature ... more ABSTRACTSkutterudites are known to be efficient thermoelectric (TE) materials in the temperature range from 600 K to 900 K. Dimensionless figure of merit (ZT) for filled skutterudite TE materials have been reported as ca. 1 at 800 K. Novel nano- engineering approaches and filling of the skutterudites crystal can further improve the transport properties and ultimately the ZT. Although classified among the promising TE materials, research on their large-scale production via bottom up synthetic routes is rather limited. In this work, large quantity of cobalt antimonide (CoSb3) based skutterudites nanopowder (NP) was fabricated through a room temperature co-precipitation precursor method. Dried precipitates were process by thermo-chemical treatment steps including calcination (in air) and reduction (in hydrogen). CoSb3 NPs were then mixed with silver (Ag) nanoparticles at different weight percentages (1%, 5% and 10% by wt) to form nanocomposites. Skutterudite NP was then consolidated by...
RSC Advances, 2012
For the preparation of electron conducting material the following chemicals, all from Sigma-Aldri... more For the preparation of electron conducting material the following chemicals, all from Sigma-Aldrich Company were used: 6.75 g of Ce(N0 3) 3 • 6H 2 0 0.75 g of Sm(N0 3) 3 • 6H 2 0 1.25 g of Zn(N0 3) 2 • 6H 2 0 1.00 g of Sr(N0 3) 2 1.575 g of Li 2 CO 3 8.25 g of NiCO 3 •2Ni(OH) 2 • xH 2 O 2.525 g of CuCO 3 • Cu(OH) 2 0.0125g of SrCO 3 Solid state reaction method has been used with one time intermediate grindings at 800 o C for 4 h.
Journal of Materials Science, 2014
Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compounds doped w... more Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compounds doped with various rare-earth elements with high purity and homogeneity, which can be processed under hydrogen into nanostructured oxide-dispersed tungsten composite powders having several potential applications. However, hydrogen reduction of doped tungsten oxide compounds is rather complex, affecting the morphology and composition of the final powder. In this study, we have investigated the reduction of tungstic acid in the presence of Y and we provide the experimental evidence that Y 2 O 3 can be separated from Y-doped tungstic acid via hydrogen reduction to produce Y 2 O 3-W powders. The processed powders were further consolidated by spark plasma sintering at different temperatures and holding times at 75 MPa pressure and characterized. The optimized SPS conditions suggest sintering at 1400°C for 3 min holding time to achieve higher density composites with an optimum finer grain size (3 lm) and a hardness value up to 420 H V. Major grain growth takes place at temperatures above 1300°C during sintering. From the density values obtained, it is recommend to apply higher pressure before 900°C to obtain maximum density. Oxides inclusions present in the matrix were identified as Y 2 O 3 Á3WO 3 and Y 2 O 3 ÁWO 3 during high resolution microscopic investigations.
Physical Review Letters, 2001
Physical Review B, 2006
We investigated the magnetic properties of the system CuTe2O5 by susceptibility and electron spin... more We investigated the magnetic properties of the system CuTe2O5 by susceptibility and electron spin resonance measurements. The anisotropy of the effective g-factors and the ESR linewidth indicates that the anticipated structural dimer does not correspond to the singlet-forming magnetic dimer. Moreover, the spin susceptibility of CuTe2O5 can only be described by taking into account interdimer interactions of the same order of magnitude than the intradimer coupling. Analyzing the exchange couplings in the system we identify the strongest magnetic coupling between two Cu ions to be mediated by super-super exchange interaction via a bridging Te ligand, while the superexchange coupling between the Cu ions of the structural dimer only results in the second strongest coupling.
Physical Review B, 2006
The crystal structure of the copper(II) tellurium(IV) oxochloride Cu4Te5O12Cl4 (Cu-45124) is comp... more The crystal structure of the copper(II) tellurium(IV) oxochloride Cu4Te5O12Cl4 (Cu-45124) is composed of weakly coupled tetrahedral Cu clusters and shows crystallographic similarities with the intensively investigated compound Cu2Te2O5X2, with X = Cl, Br (Cu-2252). It differs from the latter by a larger separation of the tetrahedra within the crystallographic ab plane, that allows a more direct assignment of important inter-tetrahedra exchange paths and the existence of an inversion center. Magnetic susceptibility and specific heat evidence antiferromagnetic, frustrated correlations of the Cu spin moments and long range ordering with Tc=13.6 K. The entropy related to the transition is reduced due to quantum fluctuations. In Raman scattering a well structured low energy magnetic excitation is observed at energies of ≈50K (35cm −1). This energy scale is reduced as compared to Cu-2252.
Journal of Materials Science, 2012
ABSTRACT Recently magnesium silicide (Mg2Si) has received great interest from thermoelectric (TE)... more ABSTRACT Recently magnesium silicide (Mg2Si) has received great interest from thermoelectric (TE) society because of its non-toxicity, environmental friendliness, comparatively high abundance, and low production material cost as compared to other TE systems. It also exhibited promising transport properties, including high electrical conductivity and low thermal conductivity, which improved the overall TE performance (ZT). In this work, Mg2Si powder was obtained through high energy ball milling under inert atmosphere, starting from commercial magnesium silicide pieces (99.99 %, Alfa Aesar). To maintain fine microstructure of the powder, spark plasma sintering (SPS) process has been used for consolidation. The Mg2Si powder was filled in a graphite die to perform SPS and the influence of process parameters as temperature, heating rate, holding time and applied pressure on the microstructure, and densification of compacts were studied in detail. The aim of this study is to optimize SPS consolidation parameters for Mg2Si powder to achieve high density of compacts while maintaining the nanostructure. X-Ray diffraction (XRD) was utilized to investigate the crystalline phase of compacted samples and scanning and transmission electron microscopy (SEM & TEM) coupled with Energy-Dispersive X-ray Analysis (EDX) was used to evaluate the detailed microstructural and chemical composition, respectively. All sintered samples showed compaction density up to 98 %. Temperature dependent TE characteristics of SPS compacted Mg2Si as thermal conductivity, electrical resistivity, and Seebeck coefficient were measured over the temperature range of RT 600 °C for samples processed at 750 °C, reaching a final ZT of 0.14 at 600 °C.
Journal of Materials Chemistry, 2012
Nanomaterials, 2021
Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is ... more Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is an essential step for advancing the TE technology. We present here very rapid and effective methods for the synthesis of nanostructured bismuth telluride materials with promising TE performance. The methodology is based on an effective volume heating using microwaves, leading to highly crystalline nanostructured powders, in a reaction duration of two minutes. As the solvents, we demonstrate that water with a high dielectric constant is as good a solvent as ethylene glycol (EG) for the synthetic process, providing a greener reaction media. Crystal structure, crystallinity, morphology, microstructure and surface chemistry of these materials were evaluated using XRD, SEM/TEM, XPS and zeta potential characterization techniques. Nanostructured particles with hexagonal platelet morphology were observed in both systems. Surfaces show various degrees of oxidation, and signatures of the precursor...
Nanomaterials, 2020
Reduced energy consumption and environmentally friendly, abundant constituents are gaining more a... more Reduced energy consumption and environmentally friendly, abundant constituents are gaining more attention for the synthesis of energy materials. A rapid, highly scalable, and process-temperature-sensitive solution synthesis route is demonstrated for the fabrication of thermoelectric (TE) Cu2−xSe. The process relies on readily available precursors and microwave-assisted thermolysis, which is sensitive to reaction conditions; yielding Cu1.8Se at 200 °C and Cu2Se at 250 °C within 6–8 min reaction time. Transmission electron microscopy (TEM) revealed crystalline nature of as-made particles with irregular truncated morphology, which exhibit a high phase purity as identified by X-ray powder diffraction (XRPD) analysis. Temperature-dependent transport properties were characterized via electrical conductivity, Seebeck coefficient, and thermal diffusivity measurements. Subsequent to spark plasma sintering, pure Cu1.8Se exhibited highly compacted and oriented grains that were similar in size ...
Applied Sciences, 2020
The solution synthesis route as a scalable bottom-up synthetic method possesses significant advan... more The solution synthesis route as a scalable bottom-up synthetic method possesses significant advantages for synthesizing nanostructured bulk thermoelectric (TE) materials with improved performance. Tuning the composition of the materials directly in the solution, without needing any further processing, is important for adjusting the dominant carrier type. Here, we report a very rapid (2 min) and high yield (>8 g/batch) synthetic method using microwave-assisted heating, for the controlled growth of Bi2–xSbxTe3 (x: 0–2) nanoplatelets. Resultant materials exhibit a high crystallinity and phase purity, as characterized by XRD, and platelet morphology, as revealed by SEM. Surface chemistry of as-made materials showed a mixture of metallic and oxide phases, as evidenced by XPS. Zeta-potential analysis exhibited a systematic change of isoelectric point as a function of the material composition. As-made materials were directly sintered into pellets by using spark plasma sintering process....
ACS Omega, 2019
The new quaternary iodate KCu(IO 3) 3 has been prepared by hydrothermal synthesis. KCu(IO 3) 3 cr... more The new quaternary iodate KCu(IO 3) 3 has been prepared by hydrothermal synthesis. KCu(IO 3) 3 crystallizes in the monoclinic space group P2 1 / n with unit cell parameters a = 9.8143(4) Å, b = 8.2265(4) Å, c = 10.8584(5) Å, β = 91.077(2)°, and z = 4. The crystals are light blue and translucent. There are three main building units making up the crystal structure: [KO 10 ] irregular polyhedra, [CuO 6 ] distorted octahedra, and [IO 3 ] trigonal pyramids. The Jahn−Teller elongated [CuO 6 ] octahedra connect to each other via corner sharing to form [CuO 5 ] ∞ zigzag chains along [010]; the other building blocks separate these chains. The Raman modes can be divided into four groups; the lower two groups into mainly lattice modes involving K and Cu displacements and the upper two groups into mainly bending and stretching modes of [IO 3 E], where E represents a lone pair of electron. At low temperatures, the magnetic susceptibility is characterized by a broad maximum centered at ∼5.4 K, characteristic for antiferromagnetic short-range ordering. Long-range magnetic ordering at T C = 1.32 K is clearly evidenced by a sharp anomaly in the heat capacity. The magnetic susceptibility can be very well described by a spin S = 1/2 antiferromagnetic Heisenberg chain with a nearest-neighbor spin exchange of ∼8.9 K.
Inorganic Chemistry, 2018
Single crystals of the new compound Cu 2 (SeO 3)F 2 were successfully synthesized via a hydrother... more Single crystals of the new compound Cu 2 (SeO 3)F 2 were successfully synthesized via a hydrothermal method, and the crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma with the unit cell parameters a = 7.066(4) Å, b = 9.590(4) Å, and c = 5.563(3) Å. Cu 2 (SeO 3)F 2 is isostructural with the previously described compounds Co 2 TeO 3 F 2 and CoSeO 3 F 2. The crystal structure comprises a framework of corner-and edge-sharing distorted [CuO 3 F 3 ] octahedra, within which [SeO 3 ] trigonal pyramids are present in voids and are connected to [CuO 3 F 3 ] octahedra by corner sharing. The presence of a single local environment in both the 19 F and 77 Se solid-state MAS NMR spectra supports the hypothesis that O and F do not mix at the same crystallographic positions. Also the specific phonon modes observed with Raman scattering support the coordination around the cations. At high temperatures the magnetic susceptibility follows the Curie−Weiss law with Curie temperature of Θ = −173(2) K and an effective magnetic moment of μ eff ∼ 2.2 μ B. Antiferromagnetic ordering below ∼44 K is indicated by a peak in the magnetic susceptibility. A second though smaller peak at ∼16 K is tentatively ascribed to a magnetic reorientation transition. Both transitions are also confirmed by heat capacity measurements. Raman scattering experiments propose a structural phase instability in the temperature range 6−50 K based on phonon anomalies. Further changes in the Raman shift of modes at ∼46 K and ∼16 K arise from transitions of the magnetic lattice in accordance with the susceptibility and heat capacity measurements.
Crystals, 2019
Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 °C. The cry... more Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 °C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = 4.0003(2) Å, b = 7.3355(3) Å, c = 12.6985(6) Å, β = 90°. The crystal structure comprises five crystallographically independent M atoms and one Sb3+ atom, M atoms are of two kinds of partially occupied sites Mo6+ and Fe3+. The building blocks consist of [SbO3O0.5O0.5E] octahedra (E = lone electron pair) and [(Mo/Fe)O6] octahedra. The M = (Mo, Fe) and O atoms are arranged in a distorted hexagonal 2D-net, not the Sb atoms. The distortion of the net and consequently the symmetry reduction results mainly from the location of the Sb atoms. Disorder manifests itself as a splitting of the metal sites and as a consequent shortening of the Mo–Fe distances. Six (Mo/Fe)O6 octahedra are connected to form a pseudohexagonal channel. ...
Physical Review B, 2003
We present a comprehensive study of the coupled tetrahedra-compound Cu2Te2O5Br2 by theory and exp... more We present a comprehensive study of the coupled tetrahedra-compound Cu2Te2O5Br2 by theory and experiments in external magnetic fields. We report the observation of a longitudinal magnon in Raman scattering in the ordered state close to quantum criticality. We show that the excited tetrahedral-singlet sets the energy scale for the magnetic ordering temperature TN. This energy is determined experimentally. The ordering temperature TN has an inverse-log dependence on the coupling parameters near quantum criticality.
Dalton transactions (Cambridge, England : 2003), Jan 26, 2016
The single crystals of the new isostructural compounds Sb3O4F and Y0.5Sb2.5O4F and the two previo... more The single crystals of the new isostructural compounds Sb3O4F and Y0.5Sb2.5O4F and the two previously known compounds M-SbOF and α-Sb3O2F5 were successfully grown by a hydrothermal technique at 230 °C. The new compound Sb3O4F crystallizes in the monoclinic space group P21/c; a = 5.6107(5) Å, b = 4.6847(5) Å, c = 20.2256(18) Å, β = 94.145(8)°, z = 4. The replacing part of Sb with Y means a slight increase in the unit cell dimensions. The compounds M-SbOF and α-Sb3O2F5 have not been grown as single crystals before and it can be concluded that hydrothermal synthesis has proved to be a suitable technique for growing single crystals of antimony oxofluorides because of the relatively low solubility of such compounds compared to other antimony oxohalides that most often have been synthesised at high temperatures by solid state reactions or gas-solid reactions.
Energy Harvesting and Systems, 2015
During the last decade oxide-based thermoelectric materials have received increased attention due... more During the last decade oxide-based thermoelectric materials have received increased attention due to their high stability and thermal robustness at high temperatures as well as the availability and nontoxic nature of a number of promising candidates. In the present study we are investigating the thermoelectric properties of an n-type La-substituted SrTiO
Handbook of Magnetism and Advanced Magnetic Materials, 2007
Despite the simplicity of the original perovskite crystal structure, this family of compounds sho... more Despite the simplicity of the original perovskite crystal structure, this family of compounds shows an enormous variety of structural modifications and variants. In the following, we will describe several examples of perovskites, their structural variants and discuss the implications of distortions and non-stoichiometry on their electronic and magnetic properties.
Journal of Alloys and Compounds, 2015
Thermoelectric is a promising technology that can convert temperature differences to electricity ... more Thermoelectric is a promising technology that can convert temperature differences to electricity (or vice versa). However, their relatively low efficiencies limit their applications to thermoelectric power generation systems. Therefore, low cost and high performance are important prerequisites for the application of thermoelectric materials to automotive thermoelectric generators. Silicide-based thermoelectric materials are good candidates for such applications. Recently, the thermoelectric performances of silicide-based thermoelectric materials have been significantly improved. However, increasing the thermoelectric performance of the materials while ensuring mechanical reliability remains a challenge. This review summarizes the preparation and design guidelines for silicide-based thermoelectric nanocomposites, as well as our recent progress in the development of nanocomposites with high thermoelectric performances or high mechanical reliabilities.
Journal of Alloys and Compounds, 2014
Nanostructured powders of thermoelectric (TE) CoSb 3 compounds were synthesized using a chemical ... more Nanostructured powders of thermoelectric (TE) CoSb 3 compounds were synthesized using a chemical alloying method. This method involved co-precipitation of oxalate precursors in aqueous solution with controlled pH, followed by thermochemical treatments including calcination and reduction to produce stoichiometric nanostructured CoSb 3. Moreover, CoSb 3 nanoparticles were consolidated by spark plasma sintering (SPS) with a very brief processing time. Very high compaction densities (>95%) were achieved and the grain growth was almost negligible during consolidation. An iterative procedure was developed to maintain pre-consolidation particle size and to compensate Sb evaporation during reduction. Significant changes in particle size and morphology were observed, and the post-reduction cooling was found to be an important stage in the process. The spark plasma sintering (SPS) parameters were optimized to minimize the grain growth while achieving sufficient densification. Grain sizes in the range of 500 nm to 1 lm, with compaction density of 95-98% were obtained. Preliminary measurements of thermal diffusivity and conductivity showed the dependence on grain size as well as on porosity. TE transport properties were measured in the temperature range of 300-650 K. Sample showed p-type behavior with a positive Seebeck coefficient, which increases with increasing temperature. Electrical conductivity measurements indicate metallic behavior and it decreases with increasing temperature. Thermal conductivity also decreases with increasing temperature and major contribution is due to the lattice component. A TE figure of merit of 0.15 was achieved for high purity CoSb 3 nanostructured TE material at 650 K and these results are comparable with the values reported for the best unfilled/undoped CoSb 3 in the literature.
MRS Proceedings, 2012
ABSTRACTSkutterudites are known to be efficient thermoelectric (TE) materials in the temperature ... more ABSTRACTSkutterudites are known to be efficient thermoelectric (TE) materials in the temperature range from 600 K to 900 K. Dimensionless figure of merit (ZT) for filled skutterudite TE materials have been reported as ca. 1 at 800 K. Novel nano- engineering approaches and filling of the skutterudites crystal can further improve the transport properties and ultimately the ZT. Although classified among the promising TE materials, research on their large-scale production via bottom up synthetic routes is rather limited. In this work, large quantity of cobalt antimonide (CoSb3) based skutterudites nanopowder (NP) was fabricated through a room temperature co-precipitation precursor method. Dried precipitates were process by thermo-chemical treatment steps including calcination (in air) and reduction (in hydrogen). CoSb3 NPs were then mixed with silver (Ag) nanoparticles at different weight percentages (1%, 5% and 10% by wt) to form nanocomposites. Skutterudite NP was then consolidated by...
RSC Advances, 2012
For the preparation of electron conducting material the following chemicals, all from Sigma-Aldri... more For the preparation of electron conducting material the following chemicals, all from Sigma-Aldrich Company were used: 6.75 g of Ce(N0 3) 3 • 6H 2 0 0.75 g of Sm(N0 3) 3 • 6H 2 0 1.25 g of Zn(N0 3) 2 • 6H 2 0 1.00 g of Sr(N0 3) 2 1.575 g of Li 2 CO 3 8.25 g of NiCO 3 •2Ni(OH) 2 • xH 2 O 2.525 g of CuCO 3 • Cu(OH) 2 0.0125g of SrCO 3 Solid state reaction method has been used with one time intermediate grindings at 800 o C for 4 h.
Journal of Materials Science, 2014
Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compounds doped w... more Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compounds doped with various rare-earth elements with high purity and homogeneity, which can be processed under hydrogen into nanostructured oxide-dispersed tungsten composite powders having several potential applications. However, hydrogen reduction of doped tungsten oxide compounds is rather complex, affecting the morphology and composition of the final powder. In this study, we have investigated the reduction of tungstic acid in the presence of Y and we provide the experimental evidence that Y 2 O 3 can be separated from Y-doped tungstic acid via hydrogen reduction to produce Y 2 O 3-W powders. The processed powders were further consolidated by spark plasma sintering at different temperatures and holding times at 75 MPa pressure and characterized. The optimized SPS conditions suggest sintering at 1400°C for 3 min holding time to achieve higher density composites with an optimum finer grain size (3 lm) and a hardness value up to 420 H V. Major grain growth takes place at temperatures above 1300°C during sintering. From the density values obtained, it is recommend to apply higher pressure before 900°C to obtain maximum density. Oxides inclusions present in the matrix were identified as Y 2 O 3 Á3WO 3 and Y 2 O 3 ÁWO 3 during high resolution microscopic investigations.
Physical Review Letters, 2001
Physical Review B, 2006
We investigated the magnetic properties of the system CuTe2O5 by susceptibility and electron spin... more We investigated the magnetic properties of the system CuTe2O5 by susceptibility and electron spin resonance measurements. The anisotropy of the effective g-factors and the ESR linewidth indicates that the anticipated structural dimer does not correspond to the singlet-forming magnetic dimer. Moreover, the spin susceptibility of CuTe2O5 can only be described by taking into account interdimer interactions of the same order of magnitude than the intradimer coupling. Analyzing the exchange couplings in the system we identify the strongest magnetic coupling between two Cu ions to be mediated by super-super exchange interaction via a bridging Te ligand, while the superexchange coupling between the Cu ions of the structural dimer only results in the second strongest coupling.
Physical Review B, 2006
The crystal structure of the copper(II) tellurium(IV) oxochloride Cu4Te5O12Cl4 (Cu-45124) is comp... more The crystal structure of the copper(II) tellurium(IV) oxochloride Cu4Te5O12Cl4 (Cu-45124) is composed of weakly coupled tetrahedral Cu clusters and shows crystallographic similarities with the intensively investigated compound Cu2Te2O5X2, with X = Cl, Br (Cu-2252). It differs from the latter by a larger separation of the tetrahedra within the crystallographic ab plane, that allows a more direct assignment of important inter-tetrahedra exchange paths and the existence of an inversion center. Magnetic susceptibility and specific heat evidence antiferromagnetic, frustrated correlations of the Cu spin moments and long range ordering with Tc=13.6 K. The entropy related to the transition is reduced due to quantum fluctuations. In Raman scattering a well structured low energy magnetic excitation is observed at energies of ≈50K (35cm −1). This energy scale is reduced as compared to Cu-2252.
Journal of Materials Science, 2012
ABSTRACT Recently magnesium silicide (Mg2Si) has received great interest from thermoelectric (TE)... more ABSTRACT Recently magnesium silicide (Mg2Si) has received great interest from thermoelectric (TE) society because of its non-toxicity, environmental friendliness, comparatively high abundance, and low production material cost as compared to other TE systems. It also exhibited promising transport properties, including high electrical conductivity and low thermal conductivity, which improved the overall TE performance (ZT). In this work, Mg2Si powder was obtained through high energy ball milling under inert atmosphere, starting from commercial magnesium silicide pieces (99.99 %, Alfa Aesar). To maintain fine microstructure of the powder, spark plasma sintering (SPS) process has been used for consolidation. The Mg2Si powder was filled in a graphite die to perform SPS and the influence of process parameters as temperature, heating rate, holding time and applied pressure on the microstructure, and densification of compacts were studied in detail. The aim of this study is to optimize SPS consolidation parameters for Mg2Si powder to achieve high density of compacts while maintaining the nanostructure. X-Ray diffraction (XRD) was utilized to investigate the crystalline phase of compacted samples and scanning and transmission electron microscopy (SEM & TEM) coupled with Energy-Dispersive X-ray Analysis (EDX) was used to evaluate the detailed microstructural and chemical composition, respectively. All sintered samples showed compaction density up to 98 %. Temperature dependent TE characteristics of SPS compacted Mg2Si as thermal conductivity, electrical resistivity, and Seebeck coefficient were measured over the temperature range of RT 600 °C for samples processed at 750 °C, reaching a final ZT of 0.14 at 600 °C.
Journal of Materials Chemistry, 2012