Marius Reinecker | University of Vienna (original) (raw)
Papers by Marius Reinecker
Philosophical Magazine Letters, 2011
... Mining is often done in environments containing porous mineral assemblies 1111.Hudson-Edwards... more ... Mining is often done in environments containing porous mineral assemblies 1111.Hudson-Edwards, KA, Schell, C and Macklin, MG. 1999. Appl. Geochem. ... Vives, E,Soto-Parra, D, Manosa, L, Romero, R and Planes, A. 2009. Phys. Rev. ...
Journal of Physics: Condensed Matter, 2012
The elastic and anelastic properties of three different samples of Fe x O have been determined in... more The elastic and anelastic properties of three different samples of Fe x O have been determined in the frequency range 0.1-2 MHz by resonant ultrasound spectroscopy and in the range 0.1-50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T N ∼ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe 4 q, between a symmetry-breaking strain, e 4 , and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C 44 does not go to zero at the critical temperature, T * c , due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear-quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm 2 , and T N > T * c. Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T N and T * c in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.
Applied Physics Letters, 2009
Jerky elasticity was observed by Dynamical Mechanical Analyzer (DMA) measurements in a single cry... more Jerky elasticity was observed by Dynamical Mechanical Analyzer (DMA) measurements in a single crystal of the shape memory alloy Cu 74.08 Al 23.13 Be 2.79. Jerks appear as spikes in the dissipation of the elastic response function and relate to the formation of avalanches during the transformation between the austenite and the martensite phase. The statistics of the avalanches follows the predictions of avalanche criticality P(E)~ E-ε where P(E) is the probability of finding an avalanche with the energy E. This result reproduces, within experimental uncertainties, previous findings by acoustic emission techniques.
Journal of Applied Physics, 2010
Thermal expansion was determined for two series of ternary compounds, Ba 8 M x Ge 46−x and Ba 8 M... more Thermal expansion was determined for two series of ternary compounds, Ba 8 M x Ge 46−x and Ba 8 M x Si 46−x , with M = Cu, Zn, Pd, Ag, Cd, Pt, and Au and for several quaternary compounds for which we investigated the influence of substitution by Zn/Ni in Ba 8 Zn x Ge 46−x as well as the dependence of thermal expansion on the Si/Ge ratio in Ba 8 Cu 5 Si x Ge 41−x. In the temperature range from 4.2 to 300 K the thermal expansion of all ternary compounds was measured with a capacitance dilatometer, whereas from 300 to 700 K for several selected samples a dynamic mechanical analyzer was employed. The low temperature data compare well with the lattice parameters of single crystals, gained from measurements at three different temperatures ͑100, 200, and 300 K͒. For a quantitative description of thermal expansion the semiclassical model of Mukherjee et al. ͓Phys. Rev. Lett. 76, 1876 ͑1996͔͒ was used, which also provided reliable accurate values of the Debye and Einstein temperatures. Results in this respect show good agreement with the corresponding data derived from temperature dependent x-ray diffraction and specific heat measurements. Furthermore the present paper is a comprehensive collection and discussion of all thermal expansion data of intermetallic type-I-clathrate materials so far available in the literature including our results of thermal expansion measurements of the Ge-and Si-based type-I-clathrates listed above.
We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of ... more We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS 2 nanotubes and Mo 6 S 2 I 8 nanowires. The addition of a small amount of nanoparticles (<1 wt-%) leads to an increase of the glass transition temperature T g as compared to the pure elastomeric matrix. A second peak observed in tan in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from-130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above T g. Below T g , this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.
Polymer-Nanopartikel-Komposite (PNCs) spielen eine zunehmende Rolle im technologischen Bereich. D... more Polymer-Nanopartikel-Komposite (PNCs) spielen eine zunehmende Rolle im technologischen Bereich. Die Eigenschaften von Polymeren konnen durch die Zugabe von Nanopartikeln signifikant verandert werden und dies birgt ein groses Potential fur verschiedene Anwendungen. Wie prasentieren DMA Messungen von Polyurea-Elastomeren und auf Polyurea-Elastomeren basierenden Nanokompositen, welche anorganische M oS 2 Nanorohrchen und M o 6 S 2 I 8 Nanodrahte beinhalten. Polyurea ist ein spontan auftretendes PNC und weist eine segregierte Struktur mit in einer im elastischen Sinne weichen Matrix eingebetteten harten Nanodomanen. Zwei verschiedene Peaks konnten in tanδ beobachtet werden – sowohl in reinen Elastomeren als auch bei Elastomer-Nanopartikel-Kompositen. Der erste Peak bei T g1 ist auf einen Glasubergang in der weichen Matrix zuruckzufuhren. Der zweite Peak bei T g2 ist einem Glasubergang in Regionen nahe an den harten Domanen zuzuordnen, welche eine Verlangsamung der Dynamik erfahren. Verg...
ABSTRACT A strong softening of the elastic shear modulus C66 has been observed as one approaches ... more ABSTRACT A strong softening of the elastic shear modulus C66 has been observed as one approaches the spin-density-wave (SDW) transition in Ba122 from high temperature [1,2]. A smaller softening is still observed for superconducting Co-doped Ba122 crystals, followed by distinct hardening below Tc[1,2]. This elastic response has been taken as evidence either for electronic-magnetic nematic fluctuations [1], or as evidence for a structural quantum critical point near optimal doping [2]. Here we study the elastic response of various Fe-based superconductors by a recently developed technique based upon a three-point bending experiment in a high-resolution capacitance dilatometer. We measure the temperature dependence of the Young's modulus, which for thin slabs can be shown to be closely related to C66 for a given orientation. This is confirmed by measurements on Co-doped Ba122, for which we find very similar results as previously reported [1,2]. We will report on new measurements of the Young's modulus on other Fe-based Ba122 systems in order to study the universality of the elastic response at the SDW and superconducting transitions. [1] R. M. Fernandes, et al., Phys. Rev. Lett. 105, 157003 (2010). [2] M. Yoshizawa, et al., J. Phys. Soc. Jpn. 81, 024604 (2012).
Dalton Trans.
Novel filled skutterudites BayNi4Sb12−xSnx (ymax = 0.93) have been prepared and thoroughly charac... more Novel filled skutterudites BayNi4Sb12−xSnx (ymax = 0.93) have been prepared and thoroughly characterized, which show anomalously high lattice thermal conductivity.
Phase Transitions
ABSTRACT Size effects play an important role in structural phase transitions, melting transitions... more ABSTRACT Size effects play an important role in structural phase transitions, melting transitions, in martensitic materials, glass transitions, etc. Very often the question arises, whether a measured size effect originates from the geometrical confinement itself, or if it appears due to the interaction with the limiting surface. Using dynamic mechanical analysis (DMA) technique we have studied various microphase segregated polymers, molecular glass forming liquids and supercooled water confined in nanoporous silica as well as in biological tissues. Here we show on some selected examples that DMA measurements can be used to study relaxation processes in detail and to disentangle in favourable cases pure pore size effects from effects that are induced by the confining surface.
Materials Science and Engineering: B, 2010
Time-of-flight and resonant ultrasound spectroscopy techniques were employed for elastic moduli m... more Time-of-flight and resonant ultrasound spectroscopy techniques were employed for elastic moduli measurements on a set of various Fe4Sb12- and Co4Sb12-based skutterudites filled by mischmetal, didymium, or alkaline earths (Ca, Sr, Ba). A weak temperature influence on the longitudinal modulus C11 indicates weak degradation of elastic properties within the thermoelectric working temperature range. Elastic moduli for Co4Sb12-based skutterudites are only slightly higher than for Fe4Sb12-based skutterudites, and the influence of various filler atoms or filling fractions on the elastic moduli is even smaller. Ball milled and hot pressed samples (grain size ∼250nm) illustrate an obvious improvement of elastic properties in relation to those hot pressed from hand milled powders (grain size ∼50μm). Debye temperatures calculated from sound velocity measurements are comparable to the values obtained from the parameters fitted to thermal expansion, which indicate that Co4Sb12-based skutterudites having slightly higher values than Fe4Sb12-based skutterudites. Vickers hardness is increased by Co or Ni substitution and demonstrates a linear dependence on density, Young's modulus, and shear modulus.
Acta Materialia, 2013
ABSTRACT Using thermoelectricity to directly convert (waste) heat energy into useful electricity ... more ABSTRACT Using thermoelectricity to directly convert (waste) heat energy into useful electricity faces a number of challenges. Not only are optimised thermal and electrical transport properties required resulting in a high figure of merit ZT and a high thermal–electric conversion efficiency η over a wide temperature range, thermoelectric (TE) materials must have sufficient mechanical integrity to survive continuous heating–cooling cycles. Thermal expansion of the material as well as the mechanical properties play an important role, i.e. their values should be as similar as possible for p- and n-type alloys to avoid stresses when used in a TE device. In this paper multiple filled p- and n-type skutterudites (Ba,Sr,DD,Yb)y(Fe1–xNix)4Sb12 with a ZT > 1 and η ≈ 13% are presented, for the first time showing, in contrast to hitherto investigated skutterudites, nearly identical thermal expansion coefficients and elastic moduli. The ZT values of these skutterudites could be further enhanced by more than 20% after severe plastic deformation via high-pressure torsion.
arXiv: Materials Science, 2017
Novel filled skutterudites EpyNi4Sb12-xSnx (Ep = Ba and La) have been prepared by arc melting fol... more Novel filled skutterudites EpyNi4Sb12-xSnx (Ep = Ba and La) have been prepared by arc melting followed by annealing at 250C, 350C and 450C up to 30 days in sealed quartz vials. A maximum filling level of y = 0.93 and y = 0.65 was achieved for the Ba and La filled skutterudite, respectively. Single-phase samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and Ba0.92Ni4Sb6.7Sn5.3 were employed for measurements of the physical properties i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. Resistivity data showed a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from maxima in the Seebeck coefficient data as a function of temperature. Temperature dependent single crystal X-ray structure analyses (at 100 K, 200 K and 300 K) revealed the thermal expansion coefficients, Einstein and Debye temperatures for two selected samples Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data compar...
We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of ... more We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS2 nanotubes and Mo 6 S 2 I 8 nanowires. The addition of a small amount of nanoparticles (<1 wt-%) leads to an increase of the glass transition temperature T g as compared to the pure elastomeric matrix. A second peak observed in tan in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from -130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above T g . Below T g , this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.
physica status solidi (a), 2013
The properties of polymers can be significantly changed by incorporating nanoparticles, which yie... more The properties of polymers can be significantly changed by incorporating nanoparticles, which yields a great potential for applications. In the present study, we use nanocomposites of new polyurea elastomers filled with 0.1, 0.5, and 1 wt.% MoS 2 nanotubes. Using dynamic mechanical analysis (DMA) measurements we show, that the glass transition temperatures
Physical Review Letters, 2014
The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x... more The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x))2As2 iron-based superconductors is obtained from measurements of the elastic shear modulus using a three-point bending setup in a capacitance dilatometer. Nematic fluctuations, although weakened by doping, extend over the whole superconducting dome in both systems, suggesting their close tie to superconductivity. Evidence for quantum critical behavior of χφ is, surprisingly, only found for Ba(Fe(1-x)Co(x))2As2 and not for Ba(1-x)K(x)Fe2As2--the system with the higher maximal Tc value.
Journal of Alloys and Compounds, 2012
Journal of Physics-condensed Matter, 2012
The elastic and anelastic properties of three different samples of Fe x O have been determined in... more The elastic and anelastic properties of three different samples of Fe x O have been determined in the frequency range 0.1-2 MHz by resonant ultrasound spectroscopy and in the range 0.1-50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T N ∼ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe 4 q, between a symmetry-breaking strain, e 4 , and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C 44 does not go to zero at the critical temperature, T * c , due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear-quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm 2 , and T N > T * c . Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T N and T * c in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.
Philosophical Magazine Letters, 2011
... Mining is often done in environments containing porous mineral assemblies 1111.Hudson-Edwards... more ... Mining is often done in environments containing porous mineral assemblies 1111.Hudson-Edwards, KA, Schell, C and Macklin, MG. 1999. Appl. Geochem. ... Vives, E,Soto-Parra, D, Manosa, L, Romero, R and Planes, A. 2009. Phys. Rev. ...
Journal of Physics: Condensed Matter, 2012
The elastic and anelastic properties of three different samples of Fe x O have been determined in... more The elastic and anelastic properties of three different samples of Fe x O have been determined in the frequency range 0.1-2 MHz by resonant ultrasound spectroscopy and in the range 0.1-50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T N ∼ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe 4 q, between a symmetry-breaking strain, e 4 , and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C 44 does not go to zero at the critical temperature, T * c , due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear-quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm 2 , and T N > T * c. Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T N and T * c in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.
Applied Physics Letters, 2009
Jerky elasticity was observed by Dynamical Mechanical Analyzer (DMA) measurements in a single cry... more Jerky elasticity was observed by Dynamical Mechanical Analyzer (DMA) measurements in a single crystal of the shape memory alloy Cu 74.08 Al 23.13 Be 2.79. Jerks appear as spikes in the dissipation of the elastic response function and relate to the formation of avalanches during the transformation between the austenite and the martensite phase. The statistics of the avalanches follows the predictions of avalanche criticality P(E)~ E-ε where P(E) is the probability of finding an avalanche with the energy E. This result reproduces, within experimental uncertainties, previous findings by acoustic emission techniques.
Journal of Applied Physics, 2010
Thermal expansion was determined for two series of ternary compounds, Ba 8 M x Ge 46−x and Ba 8 M... more Thermal expansion was determined for two series of ternary compounds, Ba 8 M x Ge 46−x and Ba 8 M x Si 46−x , with M = Cu, Zn, Pd, Ag, Cd, Pt, and Au and for several quaternary compounds for which we investigated the influence of substitution by Zn/Ni in Ba 8 Zn x Ge 46−x as well as the dependence of thermal expansion on the Si/Ge ratio in Ba 8 Cu 5 Si x Ge 41−x. In the temperature range from 4.2 to 300 K the thermal expansion of all ternary compounds was measured with a capacitance dilatometer, whereas from 300 to 700 K for several selected samples a dynamic mechanical analyzer was employed. The low temperature data compare well with the lattice parameters of single crystals, gained from measurements at three different temperatures ͑100, 200, and 300 K͒. For a quantitative description of thermal expansion the semiclassical model of Mukherjee et al. ͓Phys. Rev. Lett. 76, 1876 ͑1996͔͒ was used, which also provided reliable accurate values of the Debye and Einstein temperatures. Results in this respect show good agreement with the corresponding data derived from temperature dependent x-ray diffraction and specific heat measurements. Furthermore the present paper is a comprehensive collection and discussion of all thermal expansion data of intermetallic type-I-clathrate materials so far available in the literature including our results of thermal expansion measurements of the Ge-and Si-based type-I-clathrates listed above.
We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of ... more We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS 2 nanotubes and Mo 6 S 2 I 8 nanowires. The addition of a small amount of nanoparticles (<1 wt-%) leads to an increase of the glass transition temperature T g as compared to the pure elastomeric matrix. A second peak observed in tan in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from-130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above T g. Below T g , this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.
Polymer-Nanopartikel-Komposite (PNCs) spielen eine zunehmende Rolle im technologischen Bereich. D... more Polymer-Nanopartikel-Komposite (PNCs) spielen eine zunehmende Rolle im technologischen Bereich. Die Eigenschaften von Polymeren konnen durch die Zugabe von Nanopartikeln signifikant verandert werden und dies birgt ein groses Potential fur verschiedene Anwendungen. Wie prasentieren DMA Messungen von Polyurea-Elastomeren und auf Polyurea-Elastomeren basierenden Nanokompositen, welche anorganische M oS 2 Nanorohrchen und M o 6 S 2 I 8 Nanodrahte beinhalten. Polyurea ist ein spontan auftretendes PNC und weist eine segregierte Struktur mit in einer im elastischen Sinne weichen Matrix eingebetteten harten Nanodomanen. Zwei verschiedene Peaks konnten in tanδ beobachtet werden – sowohl in reinen Elastomeren als auch bei Elastomer-Nanopartikel-Kompositen. Der erste Peak bei T g1 ist auf einen Glasubergang in der weichen Matrix zuruckzufuhren. Der zweite Peak bei T g2 ist einem Glasubergang in Regionen nahe an den harten Domanen zuzuordnen, welche eine Verlangsamung der Dynamik erfahren. Verg...
ABSTRACT A strong softening of the elastic shear modulus C66 has been observed as one approaches ... more ABSTRACT A strong softening of the elastic shear modulus C66 has been observed as one approaches the spin-density-wave (SDW) transition in Ba122 from high temperature [1,2]. A smaller softening is still observed for superconducting Co-doped Ba122 crystals, followed by distinct hardening below Tc[1,2]. This elastic response has been taken as evidence either for electronic-magnetic nematic fluctuations [1], or as evidence for a structural quantum critical point near optimal doping [2]. Here we study the elastic response of various Fe-based superconductors by a recently developed technique based upon a three-point bending experiment in a high-resolution capacitance dilatometer. We measure the temperature dependence of the Young's modulus, which for thin slabs can be shown to be closely related to C66 for a given orientation. This is confirmed by measurements on Co-doped Ba122, for which we find very similar results as previously reported [1,2]. We will report on new measurements of the Young's modulus on other Fe-based Ba122 systems in order to study the universality of the elastic response at the SDW and superconducting transitions. [1] R. M. Fernandes, et al., Phys. Rev. Lett. 105, 157003 (2010). [2] M. Yoshizawa, et al., J. Phys. Soc. Jpn. 81, 024604 (2012).
Dalton Trans.
Novel filled skutterudites BayNi4Sb12−xSnx (ymax = 0.93) have been prepared and thoroughly charac... more Novel filled skutterudites BayNi4Sb12−xSnx (ymax = 0.93) have been prepared and thoroughly characterized, which show anomalously high lattice thermal conductivity.
Phase Transitions
ABSTRACT Size effects play an important role in structural phase transitions, melting transitions... more ABSTRACT Size effects play an important role in structural phase transitions, melting transitions, in martensitic materials, glass transitions, etc. Very often the question arises, whether a measured size effect originates from the geometrical confinement itself, or if it appears due to the interaction with the limiting surface. Using dynamic mechanical analysis (DMA) technique we have studied various microphase segregated polymers, molecular glass forming liquids and supercooled water confined in nanoporous silica as well as in biological tissues. Here we show on some selected examples that DMA measurements can be used to study relaxation processes in detail and to disentangle in favourable cases pure pore size effects from effects that are induced by the confining surface.
Materials Science and Engineering: B, 2010
Time-of-flight and resonant ultrasound spectroscopy techniques were employed for elastic moduli m... more Time-of-flight and resonant ultrasound spectroscopy techniques were employed for elastic moduli measurements on a set of various Fe4Sb12- and Co4Sb12-based skutterudites filled by mischmetal, didymium, or alkaline earths (Ca, Sr, Ba). A weak temperature influence on the longitudinal modulus C11 indicates weak degradation of elastic properties within the thermoelectric working temperature range. Elastic moduli for Co4Sb12-based skutterudites are only slightly higher than for Fe4Sb12-based skutterudites, and the influence of various filler atoms or filling fractions on the elastic moduli is even smaller. Ball milled and hot pressed samples (grain size ∼250nm) illustrate an obvious improvement of elastic properties in relation to those hot pressed from hand milled powders (grain size ∼50μm). Debye temperatures calculated from sound velocity measurements are comparable to the values obtained from the parameters fitted to thermal expansion, which indicate that Co4Sb12-based skutterudites having slightly higher values than Fe4Sb12-based skutterudites. Vickers hardness is increased by Co or Ni substitution and demonstrates a linear dependence on density, Young's modulus, and shear modulus.
Acta Materialia, 2013
ABSTRACT Using thermoelectricity to directly convert (waste) heat energy into useful electricity ... more ABSTRACT Using thermoelectricity to directly convert (waste) heat energy into useful electricity faces a number of challenges. Not only are optimised thermal and electrical transport properties required resulting in a high figure of merit ZT and a high thermal–electric conversion efficiency η over a wide temperature range, thermoelectric (TE) materials must have sufficient mechanical integrity to survive continuous heating–cooling cycles. Thermal expansion of the material as well as the mechanical properties play an important role, i.e. their values should be as similar as possible for p- and n-type alloys to avoid stresses when used in a TE device. In this paper multiple filled p- and n-type skutterudites (Ba,Sr,DD,Yb)y(Fe1–xNix)4Sb12 with a ZT > 1 and η ≈ 13% are presented, for the first time showing, in contrast to hitherto investigated skutterudites, nearly identical thermal expansion coefficients and elastic moduli. The ZT values of these skutterudites could be further enhanced by more than 20% after severe plastic deformation via high-pressure torsion.
arXiv: Materials Science, 2017
Novel filled skutterudites EpyNi4Sb12-xSnx (Ep = Ba and La) have been prepared by arc melting fol... more Novel filled skutterudites EpyNi4Sb12-xSnx (Ep = Ba and La) have been prepared by arc melting followed by annealing at 250C, 350C and 450C up to 30 days in sealed quartz vials. A maximum filling level of y = 0.93 and y = 0.65 was achieved for the Ba and La filled skutterudite, respectively. Single-phase samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and Ba0.92Ni4Sb6.7Sn5.3 were employed for measurements of the physical properties i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. Resistivity data showed a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from maxima in the Seebeck coefficient data as a function of temperature. Temperature dependent single crystal X-ray structure analyses (at 100 K, 200 K and 300 K) revealed the thermal expansion coefficients, Einstein and Debye temperatures for two selected samples Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data compar...
We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of ... more We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS2 nanotubes and Mo 6 S 2 I 8 nanowires. The addition of a small amount of nanoparticles (<1 wt-%) leads to an increase of the glass transition temperature T g as compared to the pure elastomeric matrix. A second peak observed in tan in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from -130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above T g . Below T g , this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.
physica status solidi (a), 2013
The properties of polymers can be significantly changed by incorporating nanoparticles, which yie... more The properties of polymers can be significantly changed by incorporating nanoparticles, which yields a great potential for applications. In the present study, we use nanocomposites of new polyurea elastomers filled with 0.1, 0.5, and 1 wt.% MoS 2 nanotubes. Using dynamic mechanical analysis (DMA) measurements we show, that the glass transition temperatures
Physical Review Letters, 2014
The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x... more The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x))2As2 iron-based superconductors is obtained from measurements of the elastic shear modulus using a three-point bending setup in a capacitance dilatometer. Nematic fluctuations, although weakened by doping, extend over the whole superconducting dome in both systems, suggesting their close tie to superconductivity. Evidence for quantum critical behavior of χφ is, surprisingly, only found for Ba(Fe(1-x)Co(x))2As2 and not for Ba(1-x)K(x)Fe2As2--the system with the higher maximal Tc value.
Journal of Alloys and Compounds, 2012
Journal of Physics-condensed Matter, 2012
The elastic and anelastic properties of three different samples of Fe x O have been determined in... more The elastic and anelastic properties of three different samples of Fe x O have been determined in the frequency range 0.1-2 MHz by resonant ultrasound spectroscopy and in the range 0.1-50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T N ∼ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe 4 q, between a symmetry-breaking strain, e 4 , and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C 44 does not go to zero at the critical temperature, T * c , due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear-quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm 2 , and T N > T * c . Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T N and T * c in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.