Stéphane Gorsse | CNRS & University of Bordeaux (original) (raw)

Papers by Stéphane Gorsse

Journal of Applied Physics, 2011

The series of glassy ribbons Gd 60 M 30 In 10 (M ¼ Mn, Co, Ni, Cu) was synthesized by melt-spinni... more The series of glassy ribbons Gd 60 M 30 In 10 (M ¼ Mn, Co, Ni, Cu) was synthesized by melt-spinning. The change of transition element M in these Gd-based metallic glasses was proven to induce huge variations of the Curie temperature T C , magnetic entropy change peak values DS m peak , and widths at half maximum values of the magnetic entropy change dT. When M is non magnetic (M ¼ Co, Ni, Cu), the samples behave similarly: they display high values of DS m peak (between-6.6 and-8.2 J/kg K in a magnetic field variation of 4.6 T), average dT values (between 77 and 120 K) and no magnetic hysteresis. On the contrary, when M carries a magnetic moment (M ¼ Mn), some irreversibility appears at low temperature, DS m peak is lower (only 3.1 J/kg K for l 0 H ¼ 4.6 T) and the magnetic transition is very large (dT ¼ 199 K for l 0 H ¼ 4.6 T). These features are explained by some antiparallel coupling between Mn atoms randomly located in the metallic glass. This leads to the occurrence of a cluster-glass behavior at low temperature (35 K), following the ferromagnetic transition observed at 180 K when the temperature is decreased. Also, power law fittings of DS m peak and dT versus l 0 H were performed and show that dT is less field dependent than DS m peak. We could then identify an interesting way of improving the refrigeration capacity of the material at low magnetic field. V

Philosophical Magazine Letters, 2006

It has been known for some time that trace additions (<∼0.1 at.%) of s... more It has been known for some time that trace additions (<∼0.1 at.%) of selected elements to some age-hardenable alloys can have a disproportionate effect on the hardening response. This is now known to be related to the formation of heterogeneities (clusters or precipitates) on the matrix lattice at which the nucleation of hardening precipitates may be enhanced leading to a


Aspergillus niger is one of the most important microorganisms used in biotechnology sector. This ... more Aspergillus niger is one of the most important microorganisms used in biotechnology sector. This species is able to produce naphtho-gamma-pyrones (NγPs), which have excellent antioxidant activity. In the present study, spores and NγPs production has been investigated through solid state fermentation (SSF) of A. niger on different agricultural by-products which, from an economical perspective, constitute cheaper substrates than the synthetic ones, in addition of being more eco-friendly. An optimized NγP yields of 8,12 mg/g dry matter was obtained after 10 days of SSF at 27°C using a mix of sugarcane bagasse, wheat bran and potatoes flour (50/30/20 (w/w/w) respectively. Cultures were carried out in ORSTOM bioreactor using Raimbault glass columns (diameter: 4cm, length: 20cm) packed with 3g solids. Initial moisture content was 75% with an initial aeration rate of 60 ml/min of saturated humid. A significant positive correlation between ergosterol – specific sterol produced by fungi and ...

Materials Chemistry and Physics, 2021

Abstract Polycrystalline Ni0.05Mo3Sb5.4Te1.6 thermoelectric (TE) material samples were mixed with... more Abstract Polycrystalline Ni0.05Mo3Sb5.4Te1.6 thermoelectric (TE) material samples were mixed with NiSb nanoparticles (60 – 80 nm) in 0, 0.034, 0.074 and 0.16 volume fractions, then hot-pressed and their TE transport properties were characterized. There was a gradual increase in electrical conductivity with the addition of NiSb nanoparticles. The electrical conductivity (σ) of the 0.16 sample was increased by 163% compared to the NiSb-free sample. Except for the 0.16 sample, all samples showed alloy scattering (σ ∼ T–0.5). With an increase in NiSb content, the Fermi energy appeared to be reduced, getting closer to the valence band edge. For all samples, the variation in lattice thermal conductivity with temperature (κl ∼ T–0.27) was very similar, indicating that the mode of phonon scattering was the same in all samples.

Journal of Alloys and Compounds, 2020

While ordered L1 2 or gamma prime precipitates in face centered cubic (FCC) based microstructures... more While ordered L1 2 or gamma prime precipitates in face centered cubic (FCC) based microstructures have been extensively used for strengthening nickel or cobalt base superalloys, and more recently in high entropy alloys (HEAs) or complex concentrated alloys (CCAs), the possibility of exploiting ordered B2 precipitates in FCC-based systems has been relatively less investigated. The present study shows the propensity of developing a heterogeneous microstructure, consisting of two different distributions of FCC grain sizes, and two different size scales of B2 precipitates, within an FCC-based Al 0.5 Co 1.5 CrFeNi 1.5 HEA/ CCA. This alloy composition has been designed using solution thermodynamics-based modeling such that it has a high phase fraction and solvus temperature of the B2 phase. The resulting heterogenous microstructure exhibited an approximately 400% increase in yield strength with respect to the singlephase FCC solid solution condition of the same alloy while maintaining very good tensile ductility~20%.

Scripta Materialia, 2020

In the context of cast alloy development for high temperature applications, high entropy superall... more In the context of cast alloy development for high temperature applications, high entropy superalloys (HESA) have exhibited superior cost specific tensile strength than that of superalloys such as CM247LC. Compositions of HESA are distinctively different from those of cast superalloys with higher contents of Fe and Ti, making HESA cheaper and lighter. Comparing to superalloys, although HESA has adopted the template of FCC-structured () matrix and coherent L1 2-structured () precipitates,  is enriched with solutes with higher intrinsic strength, rendering positive lattice misfit, and the high entropy  matrix may have attributed a good combination of strength and ductility.

Scientific Reports, 2020

This paper reports a novel eutectoid nano-lamellar (FCC + L12)/(BCC + B2) microstructure that has... more This paper reports a novel eutectoid nano-lamellar (FCC + L12)/(BCC + B2) microstructure that has been discovered in a relatively simple Al0.3CoFeNi high entropy alloy (HEA) or complex concentrated alloy (CCA). This novel eutectoid nano-lamellar microstructure presumably results from the complex interplay between Al-mediated lattice distortion (due to its larger atomic radius) in a face-centered cubic (FCC) CoFeNi solid solution, and a chemical ordering tendency leading to precipitation of ordered phases such as L12 and B2. This eutectoid microstructure is a result of solid-state decomposition of the FCC matrix and therefore distinct from the commonly reported eutectic microstructure in HEAs which results from solidification. This novel nano-lamellar microstructure exhibits a tensile yield strength of 1074 MPa with a reasonable ductility of 8%. The same alloy can be tuned to form a more damage-tolerant FCC + B2 microstructure, retaining high tensile yield stress (~900 MPa) with appr...

Acta Materialia, 2018

Twinning is a key deformation mechanism in face-centered-cubic (fcc)-based and some body-centered... more Twinning is a key deformation mechanism in face-centered-cubic (fcc)-based and some body-centeredcubic (bcc)-based alloys, which imparts excellent strength-ductility combination by increasing strainhardenability. Typically, twinning in fcc-based alloys increases when the stacking fault energy is lowered via changes in composition. The present study clearly demonstrates that deformation twinning can be enhanced when hard-intermetallic compounds like ordered B2 and sigma phases form in the fcc matrix of a high entropy alloy (HEA), leading to an excellent combination of strength, ductility, and strain-hardenability. Such a combination of properties was achieved by exploiting the novel and often unusual phase stability regimes that can be accessed in these complex concentrated HEAs. The present study exploits a unique three-phase mixture of recrystallized fine-grained fcc þ B2 þ sigma in a prototypical Al 0.3 CoCrFeNi HEA to demonstrate this effect. Coupling transmission electron microscopy and molecular dynamics simulations revealed that B2 grains enhance deformation twinning by raising the local stress levels, consequently forming substantially thicker twins as compared to the single fcc-phase condition of Al 0.3 CoCrFeNi. The local stresses were further accommodated via nano-twinning, limited B2 plasticity, and highly restricted micro-cracks in and around the sigma grains.

Acta Materialia, 2018

Often the experimentally-observed, single-phase high entropy alloy (HEA) is the result of second-... more Often the experimentally-observed, single-phase high entropy alloy (HEA) is the result of second-phase precipitation constrained by thermodynamic and kinetic factors. Using Al 0.3 CoCrFeNi as a candidate HEA, this paper demonstrates the strong influence of thermomechanical processing on the transformation pathway adopted for isothermal second-phase precipitation. A traditional thermo-mechanical processing route comprised of homogenization cold-rolling solution treatment in the single fcc phase region, followed by a precipitation anneal at a lower temperature, results in a homogeneous distribution of nanometer scale-ordered L1 2 (gamma prime-like) precipitates within the fcc matrix. In contrast, if cold-rolling is followed directly by annealing at the precipitation temperature, then the resulting microstructural evolution pathway changes completely, with concurrent recrystallization of the matrix fcc grains and precipitation of B2 and sigma phases, largely at the grain boundaries. These experimentally observed variations in transformation pathway have been rationalized via the competition between the thermodynamic driving force and activation barrier for second-phase nucleation in this alloy, coupled with the kinetics of the process. The microstructural variations that result from these dramatically different phase transformation pathways can lead to some rather exceptional mechanical properties that can be varied over a large range even for a single Al 0.3 CoCrFeNi HEA composition.

Materials Science Forum, 2010

ABSTRACT A physically-based model is proposed for the competitive precipitation of multiple phase... more ABSTRACT A physically-based model is proposed for the competitive precipitation of multiple phases (bcc-Fe, Fe 3 B, Nd 2 Fe 14 B, Nd 2 Fe 23 B 3 , NdFe 4 B 4 and Fe 2 B) from an amorphous Fe-B-Nd matrix. These materials form the basis of a class of nanocomposite hard magnets. The nucleation and growth of the different phases are calculated using computational thermodynamics and kinetics tools with input from a thermodynamic assessment of this system. In some alloy compositions, the phase formation sequence during crystallization shows significant sensitivity to the heating-rate. Model calculations illustrate that this effect cannot be explained by homogeneous nucleation and growth of the phases. The possible role of heterogeneous nucleation is briefly discussed.

Physical Review B, 2006

A thermodynamic analysis of the onset driving force for crystallization of super-cooled liquid ha... more A thermodynamic analysis of the onset driving force for crystallization of super-cooled liquid has been conducted to explain strong composition dependency of the glass forming ability in the Ca-Mg-Zn ternary alloy system observed experimentally. In addition to the onset driving force, other energetic and kinetic factors are discussed to explain the observed glass stabilities. The universality of this method is discussed, thus establishing an analytic approach for determining the most stable glass in a given alloy system.

Journal of Solid State Chemistry, 2011

Gd 5 CoSi 2 was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffractio... more Gd 5 CoSi 2 was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffraction shows that the ternary silicide crystallizes in a tetragonal structure deriving from the Cr 5 B 3-type (I4/mcm space group; a=7.5799(4) and c=13.5091(12) Å as unit cell parameters). The Rietveld refinement shows a mixed occupancy on the (8h) site between Si and Co atoms. Magnetization and specific heat measurements performed on Gd 5 CoSi 2 reveal a ferromagnetic behaviour below T C =168 K. This magnetic ordering is associated to an interesting magnetocaloric effect; the adiabatic temperature change ΔT ad is about 3.1 and 5.9 K, respectively, for a magnetic field change of 2 and 4.6 T.

Journal of Materials Science, 2013

CrSi and Cr 1-x Fe x Si particles embedded in a CrSi 2 matrix have been prepared by hot pressing ... more CrSi and Cr 1-x Fe x Si particles embedded in a CrSi 2 matrix have been prepared by hot pressing from CrSi 1.9 , CrSi 2 , and CrSi 2.1 powders produced by ball milling using either WC or stainless steel milling media. The samples were characterized by powder X-ray diffraction, scanning, and transmission electron microscopy and electron microprobe analysis. The final crystallite size of CrSi 2 obtained from the XRD patterns is about 40 and 80 nm for SS-and WC-milled powders, respectively, whereas the size of the second phase inclusions in the hot pressed samples is about 1-5 lm. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, and figure of merit (ZT) were analyzed in the temperature range from 300 to 800 K. While the ball-milling process results in a lower electrical resistivity and thermal conductivity due to the presence of the inclusions and the refinement of the matrix microstructure, respectively, the Seebeck coefficient is negatively affected by the formation of the inclusions which leads to a modest improvement of ZT.

Journal of Materials Science, 2012

CrSi 2 was earlier reported to be an interesting thermoelectric material for high temperature app... more CrSi 2 was earlier reported to be an interesting thermoelectric material for high temperature applications because of its high oxidation resistance and good mechanical properties. In order to enhance its figure of merit, Mn at Cr site and Al at Si site were substituted into CrSi 2. Our results indicate that Cr 1-x Mn x Si 2-x Al x solid solutions exhibit significantly lower thermal conductivity and a higher figure of merit than CrSi 2 .

Journal of Alloys and Compounds, 2008

Ce2Ni2Ga has been prepared in both amorphous and crystallized form. The first one has been obtain... more Ce2Ni2Ga has been prepared in both amorphous and crystallized form. The first one has been obtained by melt-spinning process. Electrical resistivity, magnetic susceptibility, heat capacity and Seebeck coefficient measurements have been carried out on these two forms. A valence transition from intermediate valence (IV) behavior (crystallized) to a trivalent (Ce3+) behavior (amorphous) of the cerium have been pointed out in

Chemistry of Materials, 2008

The synthesis of materials were carried out as described in refs. (1) and (2), i.e., by heating o... more The synthesis of materials were carried out as described in refs. (1) and (2), i.e., by heating of the simple oxides (Cu 2 O, MoO 3 and WO 3) at 700°C for 24 hours. As-prepared sample were found to be single phased (form). Powder X-ray diffraction was performed using a Bruker D8 diffractometer, equipped with a germanium monochromator (Cu-K-L 3 , =1.540598Å) and a VÅNTEC ® position sensitive detector. The sample, a powder filled in a Plexiglas cavity, was leveled tangential to the

Chemistry of Materials, 2012

Journal of Applied Physics, 2011

The series of glassy ribbons Gd 60 M 30 In 10 (M ¼ Mn, Co, Ni, Cu) was synthesized by melt-spinni... more The series of glassy ribbons Gd 60 M 30 In 10 (M ¼ Mn, Co, Ni, Cu) was synthesized by melt-spinning. The change of transition element M in these Gd-based metallic glasses was proven to induce huge variations of the Curie temperature T C , magnetic entropy change peak values DS m peak , and widths at half maximum values of the magnetic entropy change dT. When M is non magnetic (M ¼ Co, Ni, Cu), the samples behave similarly: they display high values of DS m peak (between-6.6 and-8.2 J/kg K in a magnetic field variation of 4.6 T), average dT values (between 77 and 120 K) and no magnetic hysteresis. On the contrary, when M carries a magnetic moment (M ¼ Mn), some irreversibility appears at low temperature, DS m peak is lower (only 3.1 J/kg K for l 0 H ¼ 4.6 T) and the magnetic transition is very large (dT ¼ 199 K for l 0 H ¼ 4.6 T). These features are explained by some antiparallel coupling between Mn atoms randomly located in the metallic glass. This leads to the occurrence of a cluster-glass behavior at low temperature (35 K), following the ferromagnetic transition observed at 180 K when the temperature is decreased. Also, power law fittings of DS m peak and dT versus l 0 H were performed and show that dT is less field dependent than DS m peak. We could then identify an interesting way of improving the refrigeration capacity of the material at low magnetic field. V

Philosophical Magazine Letters, 2006

It has been known for some time that trace additions (<∼0.1 at.%) of s... more It has been known for some time that trace additions (<∼0.1 at.%) of selected elements to some age-hardenable alloys can have a disproportionate effect on the hardening response. This is now known to be related to the formation of heterogeneities (clusters or precipitates) on the matrix lattice at which the nucleation of hardening precipitates may be enhanced leading to a


Aspergillus niger is one of the most important microorganisms used in biotechnology sector. This ... more Aspergillus niger is one of the most important microorganisms used in biotechnology sector. This species is able to produce naphtho-gamma-pyrones (NγPs), which have excellent antioxidant activity. In the present study, spores and NγPs production has been investigated through solid state fermentation (SSF) of A. niger on different agricultural by-products which, from an economical perspective, constitute cheaper substrates than the synthetic ones, in addition of being more eco-friendly. An optimized NγP yields of 8,12 mg/g dry matter was obtained after 10 days of SSF at 27°C using a mix of sugarcane bagasse, wheat bran and potatoes flour (50/30/20 (w/w/w) respectively. Cultures were carried out in ORSTOM bioreactor using Raimbault glass columns (diameter: 4cm, length: 20cm) packed with 3g solids. Initial moisture content was 75% with an initial aeration rate of 60 ml/min of saturated humid. A significant positive correlation between ergosterol – specific sterol produced by fungi and ...

Materials Chemistry and Physics, 2021

Abstract Polycrystalline Ni0.05Mo3Sb5.4Te1.6 thermoelectric (TE) material samples were mixed with... more Abstract Polycrystalline Ni0.05Mo3Sb5.4Te1.6 thermoelectric (TE) material samples were mixed with NiSb nanoparticles (60 – 80 nm) in 0, 0.034, 0.074 and 0.16 volume fractions, then hot-pressed and their TE transport properties were characterized. There was a gradual increase in electrical conductivity with the addition of NiSb nanoparticles. The electrical conductivity (σ) of the 0.16 sample was increased by 163% compared to the NiSb-free sample. Except for the 0.16 sample, all samples showed alloy scattering (σ ∼ T–0.5). With an increase in NiSb content, the Fermi energy appeared to be reduced, getting closer to the valence band edge. For all samples, the variation in lattice thermal conductivity with temperature (κl ∼ T–0.27) was very similar, indicating that the mode of phonon scattering was the same in all samples.

Journal of Alloys and Compounds, 2020

While ordered L1 2 or gamma prime precipitates in face centered cubic (FCC) based microstructures... more While ordered L1 2 or gamma prime precipitates in face centered cubic (FCC) based microstructures have been extensively used for strengthening nickel or cobalt base superalloys, and more recently in high entropy alloys (HEAs) or complex concentrated alloys (CCAs), the possibility of exploiting ordered B2 precipitates in FCC-based systems has been relatively less investigated. The present study shows the propensity of developing a heterogeneous microstructure, consisting of two different distributions of FCC grain sizes, and two different size scales of B2 precipitates, within an FCC-based Al 0.5 Co 1.5 CrFeNi 1.5 HEA/ CCA. This alloy composition has been designed using solution thermodynamics-based modeling such that it has a high phase fraction and solvus temperature of the B2 phase. The resulting heterogenous microstructure exhibited an approximately 400% increase in yield strength with respect to the singlephase FCC solid solution condition of the same alloy while maintaining very good tensile ductility~20%.

Scripta Materialia, 2020

In the context of cast alloy development for high temperature applications, high entropy superall... more In the context of cast alloy development for high temperature applications, high entropy superalloys (HESA) have exhibited superior cost specific tensile strength than that of superalloys such as CM247LC. Compositions of HESA are distinctively different from those of cast superalloys with higher contents of Fe and Ti, making HESA cheaper and lighter. Comparing to superalloys, although HESA has adopted the template of FCC-structured () matrix and coherent L1 2-structured () precipitates,  is enriched with solutes with higher intrinsic strength, rendering positive lattice misfit, and the high entropy  matrix may have attributed a good combination of strength and ductility.

Scientific Reports, 2020

This paper reports a novel eutectoid nano-lamellar (FCC + L12)/(BCC + B2) microstructure that has... more This paper reports a novel eutectoid nano-lamellar (FCC + L12)/(BCC + B2) microstructure that has been discovered in a relatively simple Al0.3CoFeNi high entropy alloy (HEA) or complex concentrated alloy (CCA). This novel eutectoid nano-lamellar microstructure presumably results from the complex interplay between Al-mediated lattice distortion (due to its larger atomic radius) in a face-centered cubic (FCC) CoFeNi solid solution, and a chemical ordering tendency leading to precipitation of ordered phases such as L12 and B2. This eutectoid microstructure is a result of solid-state decomposition of the FCC matrix and therefore distinct from the commonly reported eutectic microstructure in HEAs which results from solidification. This novel nano-lamellar microstructure exhibits a tensile yield strength of 1074 MPa with a reasonable ductility of 8%. The same alloy can be tuned to form a more damage-tolerant FCC + B2 microstructure, retaining high tensile yield stress (~900 MPa) with appr...

Acta Materialia, 2018

Twinning is a key deformation mechanism in face-centered-cubic (fcc)-based and some body-centered... more Twinning is a key deformation mechanism in face-centered-cubic (fcc)-based and some body-centeredcubic (bcc)-based alloys, which imparts excellent strength-ductility combination by increasing strainhardenability. Typically, twinning in fcc-based alloys increases when the stacking fault energy is lowered via changes in composition. The present study clearly demonstrates that deformation twinning can be enhanced when hard-intermetallic compounds like ordered B2 and sigma phases form in the fcc matrix of a high entropy alloy (HEA), leading to an excellent combination of strength, ductility, and strain-hardenability. Such a combination of properties was achieved by exploiting the novel and often unusual phase stability regimes that can be accessed in these complex concentrated HEAs. The present study exploits a unique three-phase mixture of recrystallized fine-grained fcc þ B2 þ sigma in a prototypical Al 0.3 CoCrFeNi HEA to demonstrate this effect. Coupling transmission electron microscopy and molecular dynamics simulations revealed that B2 grains enhance deformation twinning by raising the local stress levels, consequently forming substantially thicker twins as compared to the single fcc-phase condition of Al 0.3 CoCrFeNi. The local stresses were further accommodated via nano-twinning, limited B2 plasticity, and highly restricted micro-cracks in and around the sigma grains.

Acta Materialia, 2018

Often the experimentally-observed, single-phase high entropy alloy (HEA) is the result of second-... more Often the experimentally-observed, single-phase high entropy alloy (HEA) is the result of second-phase precipitation constrained by thermodynamic and kinetic factors. Using Al 0.3 CoCrFeNi as a candidate HEA, this paper demonstrates the strong influence of thermomechanical processing on the transformation pathway adopted for isothermal second-phase precipitation. A traditional thermo-mechanical processing route comprised of homogenization cold-rolling solution treatment in the single fcc phase region, followed by a precipitation anneal at a lower temperature, results in a homogeneous distribution of nanometer scale-ordered L1 2 (gamma prime-like) precipitates within the fcc matrix. In contrast, if cold-rolling is followed directly by annealing at the precipitation temperature, then the resulting microstructural evolution pathway changes completely, with concurrent recrystallization of the matrix fcc grains and precipitation of B2 and sigma phases, largely at the grain boundaries. These experimentally observed variations in transformation pathway have been rationalized via the competition between the thermodynamic driving force and activation barrier for second-phase nucleation in this alloy, coupled with the kinetics of the process. The microstructural variations that result from these dramatically different phase transformation pathways can lead to some rather exceptional mechanical properties that can be varied over a large range even for a single Al 0.3 CoCrFeNi HEA composition.

Materials Science Forum, 2010

ABSTRACT A physically-based model is proposed for the competitive precipitation of multiple phase... more ABSTRACT A physically-based model is proposed for the competitive precipitation of multiple phases (bcc-Fe, Fe 3 B, Nd 2 Fe 14 B, Nd 2 Fe 23 B 3 , NdFe 4 B 4 and Fe 2 B) from an amorphous Fe-B-Nd matrix. These materials form the basis of a class of nanocomposite hard magnets. The nucleation and growth of the different phases are calculated using computational thermodynamics and kinetics tools with input from a thermodynamic assessment of this system. In some alloy compositions, the phase formation sequence during crystallization shows significant sensitivity to the heating-rate. Model calculations illustrate that this effect cannot be explained by homogeneous nucleation and growth of the phases. The possible role of heterogeneous nucleation is briefly discussed.

Physical Review B, 2006

A thermodynamic analysis of the onset driving force for crystallization of super-cooled liquid ha... more A thermodynamic analysis of the onset driving force for crystallization of super-cooled liquid has been conducted to explain strong composition dependency of the glass forming ability in the Ca-Mg-Zn ternary alloy system observed experimentally. In addition to the onset driving force, other energetic and kinetic factors are discussed to explain the observed glass stabilities. The universality of this method is discussed, thus establishing an analytic approach for determining the most stable glass in a given alloy system.

Journal of Solid State Chemistry, 2011

Gd 5 CoSi 2 was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffractio... more Gd 5 CoSi 2 was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffraction shows that the ternary silicide crystallizes in a tetragonal structure deriving from the Cr 5 B 3-type (I4/mcm space group; a=7.5799(4) and c=13.5091(12) Å as unit cell parameters). The Rietveld refinement shows a mixed occupancy on the (8h) site between Si and Co atoms. Magnetization and specific heat measurements performed on Gd 5 CoSi 2 reveal a ferromagnetic behaviour below T C =168 K. This magnetic ordering is associated to an interesting magnetocaloric effect; the adiabatic temperature change ΔT ad is about 3.1 and 5.9 K, respectively, for a magnetic field change of 2 and 4.6 T.

Journal of Materials Science, 2013

CrSi and Cr 1-x Fe x Si particles embedded in a CrSi 2 matrix have been prepared by hot pressing ... more CrSi and Cr 1-x Fe x Si particles embedded in a CrSi 2 matrix have been prepared by hot pressing from CrSi 1.9 , CrSi 2 , and CrSi 2.1 powders produced by ball milling using either WC or stainless steel milling media. The samples were characterized by powder X-ray diffraction, scanning, and transmission electron microscopy and electron microprobe analysis. The final crystallite size of CrSi 2 obtained from the XRD patterns is about 40 and 80 nm for SS-and WC-milled powders, respectively, whereas the size of the second phase inclusions in the hot pressed samples is about 1-5 lm. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, and figure of merit (ZT) were analyzed in the temperature range from 300 to 800 K. While the ball-milling process results in a lower electrical resistivity and thermal conductivity due to the presence of the inclusions and the refinement of the matrix microstructure, respectively, the Seebeck coefficient is negatively affected by the formation of the inclusions which leads to a modest improvement of ZT.

Journal of Materials Science, 2012

CrSi 2 was earlier reported to be an interesting thermoelectric material for high temperature app... more CrSi 2 was earlier reported to be an interesting thermoelectric material for high temperature applications because of its high oxidation resistance and good mechanical properties. In order to enhance its figure of merit, Mn at Cr site and Al at Si site were substituted into CrSi 2. Our results indicate that Cr 1-x Mn x Si 2-x Al x solid solutions exhibit significantly lower thermal conductivity and a higher figure of merit than CrSi 2 .

Journal of Alloys and Compounds, 2008

Ce2Ni2Ga has been prepared in both amorphous and crystallized form. The first one has been obtain... more Ce2Ni2Ga has been prepared in both amorphous and crystallized form. The first one has been obtained by melt-spinning process. Electrical resistivity, magnetic susceptibility, heat capacity and Seebeck coefficient measurements have been carried out on these two forms. A valence transition from intermediate valence (IV) behavior (crystallized) to a trivalent (Ce3+) behavior (amorphous) of the cerium have been pointed out in

Chemistry of Materials, 2008

The synthesis of materials were carried out as described in refs. (1) and (2), i.e., by heating o... more The synthesis of materials were carried out as described in refs. (1) and (2), i.e., by heating of the simple oxides (Cu 2 O, MoO 3 and WO 3) at 700°C for 24 hours. As-prepared sample were found to be single phased (form). Powder X-ray diffraction was performed using a Bruker D8 diffractometer, equipped with a germanium monochromator (Cu-K-L 3 , =1.540598Å) and a VÅNTEC ® position sensitive detector. The sample, a powder filled in a Plexiglas cavity, was leveled tangential to the

Chemistry of Materials, 2012