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| Naji, M. |
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| Motta, Antonella |
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| Aletan, Dirar |
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| Mohamed, Tarek |
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| Ertürk, Emre |
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| Taccardi, Nicola |
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| Kononenko, Denys |
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| Petrov, R. H. | Madrid |
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| Alshaaer, Mazen | Brussels |
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| Bih, L. |
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| Casati, R. |
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| Muller, Hermance |
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| Kočí, Jan | Prague |
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| Šuljagić, Marija |
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| Kalteremidou, Kalliopi-Artemi | Brussels |
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| Azam, Siraj |
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| Ospanova, Alyiya |
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| Blanpain, Bart |
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| Ali, M. A. |
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| Popa, V. |
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| Rančić, M. |
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| Ollier, Nadège |
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| Azevedo, Nuno Monteiro |
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| Landes, Michael |
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| Rignanese, Gian-Marco |
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Walker, David
University of Warwick
in Cooperation with on an Cooperation-Score of 37%
Topics
Publications (17/17 displayed)
- 2024Untangling free carrier and exciton dynamics in layered hybrid perovskites using ultrafast optical and terahertz spectroscopycitations
- 2023Untangling free carrier and exciton dynamics in layered hybrid perovskites using ultrafast optical and terahertz spectroscopycitations
- 2023Operando X-ray and Post-mortem Investigations of Electrochemical Degradation in Single-crystalline LiNi0.8Mn0.1Co0.1O2–Graphite pouch cellscitations
- 2023Tetragonal Kondo Insulator EuCd2Sb2 Discovered via High Pressure High Temperature Synthesiscitations
- 2023Quantifying electrochemical degradation in single-crystalline LiNi0.8Mn0.1Co0.1O2–graphite pouch cells through operando X-ray and post-mortem investigations
- 2023Data for Influence of co-reactants on surface passivation by nanoscale hafnium oxide layers grown by atomic layer deposition on siliconcitations
- 2023Hafnium oxide : a thin film dielectric with controllable etch resistance for semiconductor device fabricationcitations
- 2020Ambient and high pressure CuNiSb₂citations
- 2019Advanced steam measurement techniques: a study of how electrical capacitance measurements are affected by the spatial positioning of water within wet steam
- 2018MnFe0.5Ru0.5O3: An Above-Room-Temperature Antiferromagnetic Semiconductorcitations
- 2018Synthesizing bijective lensescitations
- 2018Cs1−xRbxSnI3 light harvesting semiconductors for perovskite photovoltaicscitations
- 2018Cs 1-: X Rb x SnI 3 light harvesting semiconductors for perovskite photovoltaicscitations
- 2015Thermal, compositional, and compressional demagnetization of cementitecitations
- 2015Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1−xFex)nO3n+1−δ Ruddlesden-Popper superstructurescitations
- 2013Thin film LaYbO3 capacitive structures grown by pulsed laser depositioncitations
- 2001Synthesis and thermal decomposition of tetragonal RbClO4 and volume of fluid O2 from 2 to 9 GPacitations
Places of action
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article
Thermal, compositional, and compressional demagnetization of cementite
Abstract
<p>The 1 bar Curie temperature, T<sub>C</sub>, at which cementite (anthropogenic form of the mineral cohenite, nominally Fe<sub>3</sub>C) abruptly loses ferromagnetism, is found to be sensitive to small deviations from the stoichiometric cementite composition. Stoichiometric Fe<sub>3</sub>C begins to lose magnetic susceptibility at 187 °C. The T<sub>C</sub> of ferromagnetic loss in cementite falls by about 13-14 °C, in either compositional direction, to the limits at either Fe-saturation or graphite-saturation. Formation of C vacancies in, or C stuffings into, Fe<sub>3</sub>C produces non-stoichiometry, disrupts and weakens the Fe magnetic ordering, and produces excess configurational entropy that is proportional to the disruption magnitude. C-excess (∼0.6 at% C) at graphite-saturation is less than the C-deficiency at Fe-saturation (∼2.6 at% C), so the rate at which Curie T<sub>C</sub> drops with cementite C% variation is asymmetric about the stoichiometric composition, being steeper on the C-excess side. This asymmetry reflects the higher excess configurational entropy (and consequently greater weakening of Fe magnetic ordering) generated by C excesses than by C vacancies. The application of ∼6 GPa pressure to stoichiometric Fe<sub>3</sub>C leads to a drop in T<sub>C</sub>, of more than 160 °C, to below room T. This large drop in T<sub>C</sub> with pressure is shown by loss of ferromagnetism in a specimen compressed in a multi-anvil device at room T. Densely sampled synchrotron XRD cell volumes through the transition pressure interval at room T show that there is also a small drop in compressibility near 6 GPa for non-stoichiometric cementites. C-rich cementite retains its magnetism to ∼1 GPa higher P than C-poor cementite. The drop in T<sub>C</sub> with pressure for stoichiometric cementite was tracked in an externally heated diamond-anvil cell by the jump in thermal expansion experienced when cementite loses its magnetostriction above T<sub>C</sub> (Wood et al. 2004; Litasov et al. 2013). T<sub>C</sub> drops parabolically with pressure, as do the Invar alloys (Leger et al. 1972; Winterrose et al. 2009). Both high T and P favor the magnetically disordered (Curie) paramagnetic over the ferromagnetic form of cementite. The observed large positive change in thermal expansion and small negative change in compressibility at the T<sub>C</sub> transition give a good quantitative account of the negative dT<sub>C</sub>/dP slope mapped by the ferro-paramagnetic phase stability boundary through Ehrenfest's (1933) second relation. Our observations of cementite demagnetization at P∼6 GPa, room T confirm the synchrotron Mössbauer work of Gao et al. (2008). The demagnetization pressures based upon experiment are lower than those estimated from existing theoretical treatments by about an order of magnitude. Stability calculations for carbide in the mantle and core are influenced by the choice among ferromagnetic, paramagnetic, and non-magnetic equations of state. Because the ferromagnetic phase is more compressible, the calculated P-T range for cementite stability would be too large under the assumption of ferromagnetism persisting to higher pressures than shown here experimentally. Our results diminish the theoretical P-T range of cementite stability.</p>