arXiv subjects

Mohamed Zbiri

Publications and source records attributed to Mohamed Zbiri.

At least 19 recordsLinked to original sources

arXiv2026

Tuning Separator Chemistry: Improving Zn Anode Compatibility via Functionalized Chitin Nanofibers

Aqueous zinc (Zn) batteries (AZBs) face significant challenges due to the limited compatibility of Zn anodes with conventional separators, leading to dendrite growth, hydrogen evolution reaction (HER), and poor cycling stability. While separator design is crucial for optimizing battery performance, its potential remains underexplored. The commonly used glass fiber (GF) filters were not originally designed as battery separators. To address their limitations, nanochitin derived from waste shrimp shells was used to fabricate separators with varying concentrations of amine and carboxylic functional groups. This study investigates how the type and concentration of these groups influence the separator's properties and performance. In a mild acidic electrolyte that protonates the amine groups, the results showed that the density of both ammonium and carboxylic groups in the separators significantly affected water structure and ionic conductivity. Quasi-Elastic Neutron Scattering (QENS) revealed that low-functionalized chitin, particularly with only ammonium groups, promotes strongly bound water with restricted mobility, thereby enhancing Zn plating and stripping kinetics. These separators exhibit exceptional Zn stability over 2000 hours at low current densities (0.5 mA/cm2), maintaining low overpotentials and stable polarization. Additionally, the full cell consisting of Zn||NaV3O8.1.5H2O showed a cycle life of over 2000 cycles at 2 A/g, demonstrating the compatibility of the nanochitin-based separators with low concentrations of functional surface groups. These results demonstrate the importance of a simple separator design for improving the overall performance of AZBs.

cond-mat.mtrl-sci↗

arXiv2024

Dynamics of Polyalkylfluorene Conjugated Polymers: Insights from Neutron Spectroscopy and Molecular Dynamics Simulations

The dynamics of the conjugated polymers poly(9,9-dioctylfluorene) (PF8) and poly(9,9-didodecylfluorene) (PF12), differing by the length of their side chains, is investigated in the amorphous phase using the quasielastic neutron scattering (QENS) technique. The measurements are synergistically underpinned by molecular dynamics (MD) simulations. The probe is focused on the picosecond time scale, where the structural dynamics of both PF8 and PF12 would mainly be dominated by motions of their side chains. The measurements highlighted temperature-induced dynamics, reflected in the broadening of the QENS spectra upon heating. The MD simulations reproduced well the observations; hence validating the MD force fields, the adopted amorphous model structures, and the numerical procedure. As the QENS spectra are dominated by the signal from the hydrogens on the backbones and side chains of PF8 and PF12, extensive analysis of the MD simulations allowed: (i) tagging these hydrogens, (ii) estimating their contributions to the self-part of the van Hove functions and hence to the QENS spectra, and (iii) determining the activation energies of the different motions involving the tagged hydrogens. PF12 is found to exhibit QENS spectra broader than those of PF8, indicating a more pronounced motion of the didodecyl chains of PF12 as compared to dioctyl chains of PF8. This is in agreement with the outcome of our MD analysis: (i) confirming a lower glass transition temperature of PF12 compared to PF8, (ii) showing PF12 having a lower density than PF8, and (iii) highlighting lower activation energies of the motions of PF12 in comparison with PF8. This study helped to gain insights into the temperature-induced side-chain dynamics of the PF8 and PF12 conjugated polymers, influencing their stability, which could potentially impact the performance of the associated optoelectronic active layer.

cond-mat.soft↗

arXiv2022

Structural Dynamics of Polymer:Non-Fullerene Organic Solar Cell Blends: A Neutron Spectroscopy Perspective

Organic solar cells (OSCs) based on ADA-type (acceptor-donor-acceptor) non-fullerene acceptors (NFAs) exhibit improved power conversion efficiency (PCE) compared to the conventional fullerene-based analogues. The optoelectronic properties of OSC active layer blends are correlated to their underlying structural dynamics and therefore influence the device performance. Using synergistically different neutron spectroscopy techniques, we studied the dynamics of binary and ternary blends made of the NFAs O-IDTBR and O-IDFBR and the regioregular donor polymer P3HT. Deuteration was considered for a contrast variation purpose. In addition to shedding light on the miscibilty and alloying characters of the blends, a main outcome of this work is the evidenced similar dynamical response of the blend components. This finding is in contrast with our previous neutron spectroscopy and molecular dynamics studies of the fullerene-based blend P3HT:PCBM, where we highlighted distinct behaviors of P3HT and PCBM in terms of the vitrification/frustration of P3HT and the plasticization of PCBM by P3HT upon blending. Alike P3HT vitrification is not presently observed. The absence or the weak vitrification evidenced here is in line with recent reports and is likely related to the improved PCE exhibited by the ADA-type NFA-based OSCs.

cond-mat.mtrl-sci↗

arXiv2021

Quantitative insights into the phase behaviour and miscibility of organic photovoltaic active layers from the perspective of neutron spectroscopy

We present a neutron spectroscopy based method to study quantitatively the partial miscibility and phase behaviour of an organic photovoltaic active layer made of conjugated polymer:small molecule blends, presently illustrated with the regio-random poly(3-hexylthiophene-2,5-diyl) and fullerene [6,6]-Phenyl C$_{61}$ butyric acid methyl ester (RRa-P3HT:PCBM) system. We perform both inelastic neutron scattering and quasi-elastic neutron scattering measurements to study the structural dynamics of blends of different compositions enabling us to resolve the phase behaviour. The difference of neutron cross sections between RRa-P3HT and PCBM, and the use of deuteration technique, offer a unique opportunity to probe the miscibility limit of fullerene in the amorphous polymer-rich phase and to tune the contrast between the polymer and the fullerene phases, respectively. Therefore, the proposed approach should be universal and relevant to study new non-fullerene acceptors that are closely related - in terms of chemical structures - to the polymer, where other conventional imaging and spectroscopic techniques present a poor contrast between the blend components.

cond-mat.mtrl-sci↗

arXiv2021

Analysis of external and internal disorder to understand band-like transport in n-type organic semiconductors

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both internal and external (i.e. related to the interactions with the dielectric layer), especially for n-type materials. Internal dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (< a-few-hundred cm-1), which renders it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be external, being controlled by the gate insulator dielectric properties. Here we report on a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory and simulations. We provide unambiguous evidence that ad hoc molecular design enables to free the electron charge carriers from both internal and external disorder to ultimately reach band-like electron transport.

cond-mat.mtrl-sci↗

arXiv2021

Effect of substituting non-polar chains with polar chains on the structural dynamics of small organic molecule and polymer semiconductors

The processability and optoelectronic properties of organic semiconductors can be tuned and manipulated via chemical design. The substitution of the alkyl side chains by oligoethers has recently been successful for applications such as bioelectronic sensors and photocatalytic water-splitting. The carbon-oxygen bond in oligoethers is likely to render the system softer and more prone to dynamical disorder that can be detrimental to charge transport for example. We use neutron spectroscopy, X-Ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized optical microscopy to study the effect of the substitution of n-hexyl (Hex) by triethylene glycol (TEG) on the structural dynamics of two organic semiconductors: a phenylene-bithiophene-phenylene (PTTP) molecule and a fluorene-co-dibenzothiophene (FS) polymer. Counterintuitively, inelastic neutron scattering (INS) reveals a softening of the modes of PTTP and FS with Hex side chains, pointing towards an increased dynamical disorder in these systems. However, T-dependent X-Ray and neutron diffraction, INS and DSC evidence an extra reversible transition close to room temperature (RT) for PTTP with TEG side chains. The observed transition, not accompanied by a change in birefringence, can also be observed by quasi-elastic neutron scattering. A fastening of the TEG side chains dynamics is observed in the case of PTTP and not FS. We therefore assign this transition to the melt of the TEG side chains which are promoting dynamical order at RT, but if crystallising, may introduce an extra reversible structural transition above RT leading to thermal instabilities. A deeper understanding of side chain polarity and structural dynamics can help guide materials design and navigate the intricate balance between electronic charge transport and aqueous swelling, sought for a number of emerging organic electronic and bioelectronic applications.

cond-mat.mtrl-sci↗

arXiv2021

Probing dynamics of water mass transfer in organic porous photocatalyst water-splitting materials by neutron spectroscopy

The quest for efficient and economically accessible cleaner methods to develop sustainable carbon-free energy sources induced a keen interest in the production of hydrogen fuel. This can be achieved via the water-splitting process exploiting solar energy but requiring the use of adequate photocatalysts. Covalent triazine-based frameworks (CTFs) are target photocatalysts for water-splitting. Both electronic and structural characteristics of CTFs, optical bandgaps and porosity, are directly relevant for water-splitting. These can be engineered through chemical design. Porosity can be beneficial to water-splitting by providing larger surface area for the catalytic reactions. However, porosity can also affect both charge transport within the photocatalyst and mass transfer of both reactants and products, thus impacting the overall kinetics of the reaction. We focus on the link between chemical design and water (reactants) mass transfer, playing a key role in the water uptake process and the subsequent hydrogen generation. We use neutron spectroscopy to study water mass transfer in two porous CTFs, CTF-CN and CTF-2, that differ in the polarity of their struts. Quasi-elastic neutron scattering (QENS) is used to quantify the amount of bound water and the translational diffusion of water. Inelastic neutron scattering measurements complement QENS and provides insights into the softness of the CTF structures and the changes in librational degrees of freedom of water in CTFs. We show that CTF-CN exhibits smaller surface area and water uptake due to a softer structure than CTF-2. The current study leads to new insights into the structure-dynamics-property relationship of CTF photo-catalysts that pave the road for a better understanding of the guest-host interaction at the basis of water splitting applications.

cond-mat.mtrl-sci↗

arXiv2021

Impact of chemical structure on the dynamics of mass transfer of water in conjugated microporous polymers: A neutron spectroscopy study

Hydrogen fuel can contribute as a masterpiece in conceiving a robust carbon-free economic puzzle if cleaner methods to produce hydrogen become technically efficient and economically viable. Organic photocatalytic materials such as conjugated microporous materials (CMPs) are potential attractive candidates for water splitting as their energy levels and optical bandgap as well as porosity are tunable through chemical synthesis. The performances of CMPs depend also on the mass transfer of reactants, intermediates and products. Here, we study the mass transfer of water (H2O and D2O), and of triethylamine used as a hole scavenger for hydrogen evolution, by means of neutron spectroscopy. We find that the stiffness of the nodes of the CMPs is correlated with an increase in trapped water, reflected by motions too slow to be quantified by quasi-elastic neutron scattering (QENS). Our study highlights that the addition of the polar sulfone group results in additional interactions between water and the CMP, as evidenced by inelastic neutron scattering (INS), leading to changes in the translational diffusion of water, as determined from the QENS measurements. No changes in triethylamine motions could be observed within CMPs from the present investigations.

cond-mat.mtrl-sci↗

arXiv2019

Anomalous thermal expansion in one-dimensional transition-metal cyanides: Behavior of the trimetallic cyanide Cu$_{1/3}$Ag$_{1/3}$Au$_{1/3}$CN

The structural dynamics of a 1D mixed-metal cyanide, Cu$_{1/3}$Ag$_{1/3}$Au$_{1/3}$CN, with intriguing thermal properties is explored. All the current known related compounds with straight-chain structures, such as CuCN, AgCN, AuCN and M$_x$M'$_{1-x}$CN (M, M' = Cu, Ag, Au), exhibit 1D negative thermal expansion (NTE) along the chains and positive thermal expansion (PTE) perpendicular to them. Cu$_{1/3}$Ag$_{1/3}$Au$_{1/3}$CN exhibits similar PTE perpendicular to the chains, however PTE, rather than NTE, is also observed along the chains. In order to understand the origin of this unexpected behavior, inelastic neutron scattering (INS) measurements were carried out, underpinned by DFT calculations. Synchrotron-based PDF analysis and 13C SSNMR measurements were also performed to build an input structural model for the lattice dynamical study. The results indicate that transverse motions of the metal ions are responsible for the PTE perpendicular to the chains, as is the case for the related group 11 cyanides. However NTE along the chain due to the tension effect of these transverse motions is not observed. For this system, DFT-based phonon calculations predict small PTE along the chain due to low-energy chain-slipping modes induced by a bond-rotation effect on the weak metallophilic bonds. However the observed PTE is greater than that predicted with the straight-chain model. Small bends in the chain to accommodate truly co-planar metals provide an alternative explanation for thermal behavior. These would mitigate the tension effect induced by the transverse motions of the metals and, as temperature increases and the chains move further apart, a straightening could occur resulting in the observed PTE. This hypothesis is further supported by unusual evolution in the phonon spectra, which suggest small changes in local symmetry with temperature.

cond-mat.mtrl-sci↗

arXiv2019

Phonon dynamics in the layered negative thermal expansion compounds Cu$_x$Ni$_{2-x}$(CN)$_4$

This study explores the relationship between phonon dynamics and negative thermal expansion (NTE) in Cu$_x$Ni$_{2-x}$(CN)$_4$. The partial replacement of nickel (II) by copper (II) in Ni(CN)$_2$ leads to a line phase, CuNi(CN)$_4$ (x = 1), and a solid solution, Cu$_x$Ni$_{2-x}$(CN)$_4$ (0 $\leq$ x $\leq$ 0.5). CuNi(CN)$_4$ adopts a layered structure related to that of Ni(CN)$_2$ (x = 0), and interestingly exhibits 2D NTE which is about 1.5 times larger. Inelastic neutron scattering (INS) measurements combined with first principles lattice dynamical calculations provide insights into the effect of Cu$^{2+}$ on the underlying mechanisms behind the anomalous thermal behavior in all the Cu$_x$Ni$_{2-x}$(CN)$_4$ compounds. The solid solutions are presently reported to also show 2D NTE. The INS results highlight that as the Cu$^{2+}$ content increases in Cu$_x$Ni$_{2-x}$(CN)$_4$, large shifts to lower energies are observed in modes consisting of localized in- and out-of-plane librational motions of the CN ligand, which contribute to the NTE in CuNi(CN)$_4$. Mode Grüneisen parameters calculated for CuNi(CN)$_4$ show that acoustic and low-energy optic modes contribute the most to the NTE, as previously shown in Ni(CN)$_2$. However, mode eigenvectors reveal a large deformation of the [CuN4] units compared to the [NiC4] units, resulting in phonon modes not found in Ni(CN)$_2$, whose NTE-driving phonons consist predominately of rigid-unit modes. The deformations in CuNi(CN)$_4$ arise because the d$^9$ square-planar center is easier to deform than the d$^8$ one, resulting in a greater range of out-of-plane motions for the adjoining ligands.

cond-mat.mtrl-sci↗

arXiv2019

Freeing electrons from extrinsic and intrinsic disorder yields band-like transport in n-type organic semiconductors

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both intrinsic and extrinsic, especially for n-type materials. Intrinsic dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (< a-few-hundred cm-1), which renders it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be extrinsic, being controlled by the gate insulator dielectric properties. Here we report on a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory and simulations. We provide unambiguous evidence that ad hoc molecular design enables to free the electron charge carriers from both intrinsic and extrinsic disorder to ultimately reach band-like electron transport.

cond-mat.mtrl-sci↗

arXiv2019

Phonons and Anomalous Lattice Behaviour in KMnAg3(CN)6 and KNiAu3(CN)6: Inelastic Neutron Scattering and First-Principles Calculations

Cyanide based framework compounds are known to show large negative thermal expansion behaviour. Here we report the phonon and anomalous lattice behavior of two metal cyanide framework compounds i.e. KMnAg3(CN)6 and KNiAu3(CN)6. We have studied the role of van der Waals dispersion and magnetic interactions on structural stability of these compounds. The behavior of these compounds under isotropic compression shows the presence of negative linear compressibility. The calculated phonon spectra, validated by inelastic neutron scattering measurements and elastic constants are used to study the negative thermal expansion behavior which is found to arise from low energy phonon modes involving the folding of A-NC-B-CN-A linkage about B atoms.

cond-mat.mtrl-sci↗

arXiv2019

Lattice dynamics and negative thermal expansion in the framework compound ZnNi(CN)$_4$ with two-dimensional and three-dimensional local environments

ZnNi(CN)$_4$ is a 3D framework material consisting of two interpenetrating PtS-type networks in which tetrahedral [ZnN$_4$] units are linked by square-planar [NiC$_4$] units. Both the parent compounds, cubic Zn(CN)$_2$ and layered Ni(CN)$_2$, are known to exhibit 3D and 2D negative thermal expansion (NTE), respectively. Temperature-dependent inelastic neutron scattering measurements were performed on a powdered sample of ZnNi(CN)$_4$ to probe phonon dynamics. The measurements were underpinned by ab initio lattice dynamical calculations. Good agreement was found between the measured and calculated generalized phonon density-of-states, validating our theoretical model and indicating that it is a good representation of the dynamics of the structural units. The calculated linear thermal expansion coefficients are $α_a$=-21.2 $\times$ 10$^{-6}$ K$^{-1}$ and $α_c$=+14.6$\times$10$^{-6}$K$^{-1}$, leading to an overall volume expansion coefficient $α_V$ of -26.95$\times$10$^{-6}$K$^{-1}$, pointing towards pronounced NTE behavior. Analysis of the derived mode-Grüneisen parameters shows that optic modes around 12 and 40 meV make a significant contribution to NTE. These modes involve localized rotational motions of the [NiC$_4$] and/or [ZnN$_4$] rigid units, echoing what has previously been observed in Zn(CN)$_2$ and Ni(CN)$_2$. However, in ZnNi(CN)$_4$, modes below 10 meV have the most negative Grüneisen parameters. Analysis of their eigenvectors reveals that a large transverse motion of the Ni atom in the direction perpendicular to its square-planar environment induces a distortion of the units. This mode is a consequence of the Ni atom being constrained only in 2D within a 3D framework. Hence, although rigid-unit modes account for some of the NTE-driving phonons, the added d-o-f compared with Zn(CN)$_2$ results in modes with twisting motions, capable of inducing greater NTE.

cond-mat.mtrl-sci↗

arXiv2017

Phonon Spectra in the Parent Superconducting Iron-tuned Telluride Fe$_{1+x}$Te from Inelastic Neutron Scattering and Ab Initio Calculations

We report inelastic neutron scattering measurements of phonon spectra in the parent superconductor iron-tuned chalcogenide Fe$_{1+x}$Te, for two different x contents (x $\leq$ 0.11), using neutron time-of-flight technique. Thermal neutron spectroscopy allowed to collect the low-temperature Stokes spectra over an extended Q-range, at 2, 40 and 120K - hence covering both the magnetic monoclinic and the paramagnetic tetragonal phases. Whereas cold-neutrons allowed to measure high-resolution anti-Stokes spectra at 140, 220 and 300K, thus covering the tetragonal phase. Our results evidence a spin-phonon coupling behaviour towards the observed noticeable temperature-dependent change of the Stokes spectra across the transition temperatures. On the other hand, the anti-Stokes spectra reveal a pronounced hardening of the low-energy, acoustic region, of the phonon spectrum, upon heating, indicating a strong anharmonicity and a subtle dependence of phonons on structural evolution within the tetragonal phase. Experimental results are accompanied by ab initio calculations of phonon spectra of the tetragonal stoichiometric phase for a comparison with the high-resolution anti-Stokes spectra. Calculations included different density functional methods. Spin polarization and van der Waals interaction, were either considered or neglected, individually or concomitantly, in order to study their respective effect on lattice dynamics description. Our results suggest that including van der Waals interaction has only a slight effect on phonon dynamics, however, phonon spectra are better described when spin polarization is included, in a cooperative way with van der Waals interactions.

cond-mat.mtrl-sci↗

arXiv2017

Ultrafast Molecular Transport on Carbon Surfaces: The Diffusion of Ammonia on Graphite

We present a combined experimental and theoretical study of the self-diffusion of ammonia on exfoliated graphite. Using neutron time-of-flight spectroscopy we are able to resolve the ultrafast diffusion process of adsorbed ammonia, NH$_3$, on graphite. Together with van der Waals corrected density functional theory calculations we show that the diffusion of NH$_3$ follows a hopping motion on a weakly corrugated potential energy surface with an activation energy of about 4 meV which is particularly low for this type of diffusive motion. The hopping motion includes further a significant number of long jumps and the diffusion constant of ammonia adsorbed on graphite is determined with $D=3.9 \cdot 10^{-8}~\mbox{m}^2 /\mbox{s}$ at 94 K.

cond-mat.mtrl-sci↗

arXiv2017

Anomalous Thermal Expansion, Negative Linear Compressibility and High-Pressure Phase Transition in ZnAu2(CN)4: Neutron Inelastic Scattering and Lattice Dynamics Studies

We present temperature dependent inelastic neutron scattering measurments, accompanied byab-initio calculations of phonon spectra and elastic properties as a function of pressure to understand anharmonicity of phonons and to study the mechanism of negative thermal expansion and negative linear compressibility behaviour of ZnAu2(CN)4. The mechanism is identified in terms of specific anharmonic modes that involve bending of the Zn(CN)4-Au- Zn(CN)4 linkage. The high-pressure phase transition at about 2 GPa is also investigated and found to be related to softening of a phonon mode at the L-point at the Brillouin zone boundary and its coupling with a zone-centre phonon and an M-point phonon in the ambient pressure phase. Although the phase transition is primarily driven by a L-point soft phonon mode, which usually leads to a second order transition with a 2 x 2 x 2 supercell, in the present case the structure is close to an elastic instability that leads to a weakly first order transition.

cond-mat.mtrl-sci↗

arXiv2017

Absence of magnetism in the superconductor Ba2Ti2Fe2As4O: Insights from inelastic neutron scattering measurements and ab initio calculations of phonon spectra

Ba2Ti2Fe2As4O is a self-doped superconductor exhibiting a Tc ~ 21.5 K and containing, distinctively with respect to other Fe-based superconductors, not only [Fe2As2] layers but also conducting [Ti2O] sheets. This compound exhibits a transition at T* ~ 125 K which has tentatively been assigned in the literature to a possible density-wave order. However, the nature of this density wave (whether it is a charge- or spin-induced) is still under debate. Magnetism in Ba2Ti2Fe2As4O has never been experimentally confirmed, which raises the question whether this superconductor might be non-magnetic or exhibiting a very weak magnetism. Here, we report evidence from inelastic neutron scattering (INS) measurements and ab initio calculations of phonon spectra pointing towards absence of magnetism in Ba2Ti2Fe2As4O. The INS measurements did not reveal any noticeable change of the phonon spectra across Tc, neither could magnetic effects be observed within the accessible (Q, E) space, setting Ba2Ti2Fe2As4O as an unconventional superconductor. The effect of magnetism on describing phonon spectra was further investigated by performing ab initio calculations. In this context, non-magnetic calculations reproduced well the measured phonon spectra. Therefore, our results indicate a non-magnetic and unconventional character of the superconductor Ba2Ti2Fe2As4O.

cond-mat.mtrl-sci↗

arXiv2016

Determination of the vibrational contribution to the entropy change at the martensitic transformation in Ni-Mn-Sn metamagnetic shape memory alloys: A combined approach of time-of-flight neutron spectroscopy and ab-initio calculations

The different contributions to the entropy change linked to the austenite-martensitic transition in a Ni-Mn-Sn metamagnetic shape memory alloy have been determined by combining different experimental techniques. The vibrational contribution has been inferred from the vibrational density of states of both the martensitic and austenite phases. This has been accomplished by combining time-of-flight neutron scattering measurements and ab-initio calculations. Further, the electronic part of the entropy change has also been calculated. Since the martensitic transformation takes place between two paramagnetic phases, the magnetic contribution can be neglected and the entropy change can be reduced to the sum of two terms: vibrational and electronic. The obtained value of the vibrational contribution (-36 \pm 5 J kg^(-1) K^(-1)) nearly provides the total entropy change measured by calorimetry (-41 \pm 3 J kg^(-1) K^(-1)), the difference being the electronic contribution within the experimental error.

cond-mat.mtrl-sci↗