Effects of site-occupation disorder on the low-temperature thermal conductivity of molecular crystals

Кривчиков, А. И.; Vdovichenko, G. A.; Korolyuk, O. A.; Bermejo, Francisco Javier; Pardo, Luis Carlos; Tamarit, J. Ll.; Jeżowski, A.; Szewczyk, Daria

doi:10.1016/j.jnoncrysol.2014.08.006

Cited by 13 publications

(10 citation statements)

References 73 publications

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“…Although the occupational disorder should be absent in the reference case of tetrachloromethane, CCl 4 51-53 , the same dynamics has been strikingly revealed by NQR measurements 41 and molecular dynamics simulation 50 . On the other hand, thermal conductivity measurements 54 in the same three halomethane crystals have shown an absence of the characteristic glassy anomalies at moderately low temperatures. The thermal conductivity of these molecular crystals was found to display two distinct temperature regions, the boundary of which roughly coincided with the abovementioned glasslike transitions.…”

Section: Introductionmentioning

confidence: 85%

Emergence of glassy features in halomethane crystals

et al. 2019

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Both structural glasses and disordered crystals are known to exhibit anomalous thermal, vibrational and acoustic properties at low temperatures or low energies, what is still a matter of lively debate. To shed light on this issue, we have studied the halomethane family CBrnCl4−n (n = 0, 1, 2) at low temperature where, despite being perfectly translationally-ordered stable monoclinic crystals, glassy dynamical features had been reported from experiments and molecular dynamics simulations. For n = 1, 2 dynamic disorder originates by the random occupancy of the same lattice sites by either Cl or Br atoms, but not for the ideal reference case of CCl4. Measurements of the low-temperature specific heat (Cp) for all these materials are here reported, which provide evidence of the presence of a broad peak in Debye-reduced Cp(T )/T 3 and in the reduced density of states (g(ω)/ω 2 ) determined by means of neutron spectroscopy, as well as a linear term in Cp usually ascribed in glasses to two-level systems in addition to the cubic term expected for a fully-ordered crystal. Being CCl4 a fully-ordered crystal, we have also performed density functional theory (DFT) calculations, which provide unprecedented detailed information about the microscopic nature of vibrations responsible for that broad peak, much alike the "boson peak" of glasses, finding it to essentially arise from a piling up (at around 3 − 4 meV) of low-energy optical modes together with acoustic modes near the Brillouin-zone limits.

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Section: Introductionmentioning

confidence: 85%

Emergence of glassy features in halomethane crystals

et al. 2019

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“…As a source of entropy, materials undergoing order-disorder transitions have been attracted particular interest because the increase in the number of accessible configurations from N 2 to N 1 occurring across the transition contributes to a specific entropy change RM −1 log(N 1 /N 2 ), that in some cases may reach very large values. Unfortunately, dynamic disorder usually goes against thermal conductivity [32] and density, so it seems hard to foresee an ideal material gathering all the aforementioned properties at the same time. Therefore, a trade-off between opposing features must be reached.…”

Section: Discussionmentioning

confidence: 99%

Advances and obstacles in pressure-driven solid-state cooling: A review of barocaloric materials

Lloveras

Tamarit

2021

MRS Energy & Sustainability

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Solid-state caloric effects promise since decades a disruptive cooling technology that should be more efficient and cleaner than current vapor compression. However, despite relevant achievements have been made, it is still difficult to foresee the time left for the development and wide implementation of competitive devices. Recent progress in the response of materials under hydrostatic pressure offers hope for overcoming some of the shortcomings posed by other solid-state methods and augurs a good outlook for barocaloric cooling, but there are still many struggles ahead to address in order to demonstrate its viability as a commercial cooling technique. Here we briefly review the milestones achieved in terms of barocaloric materials and discuss the pending challenges and expectations for the oncoming years.

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“…On the other hand, powdered materials display lower thermal conductivities than their single crystal counterparts because the free path is shortened due to phonon scattering at the grain boundary. However, powder can be combined with a small percentage of excellent conducting nanoparticles [53] or embedded in highly conductive porous matrix [54][55][56][57][58] resulting in a composite with notably improved thermal conductivity. Finally, as an added value for technological applications, it must be noted that both compounds under study are of low cost, low toxicity (irritant) and nonhazardous [59,60].…”

Section: Discussionmentioning

confidence: 99%

Reversible colossal barocaloric effects near room temperature in 1-X-adamantane (X=Cl, Br) plastic crystals

Aznar

Négrier

Planes

et al. 2021

Applied Materials Today

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Plastic crystals undergo phase transitions with unusually large volume and entropy changes related to strong molecular orientational disordering. These features have led to a resurgent interest in these materials because recently they have shown great potential in solid-state cooling applications driven by pressure. Here we demonstrate that two plastic crystals derived from adamantane -1-Br-adamantane and 1-Cl-adamantane-undergo colossal reversible barocaloric effects under moderate pressure changes in a wide temperature span near room temperature thanks to a relatively small hysteresis and very high sensitivity of the transition temperature to pressure. In particular, 1-Cl-adamantane displays an optimal operational temperature range covering from ~40 K below and up to room temperature, and under a pressure change of 1 kbar this compound outperforms any other barocaloric material known so far. Our work gives strong support to plastic crystals as best candidates for barocaloric cooling. We also provide insight into the physical origin of the entropy changes through the analysis of the disorder on the involved phases.

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Effects of site-occupation disorder on the low-temperature thermal conductivity of molecular crystals

Cited by 13 publications

References 73 publications

Emergence of glassy features in halomethane crystals

Emergence of glassy features in halomethane crystals

Advances and obstacles in pressure-driven solid-state cooling: A review of barocaloric materials

Reversible colossal barocaloric effects near room temperature in 1-X-adamantane (X=Cl, Br) plastic crystals

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