Current interest in barocaloric effects has been stimulated by the discovery that these pressure-driven thermal changes can be giant near ferroic phase transitions in materials that display magnetic or electrical order. Here we demonstrate giant inverse barocaloric effects in the solid electrolyte AgI, near its superionic phase transition at ~420 K. Over a wide range of temperatures, hydrostatic pressure changes of 2.5 kbar yield large and reversible barocaloric effects, resulting in large values of refrigerant capacity. Moreover, the peak values of isothermal entropy change (60 J K⁻¹ kg⁻¹ or 0.34 J K⁻¹ cm⁻³) and adiabatic temperature changes (18 K), which we identify for a starting temperature of 390 K, exceed all values previously recorded for barocaloric materials. Our work should therefore inspire the study of barocaloric effects in a wide range of solid electrolytes, as well as the parallel development of cooling devices.

The dynamics of a simple rigid pseudoglobular molecule (2-adamantanone) has been studied by means of dielectric spectroscopy and examined under the constraints imposed by the space group of the crystal structure determined by x-ray powder diffraction. The low-temperature monoclinic structure of 2-adamantanone, with one molecule per asymmetric unit (Z$'${}=1), displays a statistical intrinsic disorder, concerning the site occupancy of the oxygen atom along three different sites. Such a physically identifiable disorder gives rise to large-angle molecular rotations which inherently lead to time-average fluctuations of the molecular dipole, thus contributing to the dielectric susceptibility. The dielectric spectra for the low-temperature ``ordered'' phase displays a universal feature of glassy-like materials, i.e., coexistence of $\alpha${}- and $\beta${}-relaxation processes. The former is clearly identified with the strongly restricted reorientational motions within the long-range ``ordered'' crystalline lattice. The latter, never observed before in fully translationally and highly orientationally ordered phases, displays all the properties of an original Johari-Goldstein $\beta${}-relaxation, in spite of the strong character of this glass-like phase. These findings can be explained according to the coupling model, applied to such ``ordered'' phases.

We probe the temperature- and pressure-dependent specific volume (v) and dipolar dynamics of the amorphous phase (in both the supercooled liquid and glass states) of the ternidazole drug (TDZ). Three molecular dynamic processes are identified by means of dielectric spectroscopy, namely the α relaxation, which vitrifies at the glass transition, a Johari-Goldstein β_JG relaxation, and an intramolecular process associated with the relaxation motion of the propanol chain of the TDZ molecule. The lineshapes of dielectric spectra characterized by the same relaxation time (isochronal spectra) are virtually identical, within the studied temperature and pressure ranges, so that the time-temperature-pressure superposition principle holds for TDZ. The α and β_JG relaxation times fulfil the density-dependent thermodynamic scaling: master curves result when they are plotted against the thermodynamic quantity Tv ^γ , with thermodynamic exponent γ approximately equal to 2. These results show that the dynamics of TDZ, a system characterized by strong hydrogen bonding, is characterized by an isomorphism similar to that of van-der-Waals systems. The low value of γ can be rationalized in terms of the relatively weak density-dependence of the dynamics of hydrogen-bonded systems.

We study the temperature-dependent molecular dynamics, ion conduction, and phase behavior of plastic-crystal electrolytes based on the succinonitrile molecule. We employ calorimetry and dielectric spectroscopy to probe binary mixtures of succinonitrile with glutaronitrile or acetonitrile and also analyze the effect of dissolving lithium salts in these systems. The glutaronitrile–succinonitrile mixture has the highest conductivity, and it is the only plastic-crystal system that displays a perfect correlation between the ion drift and the on-site reorientational dynamics. Doping with lithium ions boosts the conductivity but breaks such perfect correlation. All of these features can be rationalized by assuming that conduction is due to the self-diffusion of a minority of ionized dinitrile molecules. Doping with lithium salts slows down the collective molecular dynamics while leaving the intramolecular relaxation motion unaffected. All samples exhibit a very broad melting transition and exist in a mixed liqui...

Due to its high energy efficiency and environmental friendliness, solid-state cooling based on the barocaloric (BC) effect represents a promising alternative to traditional refrigeration technologies relying on greenhouse gases. Plastic crystals displaying orientational order-disorder solid-solid phase transitions have emerged among the most gifted materials on which to realize the full potential of BC solid-state cooling. However, a comprehensive understanding of the atomistic mechanisms on which order-disorder BC effects are sustained is still missing, and rigorous and systematic methods for quantitatively evaluating and anticipating them have not been yet established. Here, we present a computational approach for the assessment and prediction of BC effects in orientationally disordered materials that relies on atomistic molecular dynamics simulations and emulates quasi-direct calorimetric BC measurements. Remarkably, the proposed computational approach allows for a precise determination of the partial contributions to the total entropy stemming from the vibrational and molecular orientational degrees of freedom. Our BC simulation method is applied on the technologically relevant material CH₃NH₃PbI₃ (MAPI), finding giant BC isothermal entropy changes (∣ΔS_BC∣ ~ 10 J K⁻¹ kg⁻¹) under moderate pressure shifts of ~0.1 GPa. Intriguingly, our computational analysis of MAPI reveals that changes in the vibrational degrees of freedom of the molecular cations, not their reorientational motion, have a major influence on the entropy change that accompanies the order-disorder solid-solid phase transition.

We present a dynamic and thermodynamic study of the orientational glass former Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane, ${\mathrm{CCl}}_2\mathrm{F}\text{−}{\mathrm{CClF}}_2$) in order to analyze its kinetic and thermodynamic fragilities. Freon 113 displays internal molecular degrees of freedom that promote a complex energy landscape. Experimental specific heat and its microscopic origin, the vibrational density of states from inelastic neutron scattering, together with the orientational dynamics obtained by means of dielectric spectroscopy have revealed the highest fragility value, both thermodynamic and kinetic, found for this orientational glass former. The excess in both Debye-reduced specific heat and density of states (boson peak) evidences the existence of glassy low-energy excitations. We demonstrate that early proposed correlations between the boson peak and the Debye specific heat value are elusive as revealed by the clear counterexample of the studied case.