Dielectric study of orientational disorder in (CO2)1−x(N2O)xmixed crystals

The dipolar relaxation dynamics of solid solutions of carbon dioxide and nitrous oxide has been investigated using dielectric spectroscopy. The temperature dependence of the relaxation rate reveals an ideal Arrhenius behavior for all concentrations, with energy barriers which scale linearly between the two pure compounds. The attempt frequencies are anomalously high. The distribution of relaxation times due to the static random fields as introduced by the substitutional impurity molecules is almost negligible. The melting temperature is determined by a critical relaxation rate of 40 kHz.

Dynamics of supercooled liquids and glassy solids

Single particle jumps and correlated ionic motions in glass-ceramics

Using impedance spectroscopy, the ion transport in poorly Li-conducting aluminosilicate glass ceramics and their precursor glasses has been measured for temperatures 50 K < T < 550 K and covering a frequency range of more than 14 decades from 10 mHz up to 3 THz. In addition to the familiar cooperative ionic motion dominating at high temperatures, for the first time dielectric relaxation due to elementary hopping processes is observed well below room temperature.

Correlations of the nonexponentiality and state dependence of mechanical relaxations with bond connectivity in Ge-As-Se supercooled liquids

We have studied the mechanical responses of supercooled Ge-As-Se liquids to flexural strains and temperature steps. The departures from exponential relaxation correlate well with the variations in connectivity. The structural state dependence of the mechanical relaxation, detected in pure and weakly cross-linked Se, is suppressed completely at the rigidity percolation threshold {l angle}{ital r}{sub {ital c}}{r angle}, where the liquid fragility is a minimum. The shapes of the decay functions of samples with the same {l angle}{ital r}{sub {ital c}}{r angle} but different compositions are not universal at {ital T}{sub {ital g}} probably because of chemical effects near the binary edges of th…

87RbNMR spectra of hydrogen-bondedRb3D(SO4)2andRb3H(SO4)2crystals

The paraelectric and antiferroelectric phases of ${\mathrm{Rb}}_{3}{\mathrm{D}(\mathrm{S}\mathrm{O}}_{4}{)}_{2}$ and ${\mathrm{Rb}}_{3}{\mathrm{H}(\mathrm{S}\mathrm{O}}_{4}{)}_{2}$ were investigated using rubidium NMR. The angle dependence of the second order quadrupole shifted central ${}^{87}\mathrm{Rb}$ transitions was recorded at 300 K. It was found to be in full agreement with the symmetry elements of a monoclinic $A2/a$ structure. The temperature dependence of the magnitude and asymmetry of the electrical field gradient (EFG) tensors at the Rb sites was determined using powder samples and revealed no differences between protonated and deuterated specimens. The antiferroelectric transi…

Reorientational dynamics in simple supercooled liquids

Abstract The geometry of the reorientational dynamics in the van der Waals liquid, toluene, and the hydrogen bond network, glycerol, are compared. Both systems have contributions from small angle fluctuations. In glycerol the fraction of these small angle fluctuations is much larger than in toluene, due to the stronger anisotropic interactions in the former substance. The average reorientational angle in both systems is similar and on the order of 10 ∘ . In addition we analyze the stretching of the rotational correlation functions of rank one and two. In both cases we find that the second rank correlation function has a more pronounced stretching than the corresponding first rank correlatio…

Quantum paraelectric and induced ferroelectric states in

Nominally pure has been studied by dielectric spectroscopy using small (linear regime) as well as large electrical fields (non-linear regime) up to . In addition measurements of the specific heat and its field-dependent contribution have been carried out. The field dependence of the dielectric constant and the specific heat can be well described by the transverse Ising Hamiltonian including tunnelling and external field terms. It gives evidence for the existence of polar clusters at low temperatures which are supposed to be associated with the quantum paraelectric state below in accord with recent free-energy calculations. The low-field third-harmonic susceptibility which measures the polar…

β-Relaxation and low-temperature specific heat in (KBr)1?x(KCN)x

The specific heat in (KBr)1−x(KCN)x has been measured for concentrations 0.00≦x≦0.93 and for temperatures 2 K≦T≦50 K. In addition, the dipolar relaxation phenomena were studied using dielectric spectroscopy. The relaxation behaviour was parametrized assuming a Gaussian distribution of energy barriers and the mean activation energies, the distribution widths, and the attempt frequencies have been determined as a function of the CN− concentration. With these parameters the linear and the excess specific heat contributions were calculated and compared to the calorimetric results.

Experimental Determination of Four-Time Stimulated Echoes in Liquids, Colloidal Suspensions, and Crystals

Four-time stimulated echo experiments have been used to monitor the temporal evolution of the reorientation rates of deuterated molecules or colloidal suspensions. We present extended phase cycles for this seven-pulse experiment. In order to test its performance three vastly different materials are chosen. These include a crystal in which the molecules carry out well-defined 180 degrees flips and a supercooled liquid characterized by a distribution of jump angles centered around 10 degrees. As an example for rotational diffusion, data on a concentrated suspension of polystyrene spheres in a viscous medium are presented. Copyright 1998 Academic Press.

Ion transport in the fragile glass former3KNO3-2Ca(NO3)2

The molten salt ${3\mathrm{K}\mathrm{N}\mathrm{O}}_{3}$-2Ca(${\mathrm{NO}}_{3}$${)}_{2}$ has been studied in the frequency range 5 mHz40 GHz and for temperatures 10 KT500 K using impedance spectroscopy. It is found that in the microwave regime the dynamic conductivity traces the primary response. In the radio- and audio-frequency ranges the mobile ion relaxation becomes increasingly decoupled and the time scale and stretching of the response as determined from electrical modulus spectra differ from those obtained by spectroscopies probing the structural response. For T\ensuremath{\gtrsim}360 K minima are detected in the dielectric loss that make possible a comparison with recent mode-coupli…

Long-lived dynamic heterogeneity in a relaxor ferroelectric

The polydispersive dielectric response of the relaxor ferroelectric lead magnesium niobate was investigated using nonresonant spectral hole-burning experiments. Using large alternating electric fields, specific parts of the relaxation-time distribution could be addressed selectively. This provides evidence for the dynamic heterogeneity of the dipolar reorientation process. The refilling of single as well as of double holes was much slower than the time scale set by the pump frequencies. Upon refilling, the holes exhibited no signs of spectral broadening. The present findings suggest a speedup of polarization response associated with a domain-wall depinning that is induced by the hole-burnin…

Dipolar and quadrupolar freezing in (NaCN)1−x(KCN)x

Magnetic Resonance Studies of the Heterogeneous Rotational and Translational dynamics in Disordered Materials

Static freezing transition at a finite temperature in a quasi-one-dimensional deuteron glass.

The dipolar freezing process of a quasi-one-dimensional betaine deuteron glass was studied using linear and nonlinear dielectric spectroscopy. The linear response as measured for frequencies $5\mathrm{mHz}l\ensuremath{\nu}l200\mathrm{MHz}$ was analyzed using the recently invented $\ensuremath{\delta}$ plot, providing evidence for a static freezing transition near 30 K. Measurements of the ergodic to nonergodic transition as well as of the incipient divergence of the nonlinear susceptibility yield independent confirmation of this quasistatic freezing transition temperature. The critical exponent describing the nonlinear behavior is found to be $\ensuremath{\gamma}\phantom{\rule{0ex}{0ex}}=\p…

The orientational glass studied by nuclear magnetic resonance

Single crystals of the orientational glass have been studied using iodine NMR for temperatures 1.8 K < T < 300 K. Two-dimensional spectroscopy has shown that the quadrupole-perturbed central transitions are predominantly inhomogeneously broadened. The orientational glass transition is already accompanied by a considerable increase of that broadening in the regime of fast motion. Evidence for a random-field smearing of the random-bond-induced freezing process is obtained. Measurements of the spin - lattice relaxation time reveal the existence of a broad distribution of orientational correlation times at low temperatures.

Non-exponential relaxation in disordered materials: Phenomenological correlations and spectrally selective experiments

Abstract In most glass-forming materials external perturbations are relaxed in a non-exponential fashion. It is shown that the degree of non-exponentiality is phenomenologically correlated with the departure from simple thermally activated behavior as measured by the fragility index m. In model glass formers such as the Ge-As-Se ternary alloy, and to some degree for amorphous materials in general, the correlations with these properties are observed also for other characteristic features. These include the specific heat step and the aging kinetics in the glass transformation range. While phenomenological correlations have proven very useful for rationalizing the properties of many glass form…

Non-ideal mixing behavior in dibutyl phosphate-propylamine binary liquids: Dielectric and nuclear magnetic resonance investigations

Abstract Owing to the amphiphilic nature of their constituent molecules, binary mixtures of pure liquid surfactants are usually characterized by enhanced nano-segregation and thus can exhibit interesting transport properties and complex macroscopic behavior. In this ambit it was recently shown by Turco Liveri et al. (J. Mol. Liq. 263 (2018) 274–281) at room temperature that mixtures of short aliphatic chains compounds, such as dibutyl phosphate (DBP) and n-propylamine (PA) liquids, due to their ability to allow for phosphate-to-amine proton transfer, display ionic liquid–like behavior with composition-dependent enhanced conductivity, viscosity, and magnetically-induced birefringence. To und…

Relaxation dynamics in orientational glasses

Abstract The multipolar relaxation dynamics observed in dipolar and quadrupolar glasses are reviewed. Special attention is given to the distribution of the relaxation times and to the temperature dependence of the mean relaxation rates. Experimental evidence is provided that orientational glasses can be described in terms of ‘strong glasses’ that are characterized by a low density of configurational states in the potential energy surface. It is suggested that this behavior results from the natural separation of timescales of reorientational and diffusive processes in these crystals.

Amorphous polymorphis in ice investigated by inelastic neutron scattering

Abstract High-density Ilda and low-density Ilda amorphous have been investigated by inelastic neutron scattering (INS) with emphasis on the energy window from 0.5 to 20 meV. At variance with earlier measurements the spectra in the Ilda phase show a simple ω2 behaviour in the acoustic region and the temperature dependence is found to be harmonic. Ilda converts with a strongly temperature-dependent rate towards Ilda ice. We have investigated in detail the time evolution of both the static and dynamic response functions at several temperatures. Elastic small-angle signals indicate the presence of strong heterogeneties at the early stages of the conversion process. At least two different time s…

Ionic transport and heat capacity of glass-forming metalnitrate mixtures

Abstract Ionic transport of the glass-forming metalnitrate mixtures [Ca(NO 3 ) 2 ] 0.44 [KNO 3 ] 0.56 (MKN), and [Mg(NO 3 ) 2 ] 0.44 [NaNO 3 ] 0.56 (MNN) was investigated near the glass transition using broadband spectroscopy of the complex conductivity to 300 MHz. The real part of the conductivity exhibits a transition from frequency independent to power law behavior as found in most ionic conductors. At high frequencies the frequency exponent approaches unity and becomes larger at low temperatures. In the real part of the dielectric constant, a relaxation step could be observed in CRN. A detailed evaluation of the results within the modulus formalism is presented. The imaginary part of t…

Antiferroelectric phase transition inRb3D(SO4)2single crystals studied by87RbNMR

The quadrupole perturbed central transition of the magnetic ${}^{87}\mathrm{Rb}$ resonance was used to study ${\mathrm{Rb}}_{3}{\mathrm{D}(\mathrm{S}\mathrm{O}}_{4}{)}_{2}$ single crystals. Three resonance lines were found at room temperature. This result is in accord with the monoclinic space group reported for these crystals and does not require the previously invoked self-trapped proton states. The number of resonance lines quadruples below the antiferroelectric phase transition near 82 K. From the line splitting the order-parameter exponent of the low-temperature phase was found to be $\ensuremath{\beta}=0.2.$ Spin-lattice relaxation times have been determined in the fully protonated an…

Correlation of primary relaxations and high-frequency modes in supercooled liquids. I. Theoretical background of a nuclear magnetic resonance experiment

The question regarding a possible correlation of the time scales of primary and secondary relaxations in supercooled liquids is formulated quantitatively. It is shown how this question can be answered using spin-lattice relaxation weighted stimulated-echo experiments, which are presented in an accompanying paper [A. Nowaczyk, B. Geil, G. Hinze, and R. Böhmer, Phys. Rev. E 74, 041505 (2006)]. General theoretical expressions relevant for the description of such experiments in the presence of correlation effects are derived. These expressions are analyzed by Monte Carlo integration for various correlation scenarios also including exchange processes, which are the hallmark of dynamical heteroge…

Heterogeneity at the glass transition: what do we know?

We critically discuss the information that can be obtained from experiments with respect to the existence, the life time, and the length scale of dynamical heterogeneity in glass-forming liquids. The ability to select a dynamically distinguishable subensemble and observe its return to the full equilibrium ensemble is illustrated by examples from multi-dimensional NMR. We also discuss non-resonant hole burning spectroscopy as an example for which two separate time scales are involved.

Comment on “Hole-Burning Experiments within Glassy Models with Infinite Range Interactions”

Comment on: L.F. Cugliandolo and J.L. Iguain; Phys. Rev. Lett. {\bf 85} 3448 (2000)

Correlation of primary relaxations and high-frequency modes in supercooled liquids. II. Evidence from spin-lattice relaxation weighted stimulated-echo spectroscopy

Using spin-lattice relaxation weighted stimulated-echo spectroscopy, we report evidence for a correlation of the primary and secondary relaxation times. The experiments are performed using deuteron nuclear magnetic resonance somewhat above the calorimetric glass-transition of ortho-terphenyl, D-sorbitol, and cresolphthalein-dimethylether. The data analysis is based on the procedure outlined in the accompanying theoretical paper [B. Geil, G. Diezemann, and R. B\"ohmer, Phys. Rev. E 74, 041504 (2006)]. Direct experimental evidence for a modified spin-lattice relaxation is obtained from measurements on a methyl deuterated acetyl salicylic acid glass. The limitations of the present experimental…

Isotope effects on the dynamics of a supercooled van der Waals liquid

Deuteron magnetic resonance was used to study three differently isotope-labeled species of the fragile glass-forming liquid ortho-terphenyl. The calorimetric glass transition of the isotope deuterated only at the central phenyl ring is significantly lower than that of the perdeuterated one. It is shown that while the ortho-terphenyl molecule is not as rigid as previously often assumed, its overall reorientation geometry is independent of deuteration. The characteristic jump angles are found to increase with temperature, thus resolving an apparent discrepancy previously noted when comparing typical jump sizes from NMR with other data.

Elastic and quasielastic neutron scattering studies in KBr:KCN mixed crystals

Neutron scattering studies in (KBr)1–x(KCN)x mixed crystals are presented utilizing powder diffraction, single crystal diffraction and time-of-flight techniques. Forx&gt;0.6 (KBr)1–x(KCN)x crystals exhibit ferroelastic and ferroelectric low-temperature phases. Crystals withx&lt;0.6 undergo transitions into an orientational glass state. Here we present a detailed phase diagram including new results for x=0.85 and x=0.65. For the latter system a stable rhombohedral low-temperature phase has been detected where the orientational disorder of the plastic phase is only partly removed and quadrupolar relaxations between three body diagonals are still possible. From the powder diffraction experimen…

Polar relaxation mode in pure and iron-doped barium titanate

A dielectric relaxation peak is reported in ${\mathrm{BaTiO}}_{3}$ and in ${\mathrm{BaTi}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{O}}_{3}$. It is nearly monodispersive, centered in the ${10}^{8}$-Hz range, and slowest at the transition temperature ${T}_{c}$\ensuremath{\simeq}413 K from the cubic to the tetragonal phase. Iron doping lowers ${T}_{c}$ and slows down this relaxation mode.

Hembergeret al.Reply:

The glass transition in (KI)0.5(ND4I)0.5 mixed crystals as studied by deuteron spin-lattice relaxation

Abstract Nuclear spin resonance has been used to study the deuteron magnetization recovery in (KI)0.5(ND4I)0.5 mixed crystals. At high temperatures the spin-lattice-relaxation is exponential. For T ⪅ 45 K deviations from this simple behaviour occur, signalling the onset of spatial inhomogeneities due to the formation of an orientational glass. The results demonstrate that the transition of (KI)0.5(ND4I)0.5 into the glassy state is driven by the freezing of random bonds.

Nuclear Spin Relaxation in Viscous Liquids: Relaxation Stretching of Single-Particle Probes

Spin-lattice relaxation rates R1(ω,T), probed via high-field and field-cycling nuclear magnetic resonance (NMR), are used to test the validity of frequency-temperature superposition (FTS) for the reorientation dynamics in viscous liquids. For several liquids, FTS is found to apply so that master curves can be generated. The susceptibility spectra are highly similar to those obtained from depolarized light scattering (DLS) and reveal an excess wing. Where FTS works, two approaches are suggested to access the susceptibility: (i) a plot of deuteron R1(T) vs the spin-spin relaxation rate R2(T) and (ii) a plot of R1(T) vs an independently measured reference time τref(T). Using single-frequency s…

Nonresonant Spectral Hole Burning in the Slow Dielectric Response of Supercooled Liquids

Large-amplitude, low-frequency electric fields can be used to burn spectral holes in the dielectric response of supercooled propylene carbonate and glycerol. This ability to selectively modify the dielectric response establishes that the non-Debye behavior results from a distribution of relaxation times. Refilling of the spectral hole was consistent with a single recovery time that coincided with the peak in the distribution. Moreover, refilling occurred without significant broadening, which indicates negligible direct exchange between the degrees of freedom that responded to the field. Nonresonant spectral hole burning facilitates direct investigation of the intrinsic response of systems t…

Surface-induced order and diffusion in 5CB liquid crystal confined to porous glass.

Liquid crystals confined into small cavities are known to have a weak orientational order even above the nematic-isotropic transition temperature. The surface-induced order and molecular dynamics in this temperature range are studied with the aid of deuteron NMR spectra, spin relaxation times T(1) and T(2,) proton dipolar-correlation effect, and direct measurements of the effective diffusion coefficient for the liquid crystal 5CB confined to controlled-pore glasses. Our results show that an arrangement of molecules parallel to the wall is induced by local molecular interactions between the liquid crystal and solid, resulting in a weak and temperature independent surface order parameter, S(0…

Aging, rejuvenation, and memory phenomena in a lead-based relaxor ferroelectric

Isothermal aging and temperature cycle experiments were done on the relaxor ferroelectric lead magnesium niobate mixed with 10% lead titanate (PMN-10PT) around and below the diffuse maximum of the dielectric loss. With increasing aging time tw the isothermal evolution of the linear susceptibility follows a power law and does not show frequency scaling. The non-linear susceptibility, however, obeys nearly perfect ωt w-scaling. After aging the sample at a single temperature we observed both rejuvenation and memory effects in temperature cycle experiments. This observation indicates symmetric behavior in the sense that it shows up irrespective of whether cooling with subsequent re-heating or h…

Deuteron NMR investigations of glass and phase transitions in(KI)1−x(ND4I)xmixed crystals

Powdered potassium ammonium iodide mixed crystals with ammonium concentrations of 20% and 70% have been studied using deuteron NMR techniques. For the less doped sample the deuteron line starts to broaden and the spin-lattice relaxation time ${T}_{1}$ becomes nonexponential below about 20 K. These observations indicate the breakdown of ergodicity and the onset of orientational glass freezing. At the lowest temperatures ${T}_{1}$ reaches a plateau value. For the 70% sample a relatively abrupt onset of two-phase behavior at $Tl35\mathrm{K}$ is inferred from measurements of the spin-spin and spin-lattice relaxation times. These observations are taken to indicate an order-disorder transition to…

Dipolar and Quadrupolar Freezing in(KBr)1−x(KCN)x

Dipolar and quadrupolar susceptibility measurements are reported for the molecular glass system ${(\mathrm{KBr})}_{1\ensuremath{-}x}{(\mathrm{KCN})}_{x}$ covering a wide range of frequencies. The results allow a direct comparison of the dipolar and quadrupolar anomalies and demonstrate unambiguously that the freezing in of the dipolar and quadrupolar degrees of freedom occurs at different temperatures.

Far-off-resonance averaging of dipolar interactions in solids

Abstract The far-off-resonance performance of several line-narrowing sequences is investigated. Both theoretically and experimentally, it is found that transverse relaxation times, dominated by dipole–dipole interactions, are most effectively prolonged not only on-resonance but also for certain, generally large, resonance offsets. These correspond to a situation when, during the basic pulse separation, the frequency offset rotates the toggling-frame Hamiltonian by multiples of 180°. The implications of these results for the study of macroscopic translational diffusion using static-field-gradient NMR are discussed.

Structural relaxation in a molten salt probed by time-dependent dc conductivity measurements

Abstract Time-dependent dc conductivity was measured after cooling steps of about 2 K in the glass transformation range of 2Ca(NO 3 ) 2 -3RbNO 3 . The shape and time scale of the structural relaxation function was thus monitored for times 60 s t 6 s. The time scale could be compared with results from scanning calorimetry measurements and good agreement was found. From the heat capacity data and from the solid state conductivity the expected liquid state conductivity relaxation time was calculated using several models. The good compatibility of these calculations with the experimental results provides evidence that near the calorimetric glass transition the mobile ions perform concerted moti…

Slow Dielectric Relaxation of Supercooled Liqutos Investigated by Nonresonant Spectral Hole Burning

ABSTRACTWhen supercooled propylene carbonate and glycerol are subjected to a large-amplitude, low-frequency electric field, a spectral hole develops in their dielectric relaxation that is significantly narrower than their bulk response. This observation of nonresonant spectral hole burning establishes that the non-Debye response is due to a distribution of relaxation times. Refilling of the spectral hole occurs abruptly, indicative of a single recovery rate that corresponds to the peak in the distribution. The general shape of the spectral hole is preserved during recovery, indicating negligible interaction between the degrees of freedom that responded to the field. All relevant features in…

Spatial heterogeneity in glassy polystyrene detected by deuteron NMR relaxation

Using deuteron NMR, the dynamics of supercooled polystyrene-d 3 was investigated near the calorimetric glass transition. At these temperatures non-exponential spin lattice relaxation is found, indicating the presence of spatial heterogeneity. With increasing temperature, structural relaxation becomes fast enough to average efficiently over different spatial environments, leading to exponential magnetization decays. A qualitative comparison with toluene as a representative of a low molecular weight glass former is carried out. Indications are found that in polystyrene the observed averaging process is more effective at T g than it is in toluene.

X-ray diffraction, optical birefringence, and87Rb nuclear magnetic resonance spectroscopy of the paraelectric and antiferroelectric phases of Rb3DxH1-x(SO4)2

The antiferroelectric (AFE) phase transition of Rb3DxH1-x(SO4)2 was studied using x-ray diffraction, optical birefringence, and nuclear magnetic resonance. The orientation dependence of the resonance lines deduced from the quadrupole-perturbed 87Rb nuclear magnetic resonance of Rb3D(SO4)2 single crystals indicates slight deviations from the monoclinic symmetry in the paraelectric and the AFE phases. The dynamical critical exponents as deduced from measurements of the spin-lattice relaxation times depend on the deuteron concentration. Additionally, we have carried out x-ray single-crystal diffraction as well as optical birefringence measurements and find clear evidence for a structural phase…

Dynamic heterogeneity in supercooled ortho-terphenyl studied by multidimensional deuteron NMR

Using deuteron NMR, we have studied molecular reorientation rates and rate exchange processes in supercooled ortho-terphenyl. We monitor the re-equilibration of differently selected subensembles through four-time stimulated echo experiments. A comparison of the two-time with the four-time echoes suggests that the characteristic time scales for reorientation and dynamical exchange are relatively similar. The four-time correlation functions were described using various multi-state rate exchange models.

Correlation of primary and secondary relaxations in a supercooled liquid

The widespread assumption that primary and secondary relaxations in glass-forming materials are independent processes is scrutinized using spin-lattice relaxation weighted stimulated-echo spectroscopy. This nuclear magnetic resonance (NMR) technique is simultaneously sensitive to the dynamics on well-separated time scales. For the deeply supercooled liquid sorbitol, which exhibits a strong secondary relaxation, the primary relaxation (that is observable using NMR) can be modified by suppressing the contributions of those subensembles which are characterized by relatively slow secondary relaxations. This is clear evidence for a correlation between primary and secondary relaxation times. In t…

Nanoscale heterogeneity if glass-forming liquids: experimental advances

Abstract Recent evidence indicates that in supercooled liquids the cooperativity of molecular motion extends over certain temporal and spatial ranges. A key advance is the experimental and theoretical exploration of higher-order correlation functions that can track the molecular coordinates for more than just two points in time or space. Uncontested experimental determinations of the heterogeneity length scale at the glass transition remain a major goal.

Heterogeneous and Homogeneous Diffusivity in an Ion-Conducting Glass

The nature of ion diffusivity in the vitreous conductor 2Ca NO3 2 ? 3KNO3 (CKN) was studied by nonresonant dielectric hole burning. Spectral holes in the electric field relaxation are probed subsequent to a high electric sinusoidal burn field. For sufficiently high pump frequencies we are able to induce spectrally selective modifications in the relaxation of the electric modulus, indicating that ionic diffusivity is a spatially varying quantity in glassy CKN. Homogeneous behavior occurs in the regime of low pump frequencies, in which the resistivity approaches its steady state value. Thus, longer-ranged ionic motions lead to a spatial averaging over the heterogeneity of local ion diffusivit…

Aging in a free-energy landscape model for glassy relaxation. II. Fluctuation-dissipation relations.

Several fluctuation-dissipation relations are investigated for a simple free-energy landscape model designed to describe the primary relaxation in supercooled liquids. The calculations of the response and of the correlation functions are performed for a quench from a high temperature to a low temperature. In the model, all dynamical quantities reach equilibrium after long times, but for times shorter than the re-equilibration time they do not exhibit time-translational invariance and the fluctuation-dissipation theorem is violated. Two measures for these violations are considered. One such measure is given by the slope in a plot of the integrated response versus the correlation function and…

Relaxation times at the rate-dependent glass transition

The structural relaxation time near the cooling rate dependent glass transition is determined self-consistently within the Moynihan-Narayanaswami formalism. In order to illustrate the method we analyze scanning calorimetry data from amorphous calcium-rubidium nitrate. A characteristic time scale of about 250 s is obtained at the conventionally defined glass transition. The occurrence of decoupled, faster relaxation modes is briefly discussed.

Capacitive scanning dilatometry and frequency-dependent thermal expansion of polymer films

The dilatometric properties of polymer films near and above their glass-transition temperatures were explored using capacitive high-frequency detection in temperature ramping as well as in harmonic temperature cycling experiments. The broad applicability of capacitive scanning dilatometry is demonstrated by the investigation of macromolecular systems of vastly different polarity such as polystyrene, polybutadiene, and polyvinylacetate. From temperature cycling experiments the real and imaginary parts of the frequency-dependent thermal-expansion coefficient are determined in the sub-Hz regime.

Nature of the non-exponential primary relaxation in structural glass-formers probed by dynamically selective experiments

Several experimental methods feature the potential to distinguish between slow and fast contributions to the non-exponential, ensemble averaged primary response in glass-forming materials. Some of these techniques are based on the selection of subensembles using multi-dimensional nuclear magnetic resonance, optical bleaching, and non-resonant spectral hole burning. Others, such as the time-dependent solvation spectroscopy, measure microscopic responses induced by local perturbations. Using several of these methods it could be demonstrated for various glass-forming materials that the non-exponential relaxation results from a superposition of dynamically distinguishable entities. The experime…

Proton glass behavior and hopping conductivity in solid solutions of antiferroelectric betaine phosphate and ferroelectric betaine phosphite.

Measurements of the dielectric permittivity are reported for solid solutions of antiferroelectric betaine phosphate and ferroelectric betaine phosphite at frequencies 10 −2 Hz T c the dielectric response is dominated by ac and dc conduction. The 40% sample exhibits pure relational behavior indicative of a transition into an orientational glass state

Relaxational dynamics at the class transition in orientational and canonical glasses investigated by dielectric spectroscopy

Abstract Measurements of the dielectric permittivity are reported for the canonical glass glycerol and for solid solutions of ferroelectric betaine phosphite and ferroelectric betaine phosphate, which can be viewed as protype systems of orientational glasses. In this latter system long range dipolar order is suppressed by the competing ferroelectric and antiferroelectric interactions and the dipolar moments freeze-in devoid of long range order. In both systems the relaxation dynamics is studied for frequencies 10−2Hz≤ν≤106Hz, close to the glass transition temperature. The relaxation dynamics is characterized according to Angell's classification scheme of strong and fragile glass-formers.

Dynamic thermal expansivity near the glass transition

Dielectric techniques were used to investigate the thermal expansivity of polystyrene films. Capacitive scanning dilatometry (CSD) employs temperature ramping in order to monitor the non-linear structural relaxation in the glass transformation range and to quantify liquid fragility. In the linear response regime, the complex thermal expansivity is obtained as a function of the temperature cycling frequency and is observed to reflect the structural relaxation.

Slow and fast methyl group rotations in fragile glass-formers studied by NMR

Abstract The spin-lattice relaxation times of the selectively ring deuterated, fragile glass-formers propylene carbonate and toluene were compared with those measured for species which were specifically labeled at the methyl groups. It was found that the dynamics of the CD 3 group is strongly decoupled from that associated with the primary response of toluene, while for propylene carbonate the degree of decoupling is relatively weak. The experimental results could be described successfully using a model which takes into account the ring dynamics as well as those of the methyl group.

Phase transition kinetics and reorientational dynamics of the plastic crystal meta-carborane studied by deuteron NMR

Meta-carborane shows an orientationally disordered, orthorhombic phase which transforms into an ordered monoclinic phase near 170 K and into a quasi-isotropic cubic phase near 280 K. From deuteron magnetization measurements both transitions are found to exhibit a thermal hysteresis and slow transformation kinetics. Furthermore, solid-echo NMR spectra and spin-lattice relaxation times are reported. These results indicate that in the orthorhombic phase the meta-carborane molecules perform a strongly anisotropic motion which is characterized by a temperature dependent amplitude.

Stimulated 7^Li echo NMR spectroscopy of slow ionic motions in a solid electrolyte

Abstract Lithium spin-alignment spectroscopy is presented as an NMR technique for studying slow translational motions in solid and solid-like ionic conductors. We employ phase cycling that allows to measure two-time translational correlation functions via the generation of a pure quadrupolar ordered state. Correlation functions of the crystalline electrolyte Li 3 Sc 2 (PO 4 ) 3 were recorded for times ranging from about 0.1 ms to more than 10 s, implying that translational diffusion coefficients smaller than 10 −20 m 2 /s become accessible.

Reorientations and translations in a fragile glass-former: magnetic resonance studies of meta-fluoroaniline

Abstract The rotational dynamics in supercooled liquid and glassy meta-fluoroaniline was studied using proton and fluorine spin-lattice relaxation times. It is shown that while proton relaxation is dominated by homonuclear relaxation, for fluorine heteronuclear relaxation prevails. The results could be well described using a distribution of correlation times. The mean correlation times show pronounced deviations from the simple Arrhenius law. In addition translational self-diffusion coefficients were measured for T>200 K using a static magnetic field gradient technique.

Simple modeling of dipolar coupled 7Li spins and stimulated-echo spectroscopy of single-crystalline β-eucryptite

Abstract Stimulated-echo spectroscopy has recently been applied to study the ultra-slow dynamics of nuclear spin-3/2 probes such as 7 Li and 9 Be in solids. Apart from the dominant first-order quadrupolar interaction in the present article also the impact of the homonuclear dipolar interactions is considered in a simple way: the time evolution of a dipole coupled pair of spins with I =3/2 is calculated in an approximation, which takes into account that the satellite transitions usually do not overlap. Explicit analytical expressions describing various aspects of a coupled quadrupolar pair subjected to a Jeener–Broekaert pulse sequence are derived. Extensions to larger spin systems are also …

Pseudo-stochastic multiple-pulse excitation in dielectric spectroscopy: application to a relaxor ferroelectric

The nonlinear dielectric response of a lead titanate-doped lead magnesium niobate relaxor ferroelectric was studied using pseudo-stochastic binary electrical field excitation. The polarization was recorded for various pulse spacings and electrical field amplitudes. The decay of the field-polarization cross-correlation function could be accelerated by increasing the amplitude of the pulse fields. The extension of these experiments in order to record multidimensional dielectric spectra is illustrated.

Microscopic origin of the nonexponential dynamics in a glassy crystal

The origin of the slow relaxation and of the dynamic heterogeneity is studied for an orientation-ally disordered crystal, orthocarborane, composed of quasi-icosahedrally shaped molecules. Multidimensional deuteron magnetic resonance reveals that large jump angles dominate their complex, anisotropic reorientational motion. It involves a sequence of small-angle tilts about locally preferred axes as well as symmetry adapted threefold jumps. The intrinsic dynamics of this glassy crystal is nonexponential and can be fully accounted for in terms of the tilt and jump motion.

Reorientations and phase transitions in (Kr)1-x(CH4-nDn)x

The condensed isotopic modifications of methane, CH4, CH2D2, and CD4 and their solutions with Kr were investigated using dielectric techniques. The polarizabilities were computed from the permittivities of the pure liquids. Phase diagrams of methane-krypton alloys were deduced in the liquid-solid coexistence region and for the low temperature phases (T&lt;30 K). From the Curielaws, which described the permittivities of the (Kr)1-x(CH2D2)x mixed crystals, the permanent dioole moment of CH2D2 is calculated to be 4 mD. In the octopolar ordered phases of the solid solutions the effective dipole moments are enhanced significantly.

High frequency resistivity in La2-xSrxCu1-yCoyO4 ceramics

Resitivity measurements have been performed in La:Sr:Cu:Co:O ceramics in a frequency range from 5Hz – 10 9 Hz. A strongly frequency dependent resistance has been observed in La 2 CUO 4 which we interpret in terms of a smooth dielectric to metal transition due to localization effects.

Dielectric study of supercooled triphenylphosphite and butyronitrile: Comparison with a mesoscopic model

Abstract Dielectric relaxation has been studied in the supercooled liquids triphenylphosphite (TPP) and butyrontrile (BN). BN is relatively strong according to Angell's classification and can be characterized by a fragility index m = 47. TPP, on the other hand, appears to be the most fragile non-polymeric liquid studied so far (m = 160). The dielectric response of the two glass-formers exhibits different degrees of non-exponentiality which is analyzed in terms of a mesoscopic model of dynamically correlated domains. The relation of this model to the strong versus fragile liquid classification scheme is discussed.

Stimulated-echo NMR spectroscopy of 9Be and 7Li in solids: method and application to ion conductors.

The generation of pure quadrupolar stimulated-echo spectra is successfully demonstrated for the spin-3/2 probe 9Be in a single crystal of triglycine fluoberyllate. This solid exhibits a paraelectric-to-ferroelectric phase transition. From experiments carried out for various mixing times no indications for a slow soft mode could be detected in this crystal. Then ion conducting lithium metal phosphates were studied using 7Li, another spin-3/2 probe which allows for a non-selective excitation of the entire NMR spectrum. In the indium and the scandium phosphates ultra-slow Li hopping processes could be detected directly via the stimulated-echo technique in a time range of up to four orders of m…

Dielectric investigations of pure and mixed fluorocarbons in their condensed phases

We review recent work and present new results on the liquid and solid fluocarbons CMF3 with M = H, F, Cl, Br, CH3, and CF3. The pure compounds as well as several series of binary mixtures were investigated using dielectric measurements. The permittivities of the non-hydrogenatcd non-polar and polar liquids could be described using the Clausius-Mosotti and the Onsager equation, respectively. In CHF3 and C2H3F3 hydrogen bridging leads to deviations from this simple behavior. The trends in the miscibility of four series of fluorocarbon mixtures are in qualitative accord with regular solution theory. The geometrical shapes of the compounds dominate the degrees of order below their melting point…

Nonresonant hole burning spectroscopy of the relaxor ferroelectric PLZT

Abstract The polydispersive dielectric response of a lanthanum-modified lead zirconate titanate relaxor ferroelectric was studied using nonresonant hole burning (NHB) spectroscopy. The dynamic heterogeneity of this material was evidenced by the fact that it was possible to burn frequency-dependent spectral holes. The maximum position of the spectral holes depended on the square root of the pump frequency Ω . The refilling of the spectral holes was monitored subsequent to excitation using various pump frequencies. The refilling data could be collapsed onto a master curve by re-scaling them, again, using Ω −0.5 as scaling factor. The refilling time was found to be much longer than the time sc…

Nonresonant dielectric hole-burning spectroscopy on a titanium-modified lead magnesium niobate ceramic

Nonresonant dielectric hole-burning experiments were performed on the titanium-modified relaxor ferroelectric lead magnesium niobate around the diffuse maximum in the dielectric permittivity. After applying large alternating electric pump fields we monitored the polarization response to small field steps for times between 0.3 ms and 100 s. Depending on the frequency of the pump oscillation a speedup of the polarization response was observed with a maximum located around times corresponding to the inverse pump frequency. The refilling of the dielectric holes was investigated for several temperatures, pump frequencies, and pump field amplitudes. It proceeded always slower than the time scale …

Nonresonant dielectric hole burning spectroscopy of supercooled liquids

The nonexponential response of propylene carbonate and glycerol near their glass transitions could be selectively altered using nonresonant spectral hole burning (NSHB) experiments. This observation provides evidence of the existence of a distribution of relaxation times in these supercooled liquids. NSHB is based on a pump, wait, and probe scheme and uses low-frequency large amplitude electrical fields to modify the dielectric relaxation. The temporal evolution of the polarization of the sample is then measured subsequent to a small voltage step. By variation of a recovery time inserted between pump and probe, the refilling of the spectral features could be monitored and was found to take …