Pronounced Hysteresis Research Articles

Electronic phase separation in multilayer rhombohedral graphite.

Of the two stable forms of graphite, hexagonal and rhombohedral, the former is more common and has been studied extensively. The latter is less stable, which has so far precluded its detailed investigation, despite many theoretical predictions about the abundance of exotic interaction-induced physics1-6. Advances in van der Waals heterostructure technology7 have now allowed us to make high-quality rhombohedral graphite films up to 50 graphene layers thick and study their transport properties. Here we show that the bulk electronic states in such rhombohedral graphite are gapped8 and, at low temperatures, electron transport is dominated by surface states. Because of their proposed topological nature, the surface states are of sufficiently high quality to observe the quantum Hall effect, whereby rhombohedral graphite exhibits phase transitions between a gapless semimetallic phase and a gapped quantum spin Hall phase with giant Berry curvature. We find that an energy gap can also be opened in the surface states by breaking their inversion symmetry by applying a perpendicular electric field. Moreover, in rhombohedral graphite thinner than fournanometres, a gap is present even without an external electric field. This spontaneous gap opening shows pronounced hysteresis and other signatures characteristic of electronic phase separation, which we attribute to emergence of strongly correlated electronic surface states.

Microscopic mechanism of thermomagnetic instabilities in type-II superconducting thin films under AC magnetic fields

Thermomagnetic instability is one of the significant challenges for the application of superconducting devices. In this paper, the microscopic mechanism of thermomagnetic instability in superconducting films subjected to a transient AC magnetic field is numerically investigated by coupling the generalized time dependent Ginzburg–Landau equations and the heat diffusion equation. The influences of magnetic field ramp rate, ambient temperature, and nanometer-sized artificial pinning on the vortex matter are considered in our simulations. It has been found that vortex alignment and repulsion play significant roles in the branching of the penetration trajectories of the magnetic flux. Under fast ramping magnetic fields, the increase in the temperature and instability in the vortex matter are more significant. However, the rising temperature and jump size in the magnetization weaken as the ambient temperature increases. Pronounced hysteresis in the vortex dynamics has been found in the film subjected to AC magnetic fields. As the AC cycle proceeds, the vortex penetration process gets more unstable. We have also found that the nanometer sized pinning strongly modulates the penetration of vortices and the vortex matter is highly correlated with the lattice structure of the pinning sites. Our results provide new insights into vortex dynamics and give a mesoscopic understanding on the channeling and branching in the vortex penetration paths in superconductors under AC magnetic fields.

Theoretical investigation of a miniature microwave driven plasma jet

Radio frequency driven plasma jets are compact plasma sources which are used in many advanced fields such as surface engineering or biomedicine. The MMWICP (miniature micro wave ICP) is a particular variant of that device class. Unlike other plasma jets which employ capacitive coupling, the MMWICP uses the induction principle. The jet is integrated into a miniature cavity structure which realizes an LC-resonator with a high quality factor. When excited at its resonance frequency, the resonator develops a high internal current which—transferred to the plasma via induction—provides an efficient source of RF power. This work presents a theoretical model of the MMWICP. The possible operation points of the device are analyzed. Two different regimes can be identified, the capacitive E-mode with a plasma density of ne ≈ 5 × 1017 m−3, and the inductive H-mode with densities of ne ⩾ 1019 m−3. The E to H transition shows a pronounced hysteresis behavior.

Ferrocene on Insulator: Silane Coupling to a SiO2 Surface and Influence on Electrical Transport at a Buried Interface with an Organic Semiconductor Layer.

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO2/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO2/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO2 layer. The FcSi on SiO2/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO2/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO2 surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

Large Wiedemann effect in a magnetoactive elastomer

Large twists of a soft tube (hollow cylinder) in helical magnetic fields are presented for the first time. Such a phenomenon is usually denoted as the Wiedemann effect. The tube is fabricated from a soft magnetoactive elastomer material with the shear modulus of about 56 kPa. The composite material comprises 80 mass% of micrometer-sized iron particles embedded into a polydimethylsiloxane matrix. The circular magnetic field is generated by an electric current in a straight wire passing through the inner hole of the tube. The maximum value of approximately 350″/cm is observed in a longitudinal magnetic field of a few kA/m overlapped with a circumferential magnetic field of about 1.4 kA/m on the surface of the inner hole. A pronounced hysteresis in the dependence of the Wiedemann effect on the circular magnetic field is found. The ways to enhance the Wiedemann twist in magnetoactive elastomers are discussed. The observed large effect is promising for application in magnetic-field controlled torsional actuators, in particular for soft robotics.

Enabling room temperature ferromagnetism in monolayer MoS2 via in situ iron-doping

Two-dimensional semiconductors, including transition metal dichalcogenides, are of interest in electronics and photonics but remain nonmagnetic in their intrinsic form. Previous efforts to form two-dimensional dilute magnetic semiconductors utilized extrinsic doping techniques or bulk crystal growth, detrimentally affecting uniformity, scalability, or Curie temperature. Here, we demonstrate an in situ substitutional doping of Fe atoms into MoS2 monolayers in the chemical vapor deposition growth. The iron atoms substitute molybdenum sites in MoS2 crystals, as confirmed by transmission electron microscopy and Raman signatures. We uncover an Fe-related spectral transition of Fe:MoS2 monolayers that appears at 2.28 eV above the pristine bandgap and displays pronounced ferromagnetic hysteresis. The microscopic origin is further corroborated by density functional theory calculations of dipole-allowed transitions in Fe:MoS2. Using spatially integrating magnetization measurements and spatially resolving nitrogen-vacancy center magnetometry, we show that Fe:MoS2 monolayers remain magnetized even at ambient conditions, manifesting ferromagnetism at room temperature.

Phase transitions in bulk and confined organic ferroelectric DIPAI

We studied phase transitions in new organic ferroelectric DIPAI embedded into porous alumina and in bulk DIPAI. Complex permittivity and third harmonic generation coefficient were measured within a wide temperature range. The increase in the third harmonic generation indicates the emergence of the polar phase. Two phase transitions were seen in bulk DIPAI upon heating from room temperature after preliminary heating up to 420 K while only a transition was found upon cooling accompanied with pronounced thermal hysteresis. The ferroelectric phase was observed in the range between two transitions upon heating and below the transition upon cooling. In contrast, two phase transitions occur in DIPAI confined to porous alumina upon heating and cooling. The transitions do not show noticeable thermal hysteresis. It was suggested that different behavior of bulk and confined DIPAI results from slow kinetics of phase transitions in bulk upon cooling. The noticeable shift of the transition temperatures for DIPAI within alumina pores of different diameters was treated using the theories of size effects in ferroelectrics.

Non-Isothermal Kinetics of Kr Adsorption by Nanoporous γ-Mg(BH4)2 from in Situ Synchrotron Powder Diffraction.

Crystalline materials with pore dimensions comparable to the kinetic diameters of the guest molecules are attractive for their potential use in adsorption and separation applications. The nanoporous γ-Mg(BH4)2 features one-dimensional channels matching this criterion for Kr uptake, which has been probed using synchrotron powder diffraction at various pressures and temperatures. It results in two coexisting crystalline phases with the limiting composition Mg(BH4)2·0.66Kr expecting the highest Kr content (50.7 wt % in the crystalline phase) reported for porous materials. Quasi-equilibrium isobars built from Rietveld refinements of Kr site occupancies were rationalized with a noncooperative lattice gas model, yielding the values of the thermodynamic parameters. The latter were independently confirmed from Kr fluorescence. We have also parameterized the pronounced kinetic hysteresis with a modified mean-field model adopted for the Arrhenius kinetics.

Magnetic Structured Nickel Core-Shell @ Silica/PMMA Nanocomposites from Synthesis to Applications

Incorporating Ni@SiO2 nanoparticles on poly-methyl methacrylate (PMMA) can alter electrical, optical, and magnetic properties of Ni nanoparticles to be used for energy storage applications, photo electronic devices and spintronic applications. The Ni@SiO2/PMMA nanocomposite samples are prepared by casting method. The morphology of the prepared nanoparticles was examined through high resolution transition electron microscope revealed the formation of SiO2 coating on ni nanoparticles. Furthermore, the topography of nanocomposites was characterized by the field emission scanning electron microscope. We investigated the formation of crystalline phase of Ni nanoparticles through X-ray diffraction. The Complex dielectric permittivity, electrical conductivity, electric modulus and impedance spectra of the PNC films were investigated in the frequency range from 0.1 Hz to 10 MHz. The real and imaginary parts of the permittivity decrease with increasing frequency due to an increase in Ni@SiO2 content. All the nanocomposites showed relatively low conductivity values and high impedance that could be used for nano-dielectrics. UV–Vis spectrophotometer was used to measure optical properties such as transmittance, and absorbance at normal incidence in the wavelength range of 200–1100 nm. The transmittance was found to decrease while the absorbance increases with increasing Ni@SiO2 nanoparticles. The indirect optical band gap of the composite films was calculated, and it was sharply decreased. Magnetic hysteresis plots at room temperature of composites Ni@SiO2/PMMA were studied. All samples demonstrate ferromagnetic behavior with well pronounced magnetic hysteresis.

A phenomenological model for the inelastic stress–strain response of a potato tuber

In this article, we synthesise concepts from the theories of plasticity, volumetric growth, and pseudo-hyperelasticity to develop a phenomenological constitutive model for potato tuber tissue. Here, particular focus is laid on the inhomogeneity of the constitutive behaviour across different anatomical zones of a potato tuber. The internal stresses are expressed in terms of an elastic contribution to the local strains and are controlled by a kinetic memory variable that traces the past strain history. Inelastic strains, by contrast, are considered as a combination of a plastic component and a pure volumetric component mimicking the eviction of fluid. Considering tubers of cultivar Belana, we identify the relevant constitutive parameters based on stress–stretch curves obtained from single-cycle uniaxial compression experiments on samples extracted from different anatomical tuber parts. The stress–strain response of the tissue is characterised by a pronounced and well-reproducible hysteresis which displays slight stiffening along the initial loading branch. Considering the parenchyma microstructure, the significant reduction in tissue turgidity on unloading may be caused by the eviction of intracellular fluid from the parenchyma cells and an inelastic cell wall response. The experiments show that the inelastic volume change varies approximately linearly with the axial stretch. Additionally, histological analyses are presented in an attempt to quantify microstructural inhomogeneities.

Microstructure of Compacted Loess and Its Influence on the Soil‐Water Characteristic Curve

Soil‐water characteristic curve (SWCC) is a key constitutive relationship for studying unsaturated soil, and as is known, microstructure of the soil has great influence on the mechanical behaviour of the soil. In this study, the wetting and drying soil‐water characteristic curves (SWCCs) of loess compacted at three different water contents were measured using the filter paper method. And microproperties of compacted loess were obtained by the mercury intrusion method (MIP) and scanning electron microscope (SEM). Results show that the compaction water contents have significant influence on the SWCC and microstructure. The pore size distribution (PSD) curves have great differences in macropore range and are similar in micropore range. Loess compacted at optimum and dry of optimum are generally connected, while there are certain number of nonintruded pores in loess compacted at wet of optimum. The SWCC curves vary significantly in low suction (ua − uw < 1000 kPa) and tend to converge together in high suction (ua − uw ≥ 1000 kPa). Hysteresis in the SWCCs is more obvious for loess compacted at optimum and dry of optimum in the matric suction of 0∼100 kPa; however, there is a pronounced hysteresis for loess compacted at wet of optimum in full matric suction range. The characteristic of the SWCCs including their hysteresis can be well interpreted from the loess microstructure.

Thorough wetting and drainage of a peat lysimeter in a climate change scenario

AbstractA peat deposit (Zennare basin, Venice coastland, Italy) was monitored in previous field studies to investigate the hydrological response of organic soil to meteorological dynamics. Field tests and modelling predictions highlighted the risk of the complete loss of this peat layer during the next 50 years, due to oxidation enhanced by the increased frequency of warmer periods. Unfortunately, despite the considerable impacts that are expected to affect peat bogs (in this area and worldwide), only a few experimental studies have been carried out to assess the hydrologic response of peat to severe water scarcity. Because of that, an undisturbed 0.7 m3 peat monolith was collected, transferred to the laboratory and instrumented. The total weight (representative of the water content dynamics of the peat monolith as a whole), and two vertical profiles of matric potentials and water content were monitored in controlled water‐scarce conditions. After an extended air‐drying period, the monolith was used as an undisturbed peat lysimeter and a complete cycle of wetting and drainage was performed. Supplementary measurements of matric potential ψ and water content θ were collected by testing peat subsamples on a suction table apparatus. A set of water retention curves was determined in a range of matric potentials broader (ψ down to −7 m) than the current natural conditions in the field (minimum ψ = −1 m). While water content at saturation showed values similar to those in the original natural conditions (θ ≅ 0.8), a remarkable loss of water holding capacity (even for low potentials) has been highlighted, especially in deep layers that are now permanently below the water table. The retention curves changed shape and values, with a more pronounced hysteresis visible in an increasing distance between wetting and drying data. Hydraulic non‐equilibrium between the water content and water potential could be a possible cause and it is worth modelling in future studies. The parameters of the van Genuchten retention curves were obtained for the wetting and the drying phases.

Low-Voltage Organic Nonvolatile Memory Transistors with Water-Soluble Polymers Containing Thermally Induced Radical Dipoles.

A water-soluble acidic polymer, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), was applied as a gate-insulating layer for organic field-effect transistors (OFETs). Before depositing the poly(3-hexylthiophene) (P3HT) channel layers, the PAMPSA layers were subjected to thermal treatment at various temperatures from 140 to 230 °C. The OFET performance was greatly enhanced by thermal treatment between 140 and 170 °C, whereas it became very poor at higher temperatures (200-230 °C). In particular, the transfer curves showed pronounced hysteresis phenomena at 170 °C. Various measurements including thermogravimetric analysis and X-ray photoelectron spectroscopy disclosed that the PAMPSA chains underwent thermal degradation from ca. 160 °C and could generate carbon radicals leading to the formation of dipoles with the nitrogen lone pair electrons. The carbon-nitrogen dipoles delivered hysteresis phenomena to the OFETs with the PAMPSA layers treated at 170 °C, which exhibited excellent memory retention characteristics up to 10 000 cycles even at -1 V. Hence, it is expected that the thermally treated PAMPSA layers can be used as one of the viable gate-insulating memory materials for low-voltage transistor-type organic memory devices (TOMDs).

Soybean Hull Insoluble Polysaccharides: Improvements of Its Physicochemical Properties Through High Pressure Homogenization

Soybean hull is an agroindustrial waste which has not been fully studied as a food ingredient. The aims of this work were to obtain insoluble fibers from soybean hull and to evaluate the effect of high pressure homogenization (HPH) on its physicochemical properties. Hull insoluble polysaccharides (HIPS) were obtained in a single step, as the insoluble residue after pectin removal. FTIR showed bands corresponding to cellulose and hemicellulose in HIPS, and thermogravimetric analysis showed two degradation events at 236.3 °C and 325.6 °C, corresponding to cellulose and hemicellulose, respectively. HIPS dispersions (pH 3.00) were subjected to HPH by three cycles at increasing pressures (up to 1000 bar), obtaining soybean hull nanofibers. SEM images show that HPH at 1000 bar reduced the dimensions of the fiber bundle from 30 to 90 μm in length and 9–15 μm in diameter to nanofibers of 10–30 μm in length and 100–400 nm in diameter. AFM further confirms a heterogeneous distribution of sizes in HIPS800 and HIPS1000, evidencing the presence of individual nanofibers with diameters around 50 ± 10 nm and 40 ± 10 nm, respectively, with several μm in length. Furthermore, an increase in water holding capacity from 2.1 to 61 gwater/gdry matter and viscosity from 0.39 to 34,945 Pa.s were achieved as HPH at 1000 bar treatment was applied. HPH increased the interfacial area and promoted the interconnection of fibers in a hydrated gel-like structure. This explains flow behavior, which was extensively studied in this work: three-region viscosity profile (shear-thinning, plateau or shear-thickening and shear-thinning) and a pronounced hysteresis loop. Oscillatory rheology was used to study the viscoelastic behavior of HIPS dispersions. HIPS are a source of nanofibers, easy to obtain through a single step of chemical treatment followed by the application of high pressures. It is remarkable that the use of few chemical solvents is favorable from an environmental point of view. This work also suggests a potential application of HIPS to improve physicochemical and structural properties in acidic foods.

The Thermal Unbalance Effect Induced by a Journal Bearing in Rigid and Flexible Rotors: Experimental Analysis

The present work presents the experimental analyses of a rigid (short) and a flexible (long) rotor subject to thermal unbalance effects. The rotors are supported by a ball bearing and by a cylindrical journal bearing. The differential heating generated in the journal bearing is responsible for the thermal unbalance. The results obtained with the short rotor at 7 krpm showed an increase in the synchronous amplitudes but slight phase changes before stabilization. The pronounced hysteresis of the synchronous amplitudes obtained during coast-down proved that the amplitude increase is due to the thermal unbalance. The results obtained for the long rotor at 6.6 krpm showed the same stabilized response when start-up was performed in 180 s. However, an instability leading to journal bearing contact was triggered when the start-up time was decreased to 80 s. The presented experimental results are the synchronous amplitudes and phases, the mean temperatures, and the maximum temperature differences of the journal and of the bearing and the phase lags between the high spot and the hot spot.

Thermally Induced Spin Transition in a 2D Ferrous Nitroprusside

This study reports the intercalation of pyridine molecules between neighboring layers of two‐dimensional (2D) ferrous nitroprusside. In the material under study, the stacking of neighboring layers results in the formation of a long range ordered solid, where the 3D structure is supported by dipole‐dipole attractive interactions between neighboring pyridine molecules in the interlayer region. No chemical interactions were observed between layers, which preserve their identity as a 2D material. In this hybrid inorganic–organic solid, a thermal induced spin transitions from high to low spin on cooling and then from low to high spin on heating were observed. Such thermal induced spin crossover transition takes place with a pronounced hysteresis of 18 K, according to the magnetic and DSC measurements. That spin crossover transition is characterized by an extremely small structural change, involved a unit cell volume reduction from the high to low spin states of only 0.7 % and a related Fe–NPyridine distance shortening of 0.10 Å. The two spin states and the transition between them were additionally characterized from magnetic and DSC data and, Raman and Mössbauer spectra.

Possible manifestations of the chiral anomaly and evidence for a magnetic field induced topological phase transition in the type-I Weyl semimetal TaAs

We evaluate the topological character of TaAs through a detailed study of the angular, magnetic-field and temperature dependence of its magnetoresistivity and Hall-effect(s), and of its bulk electronic structure through quantum oscillatory phenomena. At low temperatures, and for fields perpendicular to the electrical current, we extract an extremely large Hall angle $\Theta_H$ at higher fields, that is $\Theta_H \sim 82.5^{\circ}$, implying a very pronounced Hall signal superimposed into its magnetoresistivity. For magnetic fields and electrical currents perpendicular to the \emph{c}-axis we observe a very pronounced planar Hall-effect, when the magnetic field is rotated within the basal plane. This effect is observed even at higher temperatures, i.e. as high as $T = 100$ K, and predicted recently to result from the chiral anomaly among Weyl points. Superimposed onto this planar Hall, which is an even function of the field, we observe an anomalous planar Hall-signal akin to the one reported for that is an odd function of the field. Below 100 K, negative longitudinal magnetoresistivity (LMR), initially ascribed to the chiral anomaly and subsequently to current inhomogeneities, is observed in samples having different geometries and contact configurations, once the large Hall signal is subtracted. Our measurements reveal a phase transition upon approaching the quantum limit that leads to the reconstruction of the FS and to the concomitant suppression of the negative LMR indicating that it is intrinsically associated with the Weyl dispersion at the Fermi level. For fields along the \emph{a}-axis it also leads to a pronounced hysteresis pointing to a field-induced electronic phase-transition. This collection of unconventional tranport observations points to the prominent role played by the axial anomaly among Weyl nodes.

Deformed lying helix transition and lasing effect in cholesteric LC layers at spatially periodic boundary conditions

ABSTRACTThe field-induced orientational transition in layers of cholesteric liquid crystals with spatially periodic modulation of the surface anchoring is studied by numerical simulations and experimentally. The modulation of the surface anchoring is implemented using high-resolution focused ion-beam treatment of a polymer film providing planar alignment conditions. A specific feature of the orientational transition is that the thermodynamically stable initial planar structure with the helix axis along the normal to the layer transforms under an electric field into an equilibrium structure with a deformed lying helix (DLH) in the plane of the layer. For such a transition to occur the natural pitch of the cholesteric helix must be substantially less than the anchoring modulation period. The appearance of the DLH with a pitch corresponding to the anchoring modulation period results in strongly enhanced first-order diffraction efficiency. The orientational DLH transition is characterised by a rather narrow driving voltage range with a pronounced hysteresis. The waveguide lasing effect with characteristic of the deformed helix spectral modes is demonstrated in a range of the DLH transition.

Lattice Parameter Hysteresis in Li- and Mn-Rich Layered Oxides and Its Dependence on State of Charge and Open Circuit Voltage

Li- and Mn-rich layered oxides, also known as high energy NCM (HE-NCM, Li1+x[NiCoMn]1-xO2 with typically 0.1 < x < 0.2), are promising next-generation cathode active materials (CAMs) for Li-ion batteries, since they contain intrinsically more lithium ions than regular NCM materials (x < 0.05). The gain in capacity is accompanied by the drawbacks of voltage hysteresis (between charge and discharge) and voltage fade (during long-term cycling).1 The voltage hysteresis is a unique property of over-lithiated layered oxides, which does not only manifest itself in the voltage profile, but also in the cathode resistance,2 the redox activity of transition metals (TM) and oxygen,2 and the bond distances.3 Figure 1 shows our results of an in-situ X-ray diffraction (XRD) experiment during the initial cycles of a Li-rich NCM material. As seen in Figure 1a and b, the state of charge (SOC, equivalent to total xLi) dependence of the bulk lattice parameters a and c after the first activation cycle is characterized by a pronounced hysteresis between charge and discharge. Here, the hysteresis loop of the lattice parameter a is clearly different from that of c. Furthermore, the hysteresis of the lattice parameter a vanishes when it is correlated to the open circuit voltage (OCV) of the respective SOC (see Figure 1c), but c maintains the shifted maxima during charge and discharge (see Figure 1d). Based on the literature, these observations could be either explained by a path dependency of the reversible TM migration between TM and Li layer,4 the oxygen redox,2 or a combination of both.5 In addition to in-situ XRD data, we will show co-refined X-ray and neutron diffraction data of selected ex-situ samples, which have either the same SOC or OCV. By means of diffraction techniques, it is our goal to elucidate the lattice parameter variations in Li-rich CAMs and to clarify the often described contribution of TM migration to the hysteresis effects. Figure 1: In-situ XRD measurement of HE-NCM during the first 3 cycles. The pouch cell was cycled at a rate of C/10 between 2.0-4.8 V against metallic lithium with intermediate OCV steps to collect XRD patterns (at a laboratory diffractometer with Mo-Kα1 radiation). Using the trigonal model (space group R-3m), the lattice parameters a and c are shown as a function of SOC (a,b) and OCV (c,d), respectively. Acknowledgements: We want to acknowledge BASF SE for the support within the frame of its scientific network on electrochemistry and batteries and the BMBF (Federal Ministry of Education and Research, Germany) for its financial support within the ExZellTUM II project (grant number 03XP0081). We also thank the research neutron source FRM II for access to the instrument SPODI.

Peculiarities of melting and crystallization of n-decane in a porous glass

Melting and crystallization of n-decane embedded into porous glass with the mean pore size of about 6.4 nm were studied using acoustic and DSC methods. Smearing of the phase transitions, decrease of melting and freezing temperatures, pronounced hysteresis between melting and crystallization were revealed by both methods. In DSC measurements for the pore filling factors 70% and higher double peaks were observed upon cooling while only single peaks were present upon heating. Also a high reduction of the corresponding phase transition heats was revealed. Melting and freezing intervals determined by acoustic and DSC methods strongly differed from each other. A model which qualitatively explains the observed anomalies is proposed. It supposes the formation of liquid layers on the surface of the pores.