Meyer-Neldel Rule Research Articles

Robust theory of thermal activation in magnetic systems with Gilbert damping

Magnetic systems can exhibit thermally activated transitions whose timescales are often described by an Arrhenius law. However, robust predictions of such timescales are only available for certain cases. Inspired by the harmonic theory of Langer, we derive a general activation rate for multidimensional spin systems. Assuming local thermal equilibrium in the initial minimum and deriving an expression for the flow of probability density along the unstable dynamical mode at the saddle point, we obtain the expression for the activation rate that is a function of the Gilbert damping parameter, α. We find that this expression remains valid for the physically relevant regime of α≪1. When the activation is characterized by a coherent reorientation of all spins, we gain insight into the prefactor of the Arrhenius law by writing it in terms of spin wave frequencies and, for the case of a finite spin chain, obtain an expression that depends exponentially on the square of the system size indicating a break-down of the Meyer-Neldel rule. Published by the American Physical Society 2024

Electrical Conduction Mechanism of Mg-Doped ZrO2 Thin Films.

Amorphous ZrO2 thin films with increasing Mg content were deposited on quartz substrates, by dip coating method. The films are transparent in the visible domain and absorbent in UV, with an optical band gap that decreases with the increase of Mg content, from 5.42 eV to 4.12 eV. The temperature dependent conductivity measurements showed typical semiconductor comportment. The decrease of the electrical conductivity by Mg doping was related to the increase of the OH groups (37% to 63%) as seen from X-ray Photoelectron Spectroscopy. It was found out that the electrical conductivity obeys the Meyer-Neldel rule. This rule, previously reported for different disordered material systems is obtained for ZrO2 for the first time in the literature. Exploring novel aspects of Mg-doped ZrO2, the present study underscores the origin of the Meyer-Neldel rule explained by the small-polaron hopping model in the non-adiabatic hopping regime. Determination of the presence of such a conduction mechanism in the samples hold promise for comprehending the important aspects, which might be a concern in developing various devices based on Mg-doped ZrO2.

Observation of temperature-dependent capture cross section for main deep-levels in β-Ga2O3

Direct observation of the capture cross section is challenging due to the need for extremely short filling pulses in the two-gate Deep-Level Transient Spectroscopy (DLTS). Simple estimation of the cross section can be done from DLTS and admittance spectroscopy data but it is not feasible to distinguish temperature dependence of pre-exponential and exponential parts of the emission rate equation with sufficient precision conducting a single experiment. This paper presents experimental data of deep levels in β-Ga2O3 that has been gathered by our group since 2017. Based on the gathered data, we propose a derivation of apparent activation energy (Eam) and capture cross section (σnm) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between Eam and σnm according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C0 and C1 as well as capture barrier Eb. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σn are overestimated by 1–3 orders of magnitude. A careful consideration of the data also allows to be more certain identifying deep levels by their “fingerprints” (Ea and σn) considering two additional parameters (EMN and σ00) and to verify the density functional theory computation of deep-level recombination properties.

Low-temperature electrical conductivity of ion-beam irradiated Bi–Sb films

Bismuth-antimony alloys are among the most studied topological insulators and also have very promising thermoelectric properties. In addition, in the amorphous state they exhibit superconductivity with critical temperatures in the range 6.0–6.4 K. In this work, we have prepared and studied different polycrystalline films of Bi100–xSbx (x = 0, 5, 10, 15), and we have induced, through ion beam irradiation, significant damage in their internal structure with the aim of amorphizing the material. Specifically, we have irradiated Bi ions in the 10–30 MeV range, exploiting the capabilities of a 5 MV ion beam accelerator of tandem type. We have characterized the Bi–Sb films before and after irradiation from a morphological and structural point of view and measured their electrical resistivity from room temperature to near 2 K, to evaluate the influence of the preparation method and degree of disorder. We have found that the studied Bi–Sb system always behaves as a small energy gap semiconductor that follows the empirical Meyer–Neldel rule, which correlates the conductivity prefactor with the exponential value of the energy gap.

Empirical universal approach to describing the thermal conductivity of amorphous polymers: Effects of pressure, radiation and the Meyer–Neldel rule

In this study, we propose and validate a universal temperature-dependent model for characterizing the thermal conductivity of amorphous polymers over a wide temperature range. Our approach captures key features in the thermal conductivity data, including a plateau, an inflection point, and the subsequent increase and saturation with rising temperature. Importantly, this model proves effective not only for pristine amorphous polymers but also for polymers subjected to external influences. We investigate the temperature-dependent thermal conductivity of amorphous polymer materials under various external conditions, such as hydrostatic pressure, radiation exposure, and the incorporation of fillers. Our analysis reveals novel insights into the dual-channel heat transfer mechanisms within amorphous polymers. Specifically, we observe a linear relationship between the logarithm of the “coherence” conductivity pre-factor and the characteristic energy, consistent with the Meyer–Neldel rule governing thermal conductivity. This research advances our understanding of thermal transport in amorphous polymers and underscores the applicability of the proposed universal model in describing complex thermal behavior across different conditions.

Exploring dielectric and AC conduction characteristics in elemental selenium glass modified with silver halides.

In this research work, we have examined the influence of silver halide doping on the dielectric dispersion and AC conduction of elemental selenium. The in-depth investigation shows that when the dopant silver halides are incorporated, there are noticeable changes in the parent selenium's dielectric constant (ε'), dielectric loss (ε''), and AC conductivity (σ ac). When we frame the discussion of the obtained results with the relevant transport models, we found that in pure selenium and Se95(AgI)5, conduction is primarily due to polaron hopping and follows the correlated barrier hopping (CBH) model. In contrast, Se95(AgBr)5 predominantly exhibits non-overlapping small polaron tunneling (NSPT). Interestingly, Se95(AgCl)5 demonstrates both NSPT and CBH conduction mechanisms, depending on the temperature range: NSPT is dominant between 303 K and 313 K, while CBH prevails from 318 K to 338 K. Additionally, our findings revealed the presence of both the Meyer-Neldel rule (MNR) and its reverse in the prepared silver halide chalcogenide alloys. The best optimization of dielectric constant and loss is observed for silver iodide as compared to silver chloride and silver bromide. Comparison with other silver-containing chalcogenide glasses indicates the better dielectric performance of the present silver halides containing selenium.

Entropy and Isokinetic Temperature in Fast Ion Transport.

Ion transport in crystalline solids is an essential process for many electrochemical energy converters such as solid-state batteries and fuel cells. Empirical data have shown that ion transport in crystal lattices obeys the Meyer-Neldel Rule (MNR). For similar, closely related materials, when the material properties are changed by doping or by strain, the measured ionic conductivities showing different activation energies intersect on the Arrhenius plot, at an isokinetic temperature. Therefore, the isokinetic temperature is a critical parameter for improving the ionic conductivity. However, a comprehensive understanding of the fundamental mechanism of MNR in ion transport is lacking. Here the physical significance and applicability of MNR is discussed, that is, of activation entropy-enthalpy compensation, in crystalline fast ionic conductors, and the methods for determining the isokinetic temperature. Lattice vibrations provide the excitation energy for the ions to overcome the activation barrier. The multi-excitation entropy model suggests that isokinetic temperature can be tuned by modulating the excitation phonon frequency. The relationship between isokinetic temperature and isokinetic prefactor can provide information concerning conductivity mechanisms. The need to effectively determine the isokinetic temperature for accelerating the design of new fast ionic conductors with high conductivity is highlighted.

Structural Study, Observation of Non-Ohmic I–V Characteristics and Analysis of Meyer–Neldel Rule in Sb-Additive Se-Te-Ge Quaternary Amorphous Alloys

Structural Study, Observation of Non-Ohmic I–V Characteristics and Analysis of Meyer–Neldel Rule in Sb-Additive Se-Te-Ge Quaternary Amorphous Alloys

THE STRUCTURAL AND ELECTRICAL PROPERTIES OF NON-STOICHIOMETRIC CADMIUM SELENIDE THIN FILMS

Non-stoichiometric CdxSe100-x (x=10, 20, 30 at. %) alloys were prepared by melt-quenching technique, while thin films of these alloys were prepared by vacuum thermal evaporation technique. The Differential thermal analysis (DTA) results showed that the composition affects the characteristic temperatures, for instance, the glass transition, and peak crystallization temperatures. X-ray diffraction patterns (XRD) of the as-deposited films confirmed its amorphous nature except for films with x=30 at. %. These results were confirmed by scanning electron microscopy (SEM) investigations and correlated to the rigidity percolation threshold of the lattice. Furthermore, XRD patterns indicated that amorphous structures transformed into crystalline structures for annealed thin films at 423 K for 30 minutes. The microstructure parameters (crystal size, microstrain, and dislocation density) of both Se and CdSe phases were calculated for annealed films. The temperature dependence of dark d.c. conductivity of thin films was studied in the temperature range (300-500 K). The electrical measurements results showed two types of conduction mechanisms. Conduction is due to extended state in the temperature range (370-500 K) and variable range hopping in the temperature range (300-370 K). Moreover, in the high temperature range, the results indicate the validity of Meyer-Neldel rule (MNR) in the studied samples.

Thermal behavior of E′ point defects in gamma-irradiated natural quartz: Study of the Meyer-Neldel rule using electron spin resonance

We examined the thermal characteristics of the E' (E′1) center in gamma-ray irradiated natural quartz using electron spin resonance (ESR) spectroscopy. Assuming first order kinetics, we suggested a mechanism and, consequently, an analytical model to explain the thermal evolution of the effective concentration of E′ point defect. The model was used to track the ESR evolution of E′ centers signal while taking into account the existence of two independent types of E′ centers. The kinetic characteristics (activation energy and frequency factor) of both E′ centers were found to be slightly different. The activation energies of thermal production and annihilation of these two centers were shown to be different from process to another and to be linearly dependent on their associated frequency factors in respect to the accumulated gamma-dose, following the Meyer-Neldel rule. As a result, one of the two E′ is shown to have been irradiation-annihilated like center, while the other is found to have been irradiation-induced like center.

Impedance spectroscopy and conduction mechanism analysis of bulk nanostructure Prussian blue pellets

The structure and morphology of the fabricated Prussian Blue (PB) pellets are examined using FTIR, XPS, XRD and FESEM techniques. The morphology of the crystalline Prussian blue (PB) revealed a nanostructure with an average crystallite size of 91 nm. The frequency (42 Hz–1 MHz) and temperature (303–393K) of the Prussian Blue (PB) in Bulk form are dependent. In the medium region (1 kHz–100 kHz), the electric dipoles relax and start to lag the applied ac electric field signal and the estimated activation energy of 0.247 eV. The investigated Nyquist plots (Z″ versus Z′) of the Prussian Blue (PB) samples at different temperatures (303–393 K) are interpreted by an equivalent parallel RgCg circuit. The bulk resistance of Prussian Blue samples was estimated at various temperatures, and its behaviour exhibited temperature dependence; generally, it follows the Nearest Neighbor Hopping (NNH) model. According to Meyer–Neldel rule, the calculated activation energy is 0.565 ± 0.001 eV. The evidence of localized states is investigated, and its density, N(EF) ∼ 5.47 × 1018 eV−1 cm−3. The ac conductivity, σac, merges into a plateau of two parts: the first is a frequency-independent dc conductivity, σdc, which is strongly temperature-dependent. The rest of the plateau at higher frequencies showed the temperature-insensitive ac conductivity obeying Jonscher's power law. The values of the exponent s were investigated to figure out the intimate conduction mechanism in Prussian Blue (PB) samples; it follows the correlated barrier hopping (CBH) theoretical model. The hopping distance and energy have values ∼ unity and ≥ kBT, respectively. The experimental results revealed a linear relationship between hopping distance and energy against temperature, with the first decreasing and the second increasing linearly.

Comparative study of the exponential-trap-based and the mobility-based space-charge-limited current models for organic diode modeling

Current model is presented for the forward-biased organic diodes. Generally, the diode current consists of two parts: the space-charge-limited current in high-voltage regime and the Ohmic current in low-voltage regime. The two classical space-charge-limited current models, i.e., the exponential-trap-based model and the mobility-based model, are analyzed. Their similarity and difference are clarified: they are similar in the form of the Meyer–Neldel rule, but different in the diode thickness. Comparing their calculated results with the available experimental data at different thicknesses, it is found that, the exponential-trap-based model is suitable, and the mobility-based model shows limitation. Moreover, the Ohmic current model is presented considering the temperature and thickness dependence. Combining the exponential-trap-based space-charge-limited current model with the Ohmic current model, the diode current model is achieved. The model is analytical and suitable for circuit simulation, and is verified by the available experimental data at different temperatures and thicknesses.

Electronic transport properties of Ti-supersaturated Si processed by rapid thermal annealing or pulsed-laser melting

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work.

Thermodynamic Interpretation of the Meyer-Neldel Rule Explains Temperature Dependence of Ion Diffusion in Silicate Glass.

We study the temperature-dependent diffusion of many types of metal and semimetal ions in soda-lime glass using thermal relaxation ion spectroscopy, a technique that provides an electrical readout of thermally activated diffusion of charge carriers driven by built-in concentration gradients and electric fields. We measure the temperature of the onset of the motion, relevant to the long term storage of radioactive elements. We demonstrate the unique behavior of silver in soda-lime glass, enabling a thermal battery with rapid discharge of stored energy above a threshold temperature. We show that the Meyer-Neldel rule applies when comparisons of temperature-dependent diffusion rates are made between related measurements on one sample or between the same measurements on related samples. The results support a thermodynamic interpretation of the Meyer-Neldel rule as an enthalpy-entropy correlation where the Meyer-Neldel temperature (T_{MN}) is the temperature that enables liquidlike, barrier-free motion of the ions, with an upper limit set by the melting point of the host medium. This interpretation explains the observed reduction in T_{MN} by built-in electric fields in depletion layers and why the upper limit for T_{MN} for all ions is set by the glass transition temperature.

Highly conducting nanophases of Ag2S–Se-Ge chalcogenide glassy systems: Explanations via computational descriptions

The temperature and frequency dependent AC conductivity of some Ag2S doped chalcogenides is prepared in the laboratory and experimental data have been collected. Its structural analysis is carried out with X-Ray Diffraction and UV–Vis Spectroscopic methods. The estimated values of optical band gap energy, Egare found to increase with Ag2S content and the present system may be classified as allowed indirect band gap semiconductor. The density and molar volume of as-prepared samples have also been estimated. The AC conductivity of this system has been found to obey the Meyer-Neldel (MN) rule. The decrease of Meyer-Neldel characteristic energy EMN with compositions has been observed. Higher conductivity as well as hopping frequency should be caused due to highly conducting Ag2Senanophases, which is confirmed from DFT and Density of States (DOS) spectra.

On the Study of “Further Meyer–Neldel Rule” in Thermally Activated High Field Conduction of Se-Te-Pb Glassy Alloys

On the Study of “Further Meyer–Neldel Rule” in Thermally Activated High Field Conduction of Se-Te-Pb Glassy Alloys

Optimizing the Proton Conductivity with the Isokinetic Temperature in Perovskite‐Type Proton Conductors According to Meyer–Neldel Rule

AbstractPerovskite‐type metal oxides such as Y‐doped BaMO3 (M = Zr/Ce) have drawn considerable attention as proton‐conducting electrolytes for intermediate temperature ceramic electrochemical cells. Improving the proton conductivity at lower temperatures requires a comprehensive understanding of the proton conduction mechanism. By applying high pressure or varying the Ce content of Y‐doped BaMO3, it is demonstrated that the proton conductivity follows the Meyer–Neldel rule (MNR) well. In the Arrhenius plot, the conductivities intersect at an isokinetic temperature, where the proton conductivity is independent of activation energy. Considering the relationship between isokinetic temperature and lattice vibration frequency, a high isokinetic temperature is observed in materials with stiff lattices, consisting of light atoms and small MO bond length. Based on consideration of the MNR, it is suggested that the enhancement of proton conductivity at low temperature can be well achieved by tuning lattice vibration frequency toward a desired isokinetic temperature.

Description of AC conductivity via Meyer-Neldel rule: A comparative study between oxide and chalcogenide systems

Nature of conductivity spectra in oxide and chalcogenide systems are found to be different, which should be indication of different conduction mechanisms via polaron hopping. This behaviour has been well explored using Meyer–Neldel rule (MNR), which provides microscopic information regarding conduction nature in different systems. Optical phonon assisted polaron hopping should impart this multiexcitation process of MNR. Microstructural information of present systems is also found to be helpful to validate conductivity data. A schematic model (nanocluster model) has been proposed to describe conduction mechanism in these complicated disordered solids. TEM micrographs and selected area electron diffraction (SAED) patterns reveal the agglomerates (cluster) in the oxide system, which may be favourable for stability of the system. More dislocations in the chalcogenide system should make the system unstable. This feature of instability should make them suitable candidates for more doping, which should increase their semiconducting nature.

Understanding transport properties of conducting solids: Meyer-Neldel rule revisited

Understanding transport properties of conducting solids: Meyer-Neldel rule revisited

Introducing effective temperature into Arrhenius equation with Meyer-Neldel rule for describing both Arrhenius and non-Arrhenius dependent drain current of amorphous InGaZnO TFTs

The drain current of the amorphous InGaZnO thin-film transistors (TFTs) shows the Arrhenius and the non-Arrhenius dependence at the high temperature and the low temperature respectively. The gate-voltage-dependent effective temperature is introduced into the Arrhenius equation. Considering the normal Meyer-Neldel (MN) rule and the inverse MN rule, the equation successfully describes both the Arrhenius and the non-Arrhenius dependent drain current at the low and the high gate voltage. The calculated results of the equation are verified by the available experimental data of the amorphous La-doped InZnO TFT and the amorphous InGaZnO (InO3:Ga2O3:ZnO = 1:1:1 mol%) TFT.