Negative Temperature Coefficient Of Resistance Research Articles

A Comprehensive Study of Cu/W Double Substitution in Strontium Manganate Ceramics for Some Device Applications

AbstractIn this communication, the synthesis and characterizations of modified strontium manganate (SrCu1/3Mn1/3W1/3O3) (SCMWO) by high‐temperature solid‐state method are reported. The structural analysis predicts a monoclinic structure with a crystallite size of 36.8 nm. The analysis of the Raman active modes reveals the presence of all the constituent atomic vibrations. The study of the ultraviolet–visible spectrum provides a bandgap energy of 1.71 eV, which may be suitable for photovoltaic applications. A Maxwell‐Wanger type of polarization effect is observed at low frequency while low dielectric loss makes the material suitable for energy storage devices. The study of the impedance plots reveals the negative temperature coefficient of resistance (NTCR) character. The activation energy increases with both frequency and temperature in the modified perovskite suggesting that conductivity of the sample increases and material characters are changing from dielectric to semiconducting. The symmetrical curves in the electrical modulus plots and shift toward higher frequency region agree with the results of the non‐Debye‐type of relaxation mechanism. The semicircular curves in the Cole–Cole plots confirm the semiconducting nature and are also well supported by the results of Nyquist plots. The studied material exhibits a semiconductor nature, which may be found suitable for energy storage device applications.

Deep Learning‐Assisted Sensitive 3C‐SiC Sensor for Long‐Term Monitoring of Physical Respiration

AbstractIn human life, respiration serves as a crucial physiological signal. Continuous real‐time respiration monitoring can provide valuable insights for the early detection and management of several respiratory diseases. High‐sensitivity, noninvasive, comfortable, and long‐term stable respiration devices are highly desirable. In spite of this, existing respiration sensors cannot provide continuous long‐term monitoring due to the erosion from moisture, fluctuations in body temperature, and many other environmental factors. This research developed a wearable thermal‐based respiration sensor made of cubic silicon carbide (3C‐SiC) using a microfabrication process. The results showed that as a result of the Joule heating effect in the robustness 3C‐SiC material, the sensor offered high sensitivity with the negative temperature coefficient of resistance of approximately 5,200ppmK‐1, an excellent response to respiration and long‐term stability monitoring. Furthermore, by incorporating a deep learning model, this fabricated sensor can develop advanced capabilities to distinguish between the four distinct breath patterns: slow, normal, fast, and deep breathing, and provide an impressive classification accuracy rate of ≈ 99.7%. The results of this research represent a significant step in developing wearable respiration sensors for personal healthcare systems.

Examining the effects of sintering temperature on double perovskite La2NiTiO6: Analysis of structural, optical, electrical properties, and leakage current characteristics

This study explores the influence of varying sintering temperatures on the structural, optical, electrical, and leakage current features of La2NiTiO6 (LNTO), a double perovskite material synthesized through the citrate auto-ignition method. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray (EDX) analysis were employed to investigate the structure, microstructure, and compositional distribution of the samples. The samples sintered at various temperatures showed the monoclinic structure with space group P21/n and were confirmed by Rietveld's refinement of the XRD patterns. The average grain size increased with higher sintering temperatures, which is consistent with the particle size estimated from the histogram plot of the FE-SEM data. The UV–visible (UV–Vis) spectroscopy showed that the energy band gap decreased as sintering temperatures increased. Impedance spectroscopy analysis revealed non-Debye type relaxation of charge carriers and confirmed the negative temperature coefficient of resistance (NTCR) behavior. Electrical analysis affirmed that the direct current (DC) conductivity is thermally activated, following the Arrhenius equation with an inverse temperature dependency. As the sintering temperature increases, the leakage current density decreases, and the leakage current conforms to the ohmic conduction mechanism.

Microstructural and dielectric characteristics of the Ce-doped Bi\(_{2}\)FeMnO\(_{6}\)

A double-perovskite material Bi2FeMn0.94Ce0.06O6 (BFMCO) was synthesized by solid state reaction technique and characterized it by various techniques (structural, microstructural, dielectric, impedance and modulus properties). The material has an orthorhombic crystal structure with an average crystallite size of 52.4 nm, as revealed by X-ray diffraction data (XRD). The scanning electron microscope (SEM) image shows the presence of nano rod-shaped grains and well-defined grain boundaries in this material, with an average grain size of 21.8 µm. The Energy dispersive X-ray (EDX) analysis and color mapping confirm the purity and the composition of the material. The dielectric, impedance and modulus properties are investigated in the temperature range of 25℃ to 500℃ and frequency range of 1 kHz to 1 MHz. The material exhibits a high dielectric constant at low frequency region and a low dielectric loss, which make it a suitable candidate for better energy storage devices. The impedance study reveals the negative temperature coefficient of resistance (NTCR) behavior of the material. The modulus study indicates the non-Debye relaxation of the material. The semi-conducting nature of the material is verified by the semi-circular arcs observed in both Nyquist and Cole-Cole plots. Thermally activated conduction mechanism is confirmed from ac conductivity study.  

Intense thermal shock generators made of micron-thick SnO2 layers for the on-chip rapid thermal processing in air

Thermal shock-resistant heaters are essential in various electronic devices, including chemical sensors and pyroelectric electron emitters. The advent of ultrafast high-temperature sintering and shock synthesis of nanomaterials has increased the demand for air-operating high-rate joule heaters. Moreover, incorporating such heaters at the chip level would revolutionize current rapid thermal processing methods in semiconductor technology. Here, transparent micron-thick SnO2 resistors are grown by spray pyrolysis on alumina, silica, and oxidized silicon chips and used as thermal shock-resistant air-operating heaters. These heaters can generate repeated heating cycles at rates of 15,000 °C/s up to 900 °C/s. Tin is a group IV element and its impact on Si- and SiO2-based devices is minimal making the presented device silicon compatible. The superior performance of the presented heaters is attributed to the tin oxide’s unique combination of physicochemical properties including high-temperature chemical stability in oxidizing atmospheres, suitable intrinsic conductivity, and optimal negative temperature coefficient of resistance. The application of the SnO2 heaters for the rapid on-chip high-temperature oxidation and sintering of low-melting-point metal thin films, while preserving the metal layer’s nanotexture, is demonstrated.

Ti3C2Tx MXene-based all-resistive dual-mode sensor with near-zero temperature coefficient of resistance for crosstalk-free pressure and temperature detections

All-resistive pressure and temperature dual-mode sensors are always a focus of attention in the field of flexible tactile sensing due to the lack of need for complex readout systems. However, the intrinsic temperature coefficient of resistance (TCR) of the active material greatly limits crosstalk-free detection of pressure. Herein, a near-zero TCR of −2.1 × 10−3% °C−1 has been achieved from a simple sandwich structure with a Ti3C2Tx MXene film printed on a polyethylene terephthalate substrate and encapsulated by a polydimethylsiloxane (PDMS) film. The mechanism is explained by the combination of PDMS thermal expansion and the negative TCR of MXene, which is certified by the simulations of their mechanical, thermal and electrical properties. In addition, a silver film is printed on the PDMS surface in contact with MXene film to form a temperature-independent pressure sensor based on two-phase contact mechanism with different conductivities. Moreover, a pressure-independent temperature sensor is constructed by opening a square hole in the PDMS encapsulated above another MXene film. Given their independent structures, the dual-mode sensing units are flexibly expandable on the same substrate to suit various application scenarios. For example, they are integrated into a glove to detect pressure and temperature without crosstalk in multiple states. Owing to the exceptional crosstalk-free detection and expandability, the sensor developed in this work hold immense promise for multifunctional tactile sensing.

Dielectric, electric, and magnetic response of modified bismuth ferrite-based double perovskites for NTC-thermistor application

Owing to the variation of the characteristics due to the cationic substitution of diverse elements at both A and B sites, the new polycrystalline double perovskite BaBiFeMnO6, synthesized via a cost-efficient solid-state reaction route. Initial structural refinement by Rietveld analysis reveals material crystallised in dual phases i.e. monoclinic and orthorhombic. The respective cell parameters for monoclinic as well as orthorhombic phases are a = 5.5881 Å, b = 5.6541 Å, c = 7.9186 Å with cell angles α = γ = 900 and β = 89.90810 and a = 5.4807Å, b = 5.3583Å, c = 7.4045Å and refined angles are α = β = γ = 900 respectively. The microstructural interpretation of the present sample reflects a non-uniform distribution of the grains with an average grain size of 2.97 μm with a mean crystalline size of 342.65 nm. The Fourier-Transform Infrared Spectroscopy (FTIR) graph indicated that the sample belongs to the perovskite family. The impedance measurement was carried out in a selected frequency and an assigned temperature range to investigate the electrical features of the material which suggested the non-Debye type relaxation and negative temperature coefficient of resistance (NTCR). Furthermore, the thermistor constant (β) and temperature coefficient of resistance (TCR) contributed to investigating the NTCR characteristic of the sample under NTC-type thermistor applications. The room temperature dielectric constant is 1707.67 with a minimal tangent loss of 0.7069 at 100Hz frequency has been estimated by fitting the dielectric data by utilizing the Havrilliak-Negami function. The polarization (P) induced due to the maximum applied electric field of 1.287 kV is studied from the hysteresis loop plotted between them. The hysteresis loop indicates the ferroelectric property of the material with a lossy nature. The room temperature remnant magnetization (2Mr) of 0.4424 emu/g and coercivity (2Hc) of 6.2 kOe have been estimated from the M ∼ H loop. The potentiality of the material to be used as a viable candidate in various energy storage devices and supercapacitors is suggested by all of the characterisations in conjunction with the high value of εr i.e. ∼80000 at 300 °C for the lower frequency.

Experimental determination of electrophoretic deposition parameters and electrical characterization for K 0.5 Na 0.5 NbO3 perovskite thick films for energy harvesting applications

Globally, depleting non-renewable energy resources and environmental pollution are significant challenges. Much research is ongoing on perovskite coatings as a potential replacement. In this work, potassium sodium niobate (KNN) ceramics are fabricated by solid-state method, calcined at ∼850 °C, and electrophoreticcally deposited (EPD) on Ni-substrate uniquely then, sintered at high temperatures ∼1070–1120 °C. The X-ray diffraction and FTIR confirmed the development of a pure KNN perovskite structure and metallic bond groups (-O-Nb-O) present respectively. An increase in the sintering temperature resulted in the pronounced peaks observed in KNN ceramics, confirmed by Raman spectroscopy, and easily observed in SEM having “square” and “circular” morphology with grain growth. The coating thickness was measured around 18–116 μm and increasing deposition rate (0.084–0.337 μm/s) was calculated. The coating roughness (∼813 nm) was confirmed by atomic force microscopy. Complex impedance spectroscopic (CIS) analysis confirmed the high dielectric constant (∼4789) with a high transformation and curie temperature (TO→T ∼ 280 °C & TC ∼ 480 °C), respectively. The increasing conductivity (≥830 μS/m) at higher frequency and temperatures agree with the hopping conduction mechanism which confirmed the negative temperature coefficient of resistance (NTCR). The work holds great significance in sensors, actuators, spintronics, and energy harvesting applications.

Electrical characterization of Sn modified barium bismuth zirconate

BaBi4Sn4O15, a Sn-modified ceramic sample of layered ferroelectric oxide family, is developed using a high-temperature mixed oxide route after firing for calcination at 810 °C for 6 h in steps of 50 °C starting from 600 °C. An introductory XRD study of the compound displays the development of the new orthorhombic structured single-phase compound at atmospheric conditions. The electrical behaviors of the compound are investigated in a wide temperature span (30–500 °C) and frequencies ranging from 0.1 kHz to 1 MHz using an impedance analyzer. Dielectric behavior informs that the compound has a phase transition from Ferro to Paraelectric at 370 °C, which is well above room temperature. The impact of temperature and frequency on complex immittance parameters (impedance and modulus) is analyzed using an LCR meter in a broad temperature & frequency span. The electrical properties confirm; (a) the existence of semiconductor-like NTCR (negative temperature coefficients of resistance) behavior, (b) the evidence of the electric relaxation process as a function of temperature, (c) the existence of electric relaxation ascribed to the simultaneous contribution of bulk & bulk interfaces to the electrical behavior, and (d) presence of the non-Debye type relaxation phenomena. The frequency-dependent conductivity follows Jonscher’s universal power law.

Microstructure, dielectric, and impedance spectroscopy of the dysprosium-modified LaBiO3 ceramic

We report the structure, microstructure, dielectric, and transport properties of the dysprosium (Dy) modified lanthanum bismuth oxide (LaBi0.85Dy0.15O3) synthesized by the solid-state reaction method. The Rietveld refinement of the X-ray diffraction (XRD) data was done using MAUD software which adopts an orthorhombic crystal system. Scherer’s formula was used to calculate crystallite size, which is found to be 25.2 nm. An analysis of a scanning electron microscope (SEM) image indicates that the grains have an even distribution throughout the whole sample surface with well-defined grain boundaries. Once more, compacted grains and clearly defined grain boundaries may have an impact on the conduction mechanism in the sample. The energy dispersive analysis of the X-ray (EDX) spectrum provides that all the constituent elements are present in the both weight and atomic percentage in the sample. The generated sample appears to reflect the Maxwell–Wagner type of dielectric dispersion, in accordance with research on the dielectric characteristics as a function of temperature and frequency. While impedance evaluation confirms the existence of the negative temperature coefficient of resistance (NTCR), the modulus plot analysis indicates a non-Debye kind of relaxation mechanism. A thermally activated conduction mechanism is present, according to the study of the ac conductivity plot. Again, the study of the Nyquist and Cole–Cole plots shows that semiconducting behavior is consistent with several applications involving energy storage devices.

Non-bridge NTC thermistor anemometer with programmable sensitivity

This paper presents a programmable constant temperature anemometer (CTA) with a voltage control of the negative temperature coefficient (NTC) thermistor's working temperature. The CTA uses a non-bridge regulating circuit, outputting voltage, current and power dissipation signals. Its operation and sensitivity control are tested for NTC temperatures in a 45 to 85°C range, at wind speeds up to 14m/s. The power sensitivity at 25m/s is improved by NTC temperature increase, estimated to be 6.74mW/(m∙s−1) at 85°C. A qualitative analysis of circuit's stability is derived, providing the guidelines for bandwidth optimization. The NTC's resistance is regulated with error of 0.9% for working temperatures over 60°C. The demonstrated programmability of NTC temperature allows for implementation of known temperature compensation and measurement techniques utilizing a single sensor, while permitting continuous sensitivity control. This makes it suitable for measurements with varying ambient conditions.

Effect of Frequency and Temperature on Dielectric and Transport Properties of CaO stabilized ZrO2@mullite composites

AbstractThis study concerns the synthesis and structure related electrical property analysis of CaO doped ZrO2@mullite composites. Two synthesis techniques (solid state reaction route and thermal plasma sintering) are used which results the formation of a composite consisting of mixed phase of orthorhombic mullite, tetragonal and monoclinic zirconia. The lattice parameters, residual strains, average crystallite size and cell volume of these CaO‐doped ZrO2@mullite composites are obtained from XRD analysis. Stabilization of t‐ZrO2 phase at room temperature is confirmed. Porous microstructure observed in SEM images results in low dielectric constant value of these composites. At room temperature and selected frequency of 1MHz, the dielectric constant and loss factor of 4.7 and 3.826 × 10−2 is observed for conventional CaO stabilized ZrO2@mullite composite and that of 3.8 and 2.19 × 10−2 is reported for plasma sintered CaO stabilized ZrO2@mullite composite. The impedance spectroscopic analysis demonstrates the negative temperature coefficient of resistance (NTCR) behavior and non‐Debye type relaxation behavior of both the CaO stabilized ZrO2@mullite composites. A negligible effect of electrode polarization is realized in these composites. The electronic band gap of conventional and plasma sintered CaO stabilized ZrO2@mullite composites is found to be around 3eV.

High specific capacitance and NTC behavior of substituted cobalt oxide spinels for electrochemical supercapacitor and thermistor applications

Due to the growing importance of low-cost energy storage devices in smart device applications, finding an appropriate electrode material with the least self-discharging, high power, and energy densities is the need of the hour. In this paper, Cu and Mn-modified Co3O4 spinels in the form of CuCo2O4 and MnCo2O4 are reported as the most promising electrode materials for high-performance electrochemical supercapacitors. Modified Co3O4 spinels were prepared by the co-precipitation technique, and the X-ray diffraction (XRD) studies show a single-phase formation with cubic crystal symmetry. The average crystallite size estimated by considering the highest intensity peak of the diffraction pattern using Scherrer’s relation shows the average crystallite size below 30 nm for reported spinels. Scanning electron microscopic (SEM) images stabilize the fact that grains with nanosizes consisting of regular shapes and excellent morphological features. The dc-conductivity measurement establishes the essence of negative temperature coefficient of resistance (NTCR) behavior in nanostructured spinels. The specific capacitance (Cs) of CuCo2O4 and MnCo2O4 estimated using cyclic voltammetry (CV) was found to be 616.074 F g−1 and 1401.16 F g−1 for a scan rate of 10 mV s−1 with verified stability up to 1000 cycles. The low internal resistance value in the range of 0.1 Ω for both the spinels verified by the electrochemical impedance spectroscopy (EIS) graph confirms these spinels as encouraging electrode materials for electrochemical supercapacitors.

Study of Structural, Dielectric, and Electrical Properties of Gadolinium-Modified Bismuth Lanthanum Oxide

In this article, synthesis (solid-state reaction) and characterization (structure, microstructure, and electrical) of the gadolinium (Gd) modified bismuth lanthanum oxide (LaBi0.9Gd0.1O3, and LBGO) are reported. Rietveld refinement of the x-ray diffraction (XRD) data was done using MAUD software, which adopts an orthorhombic crystal symmetry. The average crystallite size in the prepared sample was calculated using Scherer’s relation. Scanning electron microscope (SEM) micrograph analysis reveals that grains are uniformly distributed over the sample’s surface through well-defined grain boundaries so that a dense sample is formed, which may be a possible reason for elevated dielectric properties. The study of energy dispersive analysis of the x-ray (EDX) spectrum confirms the presence of all constituent elements (Bi, La, Gd, and O) in the studied sample. The presence of Maxwell–Wagner type of dispersion is confirmed from the study of dielectric properties as a function of frequency. The analysis of the modulus study confirms the presence of a non-Debye type of relaxation. The negative temperature coefficient of resistance (NTCR) nature of the sample is confirmed by the impedance study. The study of ac conductivity suggests the presence of a thermally activated relaxation process in the studied sample. Again, analysis of the Nyquist plots confirms the semiconducting character and may be suitable for some energy storage devices applications.

Electrical transport properties of Mn-modified Ba0.5Bi0.5Ti0.5Fe0.5O3

Ba0.5Bi0.5Ti0.5Fe0.5Mn0.1O3, a Fe-based Mn-modified BFO-BT ceramic, is processed by solid-state reaction route, calcined at 950 °C temperature. Formation of single-phase orthorhombic structure is observed from room temperature XRD analysis. Dielectric behavior is investigated over a broad range of temperature (30 °C–500 °C) and frequency (0.1 kHz–10 MHz). Broadening of transition temperature is noticed at 460 °C, where the material undergoes a change from ferro- to paraelectric state. From dielectric plots the effect of Mn on capacitive behavior of the material is studied. The conductivity study exhibits negative temperature coefficient of resistance (NTCR) behavior showing semiconducting behavior of the material.

Structure, dielectric, vibrational, and optical properties of lead-free double perovskite Bi2FeMnO6

The solid-state reaction technique was executed to form a hexagonal double perovskite Bi2FeMnO6 nanopowder. X-ray diffraction (XRD) analysis gives information regarding the product’s average crystallite size of 27.9 nm and lattice strain of 0.00125, respectively. The Ultra-Violet (UV) visible spectroscopy data provides a band gap energy of 2.49 eV, which may be a suitable range for photovoltaic applications. Fourier Transform Infrared (FTIR) spectroscopy data analysis reveals the presence of all constituent atomic vibration bands. The dielectric measurements confirmed the presence of the Maxwell-Wanger type of dispersion. The negative temperature coefficient of resistance (NTCR) character is well understood from impedance spectroscopy. The electrical modulus results indicate the presence of a non-Debye-type of relaxation mechanism in the sample. Analyzing ac conductivity data reveals the thermally activated conduction process. The sample’s semi-conducting character was confirmed by both Nyquist and Cole-Cole plots.

Metal chalcogenide nanorings for temperature-strain dual-mode sensing.

Most metal chalcogenides exhibit layered structures and anisotropic morphologies such as nanosheets, nanoplates, and nanotubes, as well as nanosheet-assembled nanoflowers. Unconventional morphologies such as nanorings may bring appealing properties to functional materials, but they have not been realized with metal chalcogenides. Herein, we report that Sn0.2Mo0.8S2 nanorings with a mixed 1T/2H phase were synthesized by etching SnS2 cores from Sn1-xMoxS2/SnS2 lateral heterostructures. Flexible electronic sensors based on these Sn0.2Mo0.8S2 nanorings exhibited excellent temperature and strain sensing performance, with a negative temperature coefficient of resistance of -0.013 °C-1 and a minimum detectable strain of 0.09%. In addition, the dual-functional flexible electronic sensors with easy fabrication and good wearability showed great promise for tracking human activities and monitoring inapparent health-related signals.

Understanding the impact of Ca doping on structural, morphological and low temperature transport properties of Nd2NiMnO6

Double perovskites of the form R2NiMnO6 (R=Rare-earth) are recognized for their multifunctional nature. Here in this study we have considered one of the members of this class of double perovskites i.e., Nd2NiMnO6 and modified its various physical properties through Ca doping at Nd site. X-ray diffraction patterns and their analysis show the monoclinic structure that can be indexed with P21/n space group for all the three compounds of Nd2-xCaxNiMnO6 (x = 0.0, 0.2 and 0.4). Scanning electron microscopy shows that the grains are irregular in shape and size for the three samples and the average grain size decreases with increase in Ca concentration. The variation of dielectric constant as well as dielectric loss with frequency depicts a decrease in their value with increase in frequency from 20 Hz to 2 MHz. On the other hand the variation of dielectric constant with temperature shows a rise in the value of dielectric constant as the temperature is increased from 100 K to 300 K, while the temperature variation of dielectric loss is associated with relaxation behavior. The peak in the tanδ curve corresponds to the temperature at which the dielectric constant starts increasing and this peak in the dielectric loss gets shifted towards the side of high temperature with the rise in frequency. A rise in the Ca concentration increases the dielectric constant as well as dielectric loss. The ac conductivity for all the three samples of Nd2-xCaxNiMnO6 (x = 0.0, 0.2 and 0.4) rises with rise in temperature indicating the existence of negative temperature coefficient of resistance. The ac conductivity also increases with increase in Ca concentration. A further analysis of conductivity behavior has been done by determining the activation energy through the involvement of the Arrhenius equation. The activation energy decreases with increase in Ca concentration. The resistivity measurements again indicate the existence of negative temperature coefficient of resistance in all the three samples of Nd2-xCaxNiMnO6 (x = 0.0, 0.2 and 0.4) and the value of resistivity reduces as the Ca concentration is increased. The various results obtained in this study have been interrelated.

Exploring the comparison of optical, dielectric and photocatalytic performance of Yb3+ and Gd3+ half-doped DyCrO3 nanostructures

The auto combustion sol-gel method was utilized to prepare Dy0.5Gd0.5CrO3 (DGCO) and Dy0.5Yb0.5CrO3 (DYCO) nanomaterials. The single-phase formation of materials was confirmed with the X-ray diffraction technique. Utilizing Kubelka-Munk function, the optical bandgap energy values were found to be 3.39 eV (DGCO) and 2.61 eV (DYCO). The dielectric properties were analyzed in frequency range from 10 kHz to 2 MHz and a temperature range from 25 °C to 225 °C. The conduction mechanism followed the universal Jonscher's power law, which revealed that conduction process was primarily governed by the small polaron hopping. The CBH, NSPT, and QMT models were applicable for the a.c. conduction in the DGCO nanomaterial whereas the CBH and NSPT models were more appropriate for the DYCO nanomaterial. The Kohlrausch, Williams and Watts function was used to correlate the imaginary electrical modulus spectrum, which confirmed that the relaxation process in the materials was non Debye-type. An impedance spectroscopic measurement revealed the influence of grain and grain boundaries and it followed negative temperature coefficient resistance behaviour at higher temperatures. Both DGCO and DYCO nanomaterials were also investigated for their photocatalytic degradation of Rhodamine B (RhB) and Methylene Blue (MB) dyes. The degradation, under direct solar irradiation, was 84 % (RhB) and 63 % (MB) for DYCO nanomaterial and 54 % (RhB) and 44 % (MB) for DGCO nanomaterial, indicating their potential in water treatment.

Electron Theory of Metals - Answers to Unsolved Problems/Questions

Why are there simple metals with positive thermopower? Why are there metals with a negative temperature coefficient of resistivity? What is the reason for the Mooij correlation and the Giant Hall effect?
 These are questions that have not yet been answered with the known transport theories (Mizutani, 2001, pp. 474). However, they can be answered by considering the phenomenon of phase separation connected with an electron transfer between the phases. In this paper answers are proposed to these questions mentioned. Answers to other fundamental problems/questions are proposed in the recently published book (Sonntag, 2023).