Negative Temperature Coefficient Thermistors Research Articles

Effects of Ni cation ratio and sintering temperature on microstructure and electrical properties of NiMnCoO4-based ceramics

Negative temperature coefficient (NTC) thermistors as temperature sensors play an important role in various electrical/electronic devices and are widely applied in the fields such as, automotive sensor modules, home appliances and control applications. The electrical properties of NTC thermistors can be effectively controlled by regulating the content of their chemical components or changing the microstructures. Therefore, this study investigated the effects of Ni cation ratio and sintering temperature on microstructures, crystal structures, and electrical properties of NiMnCoO4-based ceramics. With increasing Ni content, it was found that sinterability of NiMnCoO4-based ceramics was decreased with forming rock-salt phase of NiO, resulting in degrading resistivity. Furthermore, the spinel structures were detected by X-ray diffraction analysis regardless of sintering temperatures. Notably, values of average grain size for sintered samples were increased with increasing sintering temperature. Besides, it was clarified that electrical properties were significantly influenced by average grain size. The room temperature resistivity was increased from approximately 300 kΩ⋅cm for the sintered sample at 1100°C to about 600 kΩ⋅cm for for the sintered sample at 1300oC. On the other hand, the B(25/85) constant was not significantly influenced by the sintering temperature. Accordingly, it is expected that the results of this study are useful for controlling electrical properties of MnCoNiO4-based ceramics.

Accelerating the screening of high-entropy Co-Mn-Fe-Ni-Zn-O gradient films for highly stable NTC materials through co-sputtering combinatorial synthesis

High-entropy negative temperature coefficient (NTC) thermistor thin films, renowned for their exceptional stability, represent a significant advancement in the field of temperature measurement, facilitating the miniaturization of next-generation information and electronic devices. However, “trial and error” approach to developing multi-component NTC oxides significantly constrains the efficiency of the design process. To accelerate development process, we prepared Co-Mn-Fe-Ni-Zn-O gradient films by co-sputtering combinatorial synthesis. The effects of stoichiometric ratios on the resistance (R25), material constant (B25/50) and stability (ΔR/R0) of gradient films were visually represented through color-coded maps for straightforward and intuitive analysis. Samples close to the MnCoFe target in gradient films showed a trend of decreasing resistance and increasing material constant, both reaching 1.71 MΩ and 4083 K, respectively. The high-entropy Co21Mn17Fe19Ni21Zn22O4±δ film exhibited the lowest resistance drift rate only 2.68 % after 500 h ageing at 125 ℃. Another delightful result was that the corresponding homogeneous films, achieved through sputtering with a composite target, had a relative deviation in resistance drift rate of merely 0.18 %. This showcased the successful translation from the screening outcome to the homogeneous film, significantly accelerating the development of NTC materials via the utilization of gradient films screening.

Enhanced thermal constant B of diamond films for ultrahigh sensitivity negative temperature coefficient thermistors

Enhanced thermal constant B of diamond films for ultrahigh sensitivity negative temperature coefficient thermistors

Development of Lead‐Free Defect Brownmillerite Perovskite Ceramic LiBiFeMnO5 Solid Solution for Electronic Devices

This article reports the fabrication (synthesis) and characterizations (structural, microstructural topographic surface, dielectric, transport, impedance, current–voltage, and resistive properties) of a complex lead‐free defect perovskite material of composition LiBiFeMnO5. A preliminary structural investigation of the X‐ray diffraction pattern using N‐TREOR09 methods shows monoclinic symmetry. The scanning electron microscopic spectrum examines the sample's microstructural topographic surface, fractal study, and roughness (using the standard ISO25178). The analysis of Maxwell–Wagner dielectric dispersion, relaxation, and transport mechanisms is investigated utilizing dielectric, impedance, and conductivity spectrum accumulated within the experimental frequency of (1 kHz–1 MHz) at different temperatures (30–500 °C). A nonoverlapping small polaron tunneling conduction mechanism and correlated barrier hopping mechanism in the material have helped to understand its conduction phenomena. The Ohmic and space–charge limited conduction mechanisms are investigated by the slope of the logarithmic electric field (E) and current density (J). The thermistor constant (β) is determined to be 1982.87. The temperature coefficient of resistance is found to be −0.00419, which may be suitable for negative temperature coefficient thermistors, sensors, and other related devices.

Doublet doped titanate ferroelectric system for capacitors and NTC thermistor applications

A simple negative temperature coefficient (NTC) thermistor Ba0.85Sr0.15Ti0.85Zr0.15O3 system is elaborated using a conventional solid-state reaction route. The structural analysis confirms that the elaborated pseudo-cubic system, which is indexed in the P4mm space group, exhibits one single phase. The dielectric properties and the electrical resistivity data are investigated over a large temperature range from 413 K to 673 K. In this temperature interval, the Steinhart–Hart equations are employed to confirm that Ba0.85Sr0.15Ti0.85Zr0.15O3 is a promising system for sensor application. Accordingly, the thermistor constant (β=10154 K), the sensitivity factor (-5.5 %/K≤α≤-2 %/K), the activation energy (Ea=0.875 eV), and the stability factor (SF=2.27) parameters are calculated to approve that Ba0.85Sr0.15Ti0.85Zr0.15O3 exhibits an NTC-thermistor behavior. The temperature dependence of the electrical resistivity confirms that Ba0.85Sr0.15Ti0.85Zr0.15O3 reveals a semiconductor behavior. The dielectric investigation shows that Ba0.85Sr0.15Ti0.85Zr0.15O3 exhibits a motivating dielectric properties (elevated dielectric constant value (105<ε’<106) and low dielectric losses (mostly < 0.007) with almost frequency independence between 20 Hz to 500 kHz). The colossal dielectric response of Ba0.85Sr0.15Ti0.85Zr0.15O3 is attributed to the internal barrier layer capacitor (IBLC) and the surface barrier layer capacitor (SBLC) effects. Such response suggests the suitability of Ba0.85Sr0.15Ti0.85Zr0.15O3 ceramic for high temperature capacitor applications.

Fabrication of novel (1-x)YMnO3-xCaCeNbWO8 composite ceramics with highly linear behavior for wide temperature range NTC thermistors

A novel YMnO3−CaCeNbWO8 negative-temperature-coefficient (NTC) composite ceramic system with highly linear behavior was fabricated by conventional sintering at 1400 °C for 8 h in air. A linear behavior between the natural logarithm of the resistivity (lnρ) and the reciprocal of the absolute temperature (1000/T) is the key to the application of high-temperature NTC thermistors. X-ray diffraction results indicated that the YMnO3−CaCeNbWO8 ceramics were mainly composed of tetragonal CaWO4 and cubic CaYNb2O7 phases. The investigation of the electrical properties revealed that within the temperature range of 25−1050 °C, the linearity between lnρ and 1000/T in the composite ceramic with x=0.7 reached 99.99 %. This result mainly depended on the evolution of the phase structure. Furthermore, the 0.3YMnO3−0.7CaCeNbWO8 composite ceramic exhibited high thermal stability with an aging coefficient of only 0.5 % after aging at 700 °C for 1000 h. Based on these characteristics, it is a potential candidate for high-temperature NTC thermistors.

Facile Synthesis of Novel Short-Chain Ligand-Capped Colloidal Metal Oxide Nanoparticles for Printed Flexible Devices.

Colloidal metal oxide nanoparticles are key materials for achieving cost-effective and large-scale production of flexible devices, as they enable the formation of functional oxide thin films at low temperatures (<400 °C) through printing techniques such as inkjet printing, gravure coating, and microcontact printing. The conventional solvothermal synthesis of colloidal metal oxide nanoparticles through the thermal decomposition of precursors results in particles with bulky, long-chain ligands on their surfaces, which hinder the formation of dense oxide films when depositing the colloidal metal oxide nanoparticles. Herein, we have developed a simple and versatile method for synthesizing colloidal metal oxide nanoparticles using base-induced hydrolysis and the condensation of metal acetates as precursors. Various binary and ternary colloidal metal oxide nanoparticles (CuO, Mn3O4, Co3O4, CeO2, In2O3, Co1.8Mn1.2O4) were synthesized using short-chain acetate ligands on their surfaces. The thin acetate ligand-containing colloidal Co1.8Mn1.2O4 nanoparticle film exhibited lower resistivity than the same with long-chain oleate ligands. The films coated onto a polyimide substrate formed a flexible negative temperature coefficient thermistor that exhibited the temperature dependence of resistance comparable to bulk materials with a bending durability of up to 5 mm radius. These findings highlight the effectiveness of utilizing colloidal metal oxide nanoparticles with short-chain ligands in flexible devices.

3D printing of thick film NTC thermistor from preceramic polymer composites for ultra-high temperature measurement

Integrating thick/thin film sensors into component systems has emerged as a prevalent approach for monitoring in extreme environments. However, traditional vapor deposition methods face obstacles, including complex fabrication processes and the degradation of sensitive materials at extremely high temperatures. This work delineates the development of a polysilazane composite dual-layer thick-film Negative Temperature Coefficient (NTC) thermistor characterized by its suitability for extreme temperatures and robust bond strength achieved through an advanced near-net-shape printing methodology. High-temperature resistant La(Ca)CrO3/polysilazane films were printed as the sensitive layer, while a dense layer formed by Cr2O3/polysilazane was used as the protective layer. The bilayer structure resulted in a 2.5-fold increase in adhesion strength compared to the single-layer La(Ca)CrO3/polysilazane films. Experimental results indicate that the dual-layer thick-film NTC thermistor can be operated long-term at 1300 °C with a resistance drift rate of 0.9 %/h and survive short-term exposure to temperatures up to 1550 °C. As a proof of concept, this work applied 3D printing technology to fabricate a polysilazane composite dual-layer thick-film NTC thermistor on the surface of turbine blades and demonstrated its functionality under flame impingement at nearly 1300 °C. Such flexible 3D printing techniques pave the way for a new paradigm in manufacturing sensors capable of withstanding ultra-high temperatures.

Investigation of structure, dielectric, thermistor, and optical properties study of an eco-friendly double perovskite for photovoltaic and optoelectronic applications: CaLiFeWO6

Double-perovskite oxides have received interest recently because of their appealing photovoltaic and optoelectronic properties for promising applications. In this paper, we demonstrate the synthesis (solid-state reaction) as well as characterization study of an eco-friendly novel double perovskite CaLiFeWO6. Preliminary investigation of X-ray diffraction (XRD) data reveals a monoclinic structure. Micro-lattice strain and average size of crystallite are found to be 0.000564 and 86 nm. The distribution of grains and elemental composition of the sintered sample was recorded using scanning electron microscope (SEM) cum energy dispersive X-ray spectroscopy (EDX). Raman scattering spectroscopy is tailored to study the vibrational Raman modes involved in the sample. The optical analysis was investigated by employing UV visible spectroscopy and used to obtain bandgap energy within the range for optoelectronic device applications. To understand the electrical behavior of the synthesized double perovskite, the authors conducted both low and high-frequency dielectric measurements and utilized impedance spectroscopy. The conductivity behavior in the studied material follows Jonscher's power law. Resistance versus temperature data supports the concept of negative temperature coefficient (NTC) thermistors for temperature sensors and temperature control systems. Polarization-electric field supports the possibility of ferroelectric behavior, which opens the door to a wide range of technological advancements and innovations in various fields.

Influence of cationic vacancy diffusion on the aging behavior of low-temperature SrCo1-xRuxO3 thermosensitive ceramics

The thermosensitive ceramics of negative temperature coefficient (NTC), SrCo1-xRuxO3 (0 ≤ x ≤ 0.8), were synthesized using the solid-phase method. The research systematically explored the phase structure, microstructure, elemental chemical states, electrical properties, and aging performance. X-ray diffraction (XRD) data indicates that with the increase of Ru content, the lattice parameter increases. Scanning electron microscopy (SEM) images reveal a dense and uniform microstructure. X-ray photoelectron spectroscopy (XPS) data indicates the presence of Co2+/Co3+ and Ru4+/Ru5+ ion pairs. Resistive temperature data indicates its potential use as a low-temperature thermosensitive resistance material in the range of 2–300 K. Fitting the resistance-temperature curve using the thermally activated band conduction model and Mott's 3D variable range hopping model. Proposed the Ru–O2--Co hopping model, elucidating the hole hopping transport mechanism in NTC ceramics. Impedance spectroscopy analysis indicates that grain boundary resistance dominates the overall resistance of the sample. After aging at 77 K for 864 h, the maximum aging drift rate of the ceramic material is 1.55 %. Proposed a novel cationic vacancy diffusion model to explain aging phenomena, offering a new perspective for designing high-stability low-temperature NTC thermistors.

Design of a Negative Temperature Coefficient Temperature Measurement System Based on a Resistance Ratio Model.

In this paper, a temperature measurement system with NTC (Negative Temperature Coefficient) thermistors was designed. An MCU (Micro Control Unit) primarily operates by converting the voltage value collected by an ADC (Analog-to-Digital Converter) into the resistance value. The temperature value is then calculated, and a DAC (Digital-to-Analog Converter) outputs a current of 4 to 20 mA that is linearly related to the temperature value. The nonlinear characteristics of NTC thermistors pose a challenging problem. The nonlinear characteristics of NTC thermistors were to a great extent solved by using a resistance ratio model. The high precision of the NTC thermistor is obtained by fitting it with the Hoge equation. The results of actual measurements suggest that each module works properly, and the temperature measurement accuracy of 0.067 °C in the range from -40 °C to 120 °C has been achieved. The uncertainty of the output current is analyzed and calculated with the uncertainty of 0.0014 mA. This type of system has broad potential applications in industry fields such as the petrochemical industry.

SiO2 and Fe cation synergistically modify the LaMnO3 NTC thermistors with high stability

SiO2 insulator and Fe2O3 dopant was simultaneously used to modify the crystalline phase, morphology and electric properties of LaMnO3 ceramics. Results show that there are several merits after modification. On the one hand, the addition of SiO2 is demonstrated to have multifunction to the LaMn1-xFexO3 (0 ≤ x ≤ 0.5) (LMFO) ceramics. After adding SiO2, the surface of LMFO ceramics tend to be flat, the degree of densification increases, the porosity decreases, and the pores almost disappear. Meanwhile, the resistance drift rate of LaMnO3 with SiO2 is reduced and the aging stability is improved. In addition, the crystalline structure of LMFO ceramics transform from hexagonal perovskite phase (x ≤ 0.2) to cubic perovskite phase (x ≥ 0.25) along with the Fe-doping contents increase. Moreover, the grain size decreases and the grain boundaries increase with the increase of Fe content. X-ray photoelectron spectroscopy (XPS) spectra show that both the Mn4+/Mn3+ ratio and the oxygen vacancy concentration decrease with increasing Fe content. Resistivity ρ25°C raised from 2.84 Ω cm to 65.38 Ω cm, and material constant B25/50 increased from 139.36 K to 1751.78 K. Fe doping significantly improves the stability of LMFO ceramics, and the minimum value of resistance drift rate is 0.168 % after aging at 125 °C for 500 h. The above results confirm that the SiO2 modified LMFO ceramic is a high stability negative temperature coefficient (NTC) thermistor.

Recovery of Ni-Co-Mn Oxides from End-of-Life Lithium-Ion Batteries for the Application of a Negative Temperature Coefficient Sensor

This study demonstrates the current advancements in battery management systems (BMSs), emphasizing the need for precise temperature monitoring within battery packs to enhance safety and performance through efficient thermal management. The increased demand for lithium-ion batteries (LIBs) has driven the development of temperature sensors with improved accuracy and stability. In particular, Ni-Co-Mn-based spinel oxides are commonly used due to their stable negative temperature coefficient (NTC) behavior. However, challenges arise in manufacturing due to the high cost and uncertain supply of critical cathode components (e.g., Co, Ni, and Mn) for LIBs. This research focuses on developing spinel-type (Ni0.6Co0.4Mn2)O4 using recycled Ni-Co-Mn oxides obtained from end-of-life (EOL) LIBs, demonstrating temperature resistance behavior suitable for temperature sensing. The oxides are prepared through hydrometallurgy, oxalate synthesis, and post-heat treatment. Successful integration into spinel-type NTC thermistors suggests broader applications in various industrial fields. A systematic investigation into the synthesis and characterization of recovered Ni-Co-Mn oxides from EOL LIB cathode materials (Li(Ni0.33Co0.33Mn0.33)O2) is presented for NTC thermistor application. Thermogravimetric analysis-derivative thermogravimetry (TGA-DTG) identifies the optimal post-heat treatment temperature. The X-ray diffraction (XRD) patterns confirm a cubic spinel structure of the Ni-Co-Mn oxides, supported by scanning electron microscope (SEM) images showing a uniform microstructure. Also, energy dispersive X-ray spectroscopy (EDS) mapping confirms homogeneous element distribution. Recovered oxide pellets from the sintering process exhibit a single spinel structure, with X-ray photoelectron spectroscopy (XPS) analysis revealing changes in the valence states for Ni and Mn. Resistivity measurements demonstrate semiconductive behavior, which shows a B value (3376.92 K) suitable for NTC thermistor applications. This study contributes valuable insights to black powder recycling from EOL LIBs and its potential in temperature-sensitive electronic devices.

Can ZrAlN thin films be used as thermistor sensors for temperature assessment?

The electrical characteristics and conduction mechanisms of ZrAlN thin films for their potential use as thermistor sensors were assessed. Various compositions of Zr1-xAlxN were synthesized by sputtering and studied up to 200 °C to understand their sensitivity and applicability. Among the compositions studied, the ones with x = 0.34 and x = 0.46 showed the highest sensitivities, reaching values close to 3000 K. However, the thermo-resistive properties exhibited by these compositions limited their utilization above 100 °C. Zr1-xAlxN film compositions with x higher than 0.46 showed amorphous structures and were found to be insulative. Composition with x = 0.26, within the cubic phase, showed the most promising electrical properties regarding temperature sensing in the studied range. XPS analysis of this composition confirmed the presence of Zr-N and Al-N bonds, with a Zr3+ oxidation state, which suggests the availability of a free electron contributing to the electrical conduction. Impedance measurements performed at different temperatures for this composition revealed the dominant role of the grain boundaries in the conduction mechanism, based upon electron hopping between grains, overcoming the energy barrier imposed by the grain boundaries. ZrAlN thin films demonstrate negative temperature coefficient (NTC) thermistor behavior, expanding their applications beyond protective coatings to temperature monitoring.

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.

A novel linear temperature thermistor in the xAl2O3-(1-x)CdSnO3 system

Negative Temperature Coefficient (NTC) thermistors, known for their high sensitivity and fast response, find wide applications in national economy, military, aerospace and various other fields. The study of NTC thermistors with linear temperature-resistance is of great significance in streamlining circuit designs and developing high-performance electronic ceramics. This study focuses on the synthesis of a linear thermistor material in xAl2O3-(1-x)CdSnO3 system by a solid-phase reaction method. Through the introduction of th high-resistance Al2O3 phase, a three-dimensional conductive network is established with Al2O3 and CdSnO3, resulting in the acquisition of linear electrical properties. These properties have exhibited excellent linear NTC variation within the temperature range of 308 K–458 K. Notably, at x = 0.2, the thermistor shows the highest linearity (R2 = 0.9984). Additionally, the complex impedance spectral analysis has helped build resistive and capacitive conductivity models revealing the linearization mechanisms.

Synthesis of a scheelite barium molybdate: Structural, topological, electrical, and transport properties for negative temperature coefficient thermistor application

Preliminary structural analysis of Scheelite barium molybdate BaMoO4 (BMO) ceramic using NTREOR-09 and McMaille methods has confirmed the tetragonal symmetry with room temperature X-ray diffraction (XRD) spectrum. Further, other structural parameters like crystallite size and compressive lattice strain are found to be of 31 nm and −0.00151 respectively. The topographical study of scanning electron microscope (SEM) image confirms the polycrystalline nature with no other impurities in the sample. Detailed analysis of dielectric permittivity (εr), and loss (tanδ) supports Maxwell-Wagner and Koop's phenomena. The non-overlapping small polaron tunnelling (NSPT) and correlated barrier hopping (CBH) model have emphasis on transport mechanism. The presence of semiconducting behavior of the scheelite material at various temperatures and frequencies examined by complex impedance and modulus spectra. The value of grain resistance decreases as temperature increases demonstrating the existence of negative temperature coefficient (NTCR) behavior of the material. The increase of the value of thermistor constant (β) (67.339, 516.613, and 772.485 in the different high-temperature range) suggests an efficient application of the material for NTC-thermistor.

Sintering and electrical properties of Mn–Co–Fe–Zn–Ni–O high-entropy ceramics for NTC thermistors

In this work, the dual-phase structure Mn–Co–Fe–Zn–Ni–O high-entropy negative temperature coefficient (NTC) ceramics were synthesized by a solid-phase reaction method. The ceramics are mainly composed of the cubic spinel phase and the rock salt phase. Electron microscopic images revealed the typical morphology and the homogeneous distribution of all elements. The results confirmed that the microstructure and electrical properties of the high-entropy ceramics are closely related to the sintering temperature. As the sintering temperature increased, the content of the rock salt phase gradually improved, meanwhile, the higher resistivity of samples was achieved. Notably, it was found that an appropriate proportion of the rock salt phase could significantly enhance the aging stability of ceramics. The aging drift of the samples sintered at 1175 °C was only 0.632 %. In addition, the ratio of the two phases was adjusted by adding NiO. The ρ25 and B25/50 of the materials can be tuned in the range of 22.25 kΩ cm∼24.19 kΩ cm and 4047 K–4145 K, respectively. Regulating the phase ratio of dual-phase materials is a novel strategy for designing NTC ceramic materials with excellent characteristics. This work provides an idea for future research on high-entropy NTC thermistor ceramics.

High-entropy (Co0.2Mn0.2Fe0.2Zn0.2Al0.2)3O4 thick-film NTC thermistor with high aging stability and wide temperature measurement range

Here, a novel type of high-entropy (Co0.2Mn0.2Fe0.2Zn0.2Al0.2)3O4 solid-solution ceramics with spinel phase structure was designed and successfully fabricated based on an entropy engineering approach. Additionally, the impact of sintering temperature, a critical factor in entropy stabilization, on structural and electrical behavior was systematically examined at a range of 1110∼1150 °C. The results indicate that each synthesized sample exhibits a single spinel structure in the Fd‾3 m (227) space group, and all five metal elements were uniformly distributed, demonstrating entropy stabilization. Meanwhile, the fabricated high-entropy ceramics manifest exceptional negative temperature coefficient (NTC) characteristics in the temperature range of 25 °C–350 °C. The aging stability is excellent as well. After aging at 150 °C for 1000 h, the ΔR/R0 of thick-film samples sintered at 1150 °C is less than 1 %. The successful synthesis of this novel class of spinel-type high-entropy ceramics introduces an emerging design approach for the development of NTC thermistors, particularly for applications in medium-temperature environments.

Online Noninvasive Technique for Condition Monitoring of Cooling System in Urban Rail Vehicles

The open self-ventilated cooling system is an important component to dissipate heat in urban rail vehicles. While after long term operation, the cooling system will deteriorate, which ultimately affects the reliable operation of traction converter. In this paper, we propose a method to monitor the health status of cooling system in urban rail vehicles using the temperature response curve of negative temperature coefficient (NTC) thermistor built in IGBT module. Back Propagation Neural Network (BPNN) is employed to predict the reference curve of healthy state under different working conditions and Discrete Fréchet Distance (DFD) algorithm is applied to achieve the difference comparison. The proposed approach considers the dynamic response process and is suitable for online monitoring. Advantages of the proposed approach include no need to install additional measurement circuit and to heat the module to thermal equilibrium. Moreover, this method enables the concurrent monitoring of multiple components in the cooling system. Simulation analysis and experimental tests are performed to verify the accuracy and effectiveness.