Negative Temperature Coefficient Thermistors Research Articles

Extremely enhanced thermal stability of Y2/3Cu3Ti4O12 ceramics by a Pechini method

AbstractY2/3Cu3Ti4O12 ceramic is a novel semiconductor with potential applications in electronic devices. However, its resistance drift and surface structure defects limit the application for negative temperature coefficient thermistor devices. A comparative study of solid‐phase and a Pechini processing of Y2/3Cu3Ti4O12 is presented in this paper, in the particular comparative study of stability. The Pechini method is found to be effective in lowering sintering temperature and improving thermal stability (ΔR/R0 < 0.3％) in comparison with solid‐phase method. The origin of the stability deterioration is related to the oxidation state of Cu ions and the migration of sublattice. The Pechini method overcomes stoichiometric ratio deviations and cation vacancy diffusion, thus reducing metal ion segregation in a continuous high‐temperature environment and thereby showing unique insensitivity to oxygen. The important role of the Pechini method in improving thermal stability is revealed, which is expected to be used in the preparation of high stability electron devices.

Reverse Offset Printed, Biocompatible Temperature Sensor Based on Dark Muscovado.

A reverse-offset printed temperature sensor based on interdigitated electrodes (IDTs) has been investigated in this study. Silver nanoparticles (AgNPs) were printed on a glass slide in an IDT pattern by reverse-offset printer. The sensing layer consisted of a sucrose film obtained by spin coating the sucrose solution on the IDTs. The temperature sensor demonstrated a negative temperature coefficient (NTC) with an exponential decrease in resistance as the temperature increased. This trend is the characteristic of a NTC thermistor. There is an overall change of ~2800 kΩ for the temperature change of 0 °C to 100 °C. The thermistor is based on a unique temperature sensor using a naturally occurring biocompatible material, i.e., sucrose. The active sensing material of the thermistor, i.e., sucrose used in the experiments was obtained from extract of Muscovado. Our temperature sensor has potential in the biomedical and food industries where environmentally friendly and biocompatible materials are more suitable for sensing accurately and reliably.

NiMn2O4 revisited: Temperature‐dependent cation distribution from in situ neutron diffraction and thermopower studies

AbstractThe cation distribution of the negative temperature coefficient (NTC) thermistor spinel NiMn2O4 was studied in the temperature range from 55 to 900°C, using a combined in situ neutron diffraction and thermopower study. Rietveld refinements of in situ neutron diffraction data reveal a temperature dependence of the degree of inversion with an inversion parameter of 0.70(1) at 900°C and 0.87(1) at 55°C. Thermopower measurements were evaluated using a modified Heikes formula, and the [Mn4+]/[Mn3+] ratio on octahedral sites of the spinel structure was calculated considering spin and orbital degeneracy. The inversion degree and disproportionation parameter, determined independently as function of temperature, were used to calculate the cation distribution of NiMn2O4 in the whole temperature range. At high temperature, within the stability range of the spinel, the cation distribution is characterized by a moderate degree of inversion with a concentration of = 0.71(2) and small tendency toward disproportionation with a high concentration of = 0.98(2). At 55°C, cation inversion is enhanced as illustrated by a large concentration of = 0.87(2), and a small = 0.24(2) content indicates extensive Mn‐disproportionation. Finally, conclusions regarding possible ageing mechanisms of this important NTC thermistor material are drawn.

Formation of a high stability NTC thick film by low-temperature sintering of Co2.77Mn1.71Fe1.10Zn0.42O8 ceramics containing Bi2O3-B2O3-SiO2-ZnO glass frits

In this paper, a new Pb-free negative temperature coefficient (NTC) thick film thermistor, based on Co 2.77 Mn 1.71 Fe 1.10 Zn 0.42 O 8 (CMFZ), containing Bi 2 O 3 -B 2 O 3 -SiO 2 -ZnO (BBSZ) glass frits were successfully fabricated using a spin coating technique. It is confirmed that the resistance of the samples, in the sintering temperature range of 850–1050 °C, generates significant changes due to the change in grain sizes. The room temperature resistance of thick film samples ranges from 118 kΩ to 370 kΩ, while the range of B 25/50 values is 4050–4225 K. Aging and analysis indicate that the appropriately increased sintering temperature enhances the stability of thick film samples. Based on the surface morphology, resistance consistency, and aging stability of the samples, the optimal sintering temperature was determined to be 1000 °C with the Δ R/R 0 less than 0.35% after aging at 125 °C for 700 h. These findings provide important guidance and significance for the development of the high stability thick film NTC thermistors at a lower sintering temperature. • Sintering temperature of thermistor can be reduced to 1000 °C after adding glass additives. • Aging drift rate of thick-film thermistor is less than 1% after 700 h of aging. • Sintering temperature is considered a key variable affecting aging stability. • Electrical properties are highly affected by sintering temperature.

Effect of Ce-doping on microstructure and electrical properties of LaAlO3 ceramics

A series of novel negative temperature coefficient (NTC) thermistor materials based on La1-xCexAlO3 (0 ≤ x ≤ 0.2) ceramics were synthesized via the solid-state route. X-ray diffraction results confirmed the successful doping of Ce in the La1-xCexAlO3 crystal and the formation of a good solid solution. Scanning electron microscopy results indicated that Ce doping is beneficial for grain growth and reduces the porosity of the samples. With the increase in the Ce doping amount, the average grain size increased from 2.1793 to 10.7344 μm, and densities of the ceramics increased from 93.15% to 99.26%. The temperature vs resistance curve indicated that Ce doping reduces the resistivity of LaAlO3 materials, while reducing the B200/1400 value of the LaAlO3 ceramic. For a doping amount of 0.2, the B200/1400 value of the LaAlO3 ceramic decreased from 18175.1 to 4897.7K, and the resistivity at 1000 °C decreased from 68971.87 to 1105.15 Ω cm. In addition, the La1-xCexAlO3 (0 ≤ x ≤ 0.2) series materials exhibited good linear NTC characteristics. X-ray photoelectron spectroscopy results revealed that the resistivity of the LaAlO3 materials decreased after Ce doping owing to the transformation between the Ce4+ and Ce3+ valence states，and the concentration of Ce3+ increased with the increase in the Ce doping amount. Ce3+ increases the concentration of oxygen vacancies, decreasing the resistance. Impedance analysis findings suggested that the resistance of the La1-xCexAlO3 (0 ＜ x ≤ 0.2) material mainly originates from the grain. These results indicate that Ce doping is an effective method to reduce the resistivity of LaAlO3. Consequently, La1-xCexAlO3 (0 ≤ x ≤ 0.2) is a promising material for NTC applications.

Thermistor string corrections in data from very weakly stratified deep-ocean waters

An important parameter for observational studies on dynamical variations of the ocean is temperature (T) which determines density variations together with salinity. While the achievement of high absolute accuracy of T-sensors is a formidable task, even the maintaining of high precision is difficult for any long-term deep-ocean observations. This is because the deep ocean is very weakly stably stratified in density, in which all the dynamics is covered by a range of about 0.001 °C. One requires high-resolution T-sensors with low noise levels and precisely calibrated. However, common Negative Temperature Coefficient (NTC) thermistor T-sensors have electronic drift causing a bias of temperature with time. The drift rate varies with temperature (change) and time (age) between 0.0002 and 0.001 °C wk−1 for T-sensors used here. A string of such T-sensors moored in the open-ocean for more than a month after calibration requires a drift-correction. When moored in the deep-ocean, a secondary correction is necessary even immediately after calibration. Secondary correction uses reference layers that are homogeneous to within 0.00005 °C over 100 m vertically plus an additional polynomial correction to remove remaining bias prior or after the reference date. Secondary correction may also involve pressure information on surface tides and mooring deflection. In this paper, secondary corrections are described for two cases of data. For one case from the West-Mediterranean varying temperature-density relationship and near-homogeneous conditions exist. The other is from hadal-deep instruments on a long mooring line in the Challenger Deep, Mariana Trench, affected by tidal flow. Nearby shipborne CTD-data are always needed to establish the temperature-density relationship and the background vertical temperature slope to which the moored T-sensor data are referenced. The stability of moored T-sensors is compared with that of temperature sensors of CTD.

CaMn0.05Zr0.95O3–NiMn2O4 composite ceramics with tunable electrical properties for high temperature NTC thermistors

A series of novel high temperature negative temperature coefficient (NTC) composite ceramics based on (1-x)CaMn0.05Zr0.95O3-xNiMn2O4 (x = 0, 0.1, 0.2, 0.3) were fabricated by using the solid-state method. The Rietveld refinement method and backscattered electron (BSE) image confirmed the absence of any other phase. The conduction mechanism of the composite ceramics was determined by analyzing the complex impedance and resistance-temperature characteristics, which could be related to the formation of a continuous Mn3+-O-Mn4+ network. The effect of spinel content on the high temperature stability was analyzed using aging tests. The ρ400°C, ρ700°C and B400/700 values of the NTC thermistors were determined to be 4.9 × 106–1.2 × 104, 1.4 × 105–0.8 × 103 Ω cm and 12739-5712 K, respectively. This indicated that the electrical properties could be tuned by adjusting the weight ratio of CaMn0.05Zr0.95O3 and NiMn2O4. The findings obtained in this study reveal that the composite NTC thermistor exhibits a good application potential at high temperatures and under harsh environments.

Optimizing the stability and electrical transport properties of CeNbO4+δ-based oxide ceramics by regulating oxygen ion content

CeNbO4+δ ceramics have attracted extensive research interest because of their unique mixed ion-electron transport characteristics and interesting structure-functional characteristics caused by the difference in oxygen ion content. Although the change of oxygen ion content brings rich redox properties, it also causes serious crystal transformation and abnormal electrical transport properties. In order to obtain stable structure and excellent electrical transport properties, the directional regulation of the oxygen ion content has been realized through introducing Al2O3 and high temperature aging. After 600 h of aging at 1073 K, the prepared composite ceramics not only obtain a stable structure without crystal transformation, but also show good negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K–1273 K, in which the linear fitting maximum Pearson's r of the relationship between lnρ and 1000/T can reach 99.97%. The proposed method provides a new thought for the design and application of high-temperature electronic ceramics.

Design of a multi-channel high precision wearable temperature collection system based on negative temperature coefficient thermistor

<p>Body temperature is often used to screen infectious diseases and monitor treatment. Through the method of measuring the resistance of constant voltage temperature measuring circuit, a wearable multi-point body temperature monitoring system is researched and designed to determine skin surface temperature. The STM32F103C8T6 chip is used as the core processor, and the negative temperature coefficient thermistor (NTC) as the temperature sensing component. ADS1256 chip is a temperature signal conditioner, Bluetooth module is a wireless transmission unit, and LABVIEW is used to design the host computer interface. The constant voltage bridge circuit composed of thermistor and resistor voltage divider to carry out the acquisition of 8 channels of temperature data, and the 24bits ultra-high-precision analog-to-digital conversion module is configured with differential inputs to amplify, filter and convert analog signals; the converted data is processed and calculated in the single-chip microcomputer; finally, the data is transmitted to the host computer via Bluetooth. The thermistor is linearly compensated using the fourth-order formulation of the Stein-hart formula. Reduce the impact of environmental interference and uneven body temperature distribution from software and hardware. The error during the temperature measurement of temperature sensor is analyzed. The experimental results showed that the resolution of measurement system reached 0. 01 , and the temperature measurement accuracy was up to ± 0. 02 . This design scheme has high stability and accuracy; and the circuit is simple in structure, small in size, and low power consumption which can be used in occasions requiring precise body temperature measurement.</p>

Application and comparison of thermistors and fiber optic temperature sensor reference for ILP measurement of magnetic fluids in double cell magnetic hyperthermia

One of the simplest way to characterize the heating efficiency of magnetic fluids used in hyperthermia treatment is the calorimetric measurement of the specific loss power with direct temperature detection. However, the performance of metallic sensors in an alternating magnetic field is degraded by the self-heating of the probes, and electromagnetic interference can be also significant. In our double cell differential thermometric system these disturbing effects can be compensated. Specific loss power measurements of EMG700 magnetic fluid with negative temperature coefficient thermistors in differential configuration are presented, and control measurements were performed with an optical fiber thermometer in f=470kHz–1020kHz frequency and H=0.13kAm−1–1.19kAm−1 magnetic field strength range. We found that the specific loss power is proportional to the frequency and shows a quadratic dependence on the field strength in the low field strength region, therefore we calculated the intrinsic loss power of the fluid from the measured specific loss power. At this field conditions intrinsic loss power up to 0.53nHm2kg−1 was determined.

Preparation and sealing effects of Mg–Al–Si–Ba–O-based glass-ceramic coatings on NTC thermistors

Herein, Mg–Al–Si–Ba–O-based glass ceramics were studied as potential candidates to protect Mn–Co–Ni–O-based negative temperature coefficient (NTC) thermistors at high temperatures such as 900 °C. The ceramics were prepared in three glass formulations (1#: 15MgO–15Al2O3-44.7SiO2–25BaO, 2#: 17MgO–17Al2O3–41SiO2–25BaO and 3#: 17MgO–17Al2O3–41SiO2–20BaO–5Y2O3 (in mol%)) and their glass-transition temperatures (Tg) were determined using the differential scanning calorimetry (DSC) method. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the parent glasses and glass-ceramic coatings. The sealing effects of the glass ceramics were examined by conducting an insulation test. The glass-ceramic sealing structures were subjected to 1000 thermal shock cycles at temperatures varying from room temperature to 900 °C. Notably, the sealing structure of glass-ceramic coating 1# was compact at a Tg of 760.9 °C. The glass-ceramic coatings effectively maintained the NTC properties of the sensitive ceramics in all three formulations. Interestingly, the glass-ceramic coating 3# containing Y2O3 demonstrated an increase in electrical resistance. Both the NTC thermistors coated with 1# and 2# glass formulations successfully passed 1000 thermal shock cycles without visible failures, and their resistance change ratios were well below the requisite 20%.

Resonant acoustic-mixing technology as a novel method for production of negative-temperature coefficient thermistors

Resonant acoustic-mixing technology as a novel method for production of negative-temperature coefficient thermistors

Novel NTC ceramics based on pyrochlore-type A2Ti2O7 (A = Sm, Eu, Y) titanates for high-temperature thermistors

In this study, a series of novel negative temperature coefficient thermistor materials based on A2Ti2O7 (A = Sm, Eu, Y) titanate ceramics have been developed for high-temperature applications. The A2Ti2O7 (A = Sm, Eu, Y) ceramics showed cubic pyrochlore structures with dense morphology in X-ray diffraction and scanning electron microscopic analyses. These ceramics showed typical NTC characteristics in a wide temperature range of 673–1473 K, accompanied by resistance drift rates of 2.71%, 1.63%, and 4.95% for 400 h of ageing at 1173 K. The proposed ceramics have high resistivity and thermal constants B that ensure their better sensitivity at high temperatures and also show unique oxygen insensitivity. These properties outperform those of traditional high-temperature NTC materials composed of perovskite-type or scheelite-type ceramics, making A2Ti2O7 (A = Sm, Eu, Y) ceramics promising candidates for fabricating high-temperature NTC thermistors.

Nickel oxide-based flexible thin-film NTC thermistors by using reverse offset printing

In recent years, the use of printing methods to fabricate electronic devices (printed electronics) has attracted attention because of their low cost and low environmental impact. Printing technology enables the high-throughput fabrication of electrical circuits on film substrates, thereby providing inexpensive personal healthcare devices to monitor health status in real-time, for example. Temperature detection is one of the central concerns as a fundamental physical quantity in various fields. In 2013, a highly sensitive flexible thermistor was reported by formulating aqueous inks of nickel oxide (NiO) nanoparticles for inkjet printing. However, it required a high-temperature calcination process of more than 200 °C, which led to the use of expensive polyimide films with high heat resistance. It is necessary to promote further the development of low-temperature processes for printed thermistors to realize flexible negative temperature coefficient (NTC) thermistors at low cost using printed electronics technology. Moreover, in screen printing and inkjet printing, the definition of the ink pattern applied on the substrate changes due to spreading and coffee distortion phenomena, and the thickness between sensors becomes non-uniform, which is a structural consistency problem that can lead to variations in sensing performance. Therefore, in this study we developed low-temperature processable printed NTC thermistors with a temperature-sensitive layer of NiO by using reverse offset printing. The NTC thermistors were fabricated by printing a comb-like pattern of silver nanoparticles and a thin NiO film. In addition, the low-temperature formation of a NiO layer by oxygen plasma treatment was investigated, and x-ray photoelectron spectroscopy was used to carry out compositional analysis of the surface. Together with the plasma-assisted calcination, a flexible NTC thermistor formed on polyethylene terephthalate film is demonstrated.

A novel MnCoNiCuZnO5 complex-phase ceramic for negative temperature coefficient thermistors

High-entropy oxides have received a lot of attention from domestic and foreign researchers because of their simple structure and excellent property. Based on the idea of high entropy composition, we designed and synthesized a novel thermistor material, MnCoNiCuZnO5 in this work. The oxide contains a complex phase structure, consisting of a cubic spinel structure and a rock-salt structure. The complex-phase ceramic, compared with other Cu-containing oxides, exhibits high thermal stability. The aging coefficient (ΔR/R0) of the complex-phase ceramic reaches 1.16% at 125 °C for 800 h, which can be ascribed to the stabilizing effect of entropy. The successful fabrication of this complex-phase ceramic opens a new route to enhance the thermal stability of the material.

Variation of annealing temperature with excess of NaOH concentration on Ag2S synthesis from argentometry titration waste as NTC thermistor

Utilization of AgCl from argentometric titration waste can be done by converting AgCl into silver sulfide (Ag2S) semiconductor. The variation of annealing temperature in Ag2S synthesis affects the properties and quality of the Ag2S semiconductor. Silver sulfide semiconductor can be applied as a NTC (negative temperature-coefficient) thermistor temperature sensor. The NTC thermistor shows a decrease in resistance with increasing temperature. This study aims to synthesize Ag2S from argentometric titration waste with excess NaOH concentration and variations in annealing temperature as a temperature sensor for NTC thermistors. Ag2S was synthesized using thiourea reagent in alkaline NaOH medium. The synthesized silver sulfide was then annealed at various temperatures of 100, 200 and 300 °C for 30 min. Ag2S was then characterized using Thermo Gravimetrical Analysis (TGA), X-Ray Diffraction (XRD) and UV–Vis Diffuse Reflectance Spectroscopy (UV–Vis DRS). The results of TGA analysis showed that Ag2S at a temperature of 836 °C had decomposed into Ag and S2. From the XRD characterization results showed the presence of Ag2S at 2θ peaks of 22; 29; 31; 38 and 41°. Ag2S crystal size increases with increasing annealing temperature, which are 37.04; 39.55 and 41.68 nm. The results of UV–Vis DRS characterization showed that the Ag2S band gap value decreased with increasing annealing temperature, which were 0.96; 0.94; and 0.92 eV. The resistance measurement results show that the Ag2S semiconductor at annealing temperature of 300 °C is an NTC thermistor with good electrical quality, has a sensitivity of 6.85% and a thermistor constant of 6087 K.

Improved Temperature Monitoring and Protection Method of Three-Level NPC Application Based on Half-Bridge IGBT Modules

The overheating stress of power devices is the main cause of converter system failures, so real-time temperature acquisition, as well as timely over-temperature protection, under various operating conditions are key to achieving a more reliable energy conversion. In this paper, an improved three-dimensional (3-D) coupled thermal model for insulated gate bipolar transistors (IGBTs) and related heatsink is constructed by considering the thermal coupling effects at both the device- and the module level. Furthermore, the coupled thermal impedance parameters are thereby extracted based on the finite-element method (FEM), so that the dynamic loss and transient temperature distribution under actual working conditions can be obtained based on this electro-thermal coupling model. Meanwhile, to avoid the overheating damage of power devices due to untimely action of the negative temperature coefficient (NTC) thermistor over-temperature protection, this article aims at the idle IGBT device in the three-level neutral-point clamped (NPC) application using IGBT half-bridge modules, combined with the emitter terminal temperature, and finally realizes the multiple over-temperature protection settings. The improved temperature monitoring methods proposed in this paper are realized by the drive and control circuits and verified through simulation and experimental results.

Deep Neural Network Based Linearization and Cold Junction Compensation of Thermocouple

In this proposed work, temperature sensors, namely, a thermocouple and thermistor were linearized using deep neural networks. The deep feedforward neural network (DFNN) technique was proposed to linearize the K-type thermocouple’s output, in the given temperature range −100 °C to 1372 °C, while nonlinearity was reduced from 2.03% to 0.002% full scale span (FSS). Deep layer recurrent neural network (DLR-NN) was used to reduce the nonlinearity of a negative temperature coefficient (NTC) thermistor from 84.63% to 0.13% FSS. The linearized thermistor was used for cold junction compensation (CJC) of the thermocouple. In both the thermocouple and thermistor, linearization was achieved in a single stage for a wide range digitally using deep neural networks alone. There were no analog pre-signal conditioning circuits, unlike the existing neural network-based linearization techniques in literature. A hardware setup of a stand-alone module for linearization was designed using the Raspberry pi microcontroller consisting of two soft modules, one for thermocouple linearization and the other for thermistor linearization. The proposed system was experimentally tested using a K-type thermocouple on a thermal calibrator in a 0 °C–300 °C range. The cold junction compensated output of the thermocouple had a maximum absolute error of 0.34 °C when ambient temperature varied from 0 °C to 40 °C. The results were satisfactory and better than the existing National Institute of Standards and Technology (NIST) standard. This linearization technique can be extended to other thermocouple types as well as other nonlinear sensors.

Tailoring the properties of Ni-Mn based NTC thermistors by Cu and Li addition

The influence of Cu and Li doping in the structural and R-T characteristics of Ni-Mn-based spinel oxide negative temperature coefficient (NTC) thermistors prepared using the conventional solid-state synthesis method was investigated in this study. The doping of Cu and Li in nickel manganite plays an important role in tailoring the thermistor parameters. The structural characterization of the prepared samples using XRD revealed that the basic structure of the samples is not altered by the addition of the dopants Cu and Li. The particle size of the samples was obtained at less than 50 nm. R-T characteristics showed a decrease in resistance with temperature. It was observed that the addition of dopant Cu in a minimal amount helps to tune the resistance of the thermistor in the required range and Li addition, as a dopant, stabilized the thermistor parameters B and alpha.

Cu-Mn Co-doped NiFe2O4 based thick ceramic film as negative temperature coefficient thermistors

NTC (Negative Temperature Coefficient) thermistors are widely used as temperature sensors in industrial and medical applications due to their high-temperature sensitivity, durability, and low cost. Generally, NTC thermistors are made from spinel structured ceramics formed by transition metal oxides with the general formula AB2O4. One of the spinel structured ceramics that can be made for NTC thermistors is NiFe2O4 nanoparticles. This work aimed to prepare Cu-Mn co-doped NiFe2O4 based thick ceramic film using Jarosite mineral as a precursor. The synthesis method used was a simple coprecipitation method, while the technique used in making a thick ceramic film was a simple screen printing technique. The sintering temperatures used were 1000 °C, 1100 °C, and 1200 °C. Based on x-ray diffraction analysis, the thick films consist of spinel phase, hematite phase, and some unidentified phase. The constant thermistor values (B) for thick films obtained with 1000, 1100, and 1200 °C sintering temperatures were 4740 K, 5669 K, and 5731 K, respectively. These results showed that all obtained thick films had passed the minimum value in market needs (B ≥2000 K).