Maximum Temperature Coefficient Research Articles

MoS2high temperature sensitive element with a single Si3N4protective layer.

Temperature sensors find extensive applications in industrial production, defense, and military sectors. However, conventional temperature sensors are limited to operating temperatures below 200°C and are unsuitable for detecting extremely high temperatures. In this paper, a method for thermal protection of molybdenum disulfide (MoS2) films is proposed and a MoS2 high temperature sensor is prepared. By depositing a monolayer of Si3N4 onto MoS2, not only is the issue of high-temperature oxidation effectively addressed, but also the contamination by impurities that could potentially compromise the performance of MoS2 is prevented. Moreover, the width of the Schottky barrier of metal/MoS2 is reduced by using PECVD deposition of 400 nm Si3N4 to form an ohmic contact, which improves the electrical performance of the device by three orders of magnitude. The sensor exhibits a positive temperature coefficient measurement range of 25 to 550°C, with a maximum temperature coefficient of resistance (TCR) of 0.32%·°C-1. The thermal protection method proposed in this paper provides a new idea for the fabrication of high-temperature sensors, which is expected to be applied in the high-temperature field.&#xD.

Study on heat transfer characteristics and enhancement mechanism of supercritical carbon dioxide in adaptive channels

Supercritical CO2 power cycles have promising applications in many fields, the heat transfer of supercritical CO2 is critical to the efficiency and safe operation of cycle system. The adaptive channel was previously proposed by our group to improve heat transfer of supercritical CO2, the performance of heat exchanger with adaptive channel was experimentally studied. Whereas the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism remain unclear. In this study, the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism are analyzed numerically based on a single channel, the effect of structure on heat transfer is analyzed through the maximum wall temperature and average heat transfer coefficient under the same length and heat transfer area. The results reveal adaptive channel is effective at alleviating heat transfer deterioration with no local peak in wall temperature distribution. The channel variation length of adaptive channel need to be increased from 0.4 to 0.8 with the aggravation of heat transfer deterioration in order to eliminate local wall temperature peak. For the heat transfer deterioration conditions, the maximum wall temperature lowers first and then increases as channel variation length increases, there is a length that makes the maximum wall temperature lowest, which is lowered by more than 40 °C compared with straight channel. The average heat transfer coefficient can be increased by 1.1 ∼ 1.5 times as channel variation length increases. For the no heat transfer deterioration conditions, the maximum wall temperature increases about 30 °C whereas average heat transfer coefficient can be increased by 58 %∼76 % with channel variation length increasing. The mechanism of adaptive channel alleviating heat transfer deterioration is as follows: the fluid velocity always presents an inverted U-shaped distribution along the radial direction in adaptive channel, the radial density difference is less and buoyancy effects heat transfer weakly. The turbulent kinetic energy is kept at high, so the heat near the wall is transferred to the main flow timely.

Effects and mechanism of thermal insulation materials on thermal runaway propagation in large-format pouch lithium-ion batteries

The large heat transfer area of large-format lithium-ion batteries primarily facilitates conduction heat, which is responsible for triggering the thermal runaway of adjacent cells. Therefore, the primary consideration is to utilize thermal insulation materials between cells in order to slow down or prevent the process of thermal runaway propagation. In this study, three varieties of thermal insulation materials were employed to insulate individual cells within a module comprising three large-format pouch cells. These materials include pre-oxygenated wire aerogel (AG-ST-POF), polymer-coated pre-oxygenated wire aerogel (PC-AG-ST-POF), and silicone (SI). The study experimentally examined the thermal runaway propagation (TRP) behavior of the battery module under conditions without insulation materials and with various types of insulation materials. The impact of thermal insulation materials on the TRP among cells was analyzed. The study revealed that none of the three materials completely suppressed the propagation of thermal runaway, although they did impede its progress. The overall impact of AG-ST-POF surpassed that of SI and PC-AG-ST-POF. Furthermore, the mechanism by which thermal insulation materials influence TRP was explored. The results of the thermophysical properties testing suggest that evaluating the impact of materials on TRP solely through thermal conductivity is not a reliable approach. Alternatively, the maximum service temperature and thermal diffusion coefficient are critical parameters for the selection of thermal insulation materials. This study can provide a valuable reference for process engineering design and application in the context of lithium-ion batteries, with the aim of mitigating the risk of TRP.

Study on heat transfer performance of cold plate with grid channel

The utilization of cold plate radiators as a prevalent method for indirect liquid cooling has been extensively investigated and implemented in server cooling systems. However, there is a lack of comprehensive study on the application of this technology at the chip size, indicating a need for more development and exploration in this area. A proposal was made for a grid-channel chip cold plate heat sink to facilitate the dissipation of heat from a chip. tests were conducted to investigate the impact of the flow rate of the cold plate and the layout of the inlet and outlet on various thermal parameters, including the average temperature, maximum temperature, thermal resistance, and uniformity coefficient of the cold plate. The tests were specifically conducted under a chip power of 150W, and the accuracy of the simulation was confirmed through the use of FLUENT. The findings indicate that the cold plate effectively regulates the temperature of the chip, ensuring it remains below 85 °C throughout all experimental groups. In contrast to the single in single out configuration, the single-in multiple-out layout exhibits a higher degree of temperature uniformity within the cold plate. Nevertheless, it is important to note that augmenting the quantity of exits does not guarantee an improvement in heat transfer efficiency. This outcome is contingent upon the presence of a longitudinal flow channel shared by the outlet and intake, as well as the dispersion characteristics of the outlet. Enhancing the dispersion of the exit can significantly enhance the thermal transfer efficiency of the cold plate. Furthermore, a strategy for adjusting the aperture of the orifice is proposed as a solution to address the challenges related to flow uniformity and the issue of high pressure drop in the cold plate.

Elaboration of La (Sr/Na) Mn (Ti) O3 ceramic, structural, and morphological investigations, and contribution of direct and indirect interactions on transport properties

The charge carrier's dynamics of La0.7(Sr5/6Na1/6)0.3Mn0.7Ti0.3O3 (LSNMTO) ceramic is conducted using the temperature and frequency dependences of the electrical conductivity and their scaling formalisms. The structural study indicates that LSNMTO crystallizes in a rhombohedral R3‾c perovskite structure with no detectible secondary phases. A phase transition from the high-temperature metallic behavior to the low-temperature semiconductor nature is observed from the electrical conductivity curve at TS-M = 415 K. Further, it is observed that the cation-anion-cation and the cation-cation interactions are present in the material, and play important role in governing the electrical behaviors of LSNMTO. From 200 K to 415 K, the Non-adiabatic Small Polaron Hopping is the predominant conduction process, although the Mott-Variable Range Hopping mechanism governs the conductivity at low temperatures. In the intermediate temperature range, the dynamic of the charge carriers is explained using the Shklovskii Efros model. The frequency-activated conductivity obeyed the universal laws (double-Jonscher and Jonscher laws). At high frequencies, the dispersion of the conductivity spectra is attributed to the presence of hopping and tunneling conduction processes. The Time-Temperature Superposition Principle (TTSP) is obeyed over a large temperature range from 160 K to 350 K. Below 160 K, the deviation from the TTSP is attributed to the coexistence of hopping and tunneling conduction mechanisms. Deviations from the Summerfield scaling and shifts of the isotherms to higher values on decreasing the temperature are due to the local structural disorder in LSNMTO. Therefore, the structural particularities of LSNMTO can result in diverse conduction pathways giving an increase to the deviations from the Summerfield scaling. The studied ceramic exhibits a very motivating maximum negative temperature coefficient of resistance NTCR = −13.36% which is significantly elevated as compared to previously investigated compounds.

Phytoplankton thermal trait parameterization alters community structure and biogeochemical processes in a modeled ocean.

Phytoplankton exhibit diverse physiological responses to temperature which influence their fitness in the environment and consequently alter their community structure. Here, we explored the sensitivity of phytoplankton community structure to thermal response parameterization in a modelled marine phytoplankton community. Using published empirical data, we evaluated the maximum thermal growth rates (μmax ) and temperature coefficients (Q10 ; the rate at which growth scales with temperature) of six key Phytoplankton Functional Types (PFTs): coccolithophores, cyanobacteria, diatoms, diazotrophs, dinoflagellates, and green algae. Following three well-documented methods, PFTs were either assumed to have (1) the same μmax and the same Q10 (as in to Eppley, 1972), (2) a unique μmax but the same Q10 (similar to Kremer etal., 2017), or (3) a unique μmax and a unique Q10 (following Anderson etal., 2021). These trait values were then implemented within the Massachusetts Institute of Technology biogeochemistry and ecosystem model (called Darwin) for each PFT under a control and climate change scenario. Our results suggest that applying a μmax and Q10 universally across PFTs (as in Eppley, 1972) leads to unrealistic phytoplankton communities, which lack diatoms globally. Additionally, we find that accounting for differences in the Q10 between PFTs can significantly impact each PFT's competitive ability, especially at high latitudes, leading to altered modeled phytoplankton community structures in our control and climate change simulations. This then impacts estimates of biogeochemical processes, with, for example, estimates of export production varying by ~10% in the Southern Ocean depending on the parameterization. Our results indicate that the diversity of thermal response traits in phytoplankton not only shape community composition in the historical and future, warmer ocean, but that these traits have significant feedbacks on global biogeochemical cycles.

Experimental study for artificial neural network modeling on thermal and flow performances of electric traction motor with oil spray cooling

The oil spray cooling is emerging as advanced thermal management technique for next generation electric traction motor. The performance of oil spray cooling needs to be mapped and predicted based on various influential factors to develop efficient thermal management system for electric traction motors. In the present work, the thermal and flow performances are experimentally investigated and predicted using an artificial neural network (ANN) for electric traction motor with oil spray cooling. The thermal and flow performances are extracted in terms of maximum temperature, heat transfer coefficient, Nusselt number, spray pressure and spray power consumption. The effects of nozzle types, spray heights, volume flow rates and chiller temperatures are analyzed as operating factors. The ANNs are modeled considering Levenberg-Marquardt (LM) training variant, 10 hidden neurons and Tangential-sigmoidal (Tan) and Logarithmic-sigmoidal (Log) as transfer functions. The thermal and flow performances are superior for full cone followed by hollow cone and spiral nozzles in decreasing order. The higher spray height, higher volume flow rate and lower chiller temperature show optimum values of maximum temperature and heat transfer coefficient. The spray power consumption is maximum in case of higher volume flow rate, reported less variation with change in spray height and chiller temperature. The ANN model comprising of LM-Tan algorithm is recommended as the best model with prediction error within ±1% for all thermal and flow performances. The predicted results from the optimum ANN model are validated with experiments with maximum coefficient of determination (R2) and coefficient of variance (COV) as 0.99 and 3.20, respectively. The correlations for thermal and flow performances in terms of all influential factors are proposed using the optimum ANN model.

DC conductivity mechanism in La0.7Sr0.3MnO3 (LSMO)-ZnO nanocomposites

La0.7Sr0.3MnO3 (LSMO)-ZnO nanocomposites with varying concentrations of ZnO have been synthesized using the solution combustion method. A bimodal particle size distribution has been formed in all the samples. The crystallite size increases in the composites as compared to LSMO. The study on electrical resistivity reveals that LSMO exhibits a metal-to-insulator transition at 359 K, while the inclusion of ZnO suppresses the metallic behavior in the composites and increases the resistivity. Transport behavior of the samples in metallic and semiconducting regions has been explained with a known polynomial equation and a two-channel conduction model obeying the small polaron hopping mechanism, respectively. A very low activation energy in the range of 10–12 meV is observed due to smaller-sized particles. The presence of ZnO drives the hopping mechanism from adiabatic in LSMO to become non-adiabatic in the composites and enhances the maximum temperature coefficient of resistance. 80% LSMO-20% ZnO (by weight ratio) composite shows a maximum TCR of −29.81%/K at 248 K, which makes it a potential candidate for several applications in sensing devices. The Curie temperature of the material decreases with the increase in ZnO content in the sample. The results of this study also confirm the existence of correlation between the electrical and magnetic properties of LSMO.

Assessment of Newly-Designed Hybrid Nanofluid-Cooled Micro-Channeled Thermal Management System for Li-Ion Battery

Abstract Maintaining both maximum temperature and temperature uniformity within the desirable limit is a crucial issue for high C-rating Li-ion batteries of electric vehicles, which can be achieved by the properly designed battery thermal management system (BTMS). In this research, three new designs of liquid-cooled micro-channeled BTMS are suggested for cylindrical batteries to address the issue of temperature variations and uneven temperature distribution. Using 3D numerical simulation, we investigate the impacts of volume flowrate and the usage of mono/hybrid nanofluids with varying concentrations on the thermal performance of the battery pack at a high C-rate by utilizing a two-phase mixture model. Effects on maximum temperature, temperature uniformity, pumping power, and heat transfer coefficient to pressure drop ratio are investigated. Results demonstrate that the effectiveness of heat transmission and temperature uniformity of the battery pack are positively impacted by an increase in nanoparticle concentration in nanofluid and volume flow rate. Even at high C-rates (5 C), the proposed design can effectively reduce both cell temperature and thermal gradient of the 21700-type cylindrical cell. Design 3 is the most favorable BTMS for Li-ion cylindrical battery in terms of both maximum temperature and temperature uniformity (maximum temperature of 304.72 K and temperature difference of 4.7 K).

Experimental Study on Dielectric Fluid Immersion Cooling for Thermal Management of Lithium-Ion Battery

The rapidly growing commercialization of electric vehicles demands higher capacity lithium-ion batteries with higher heat generation which degrades the lifespan and performance of batteries. The currently widely used indirect liquid cooling imposes disadvantages of the higher thermal resistance and coolant leakage which has diverted the attention to the direct liquid cooling for the thermal management of batteries. The present study conducts the experimental investigation on discharge and heat transfer characteristics of lithium-ion battery with direct liquid cooling for the thermal management. The 18,650 lithium-ion cylindrical battery pack is immersed symmetrically in dielectric fluid. The discharge voltage and capacity, maximum temperature, temperature difference, average temperature, heat absorbed, and heat transfer coefficient are investigated under various conditions of discharge rates, inlet temperatures, and volume flow rates of coolant. The operating voltage and discharge capacity are decreasing with increase in the volume flow rate and decrease in the inlet temperature for all discharge rates. At the higher discharge rate of 4C, the lowest battery maximum temperatures of 60.2 °C and 44.6 °C and the highest heat transfer coefficients of 2884.25 W/m2-K and 2290.19 W/m2-K are reported for the highest volume flow rate of 1000 mLPM and the lowest inlet temperature of 15 °C, respectively.

Study on the three-dimensional heat flow field of supercritical nitrogen in a micro-channel plate heat exchanger

Micro-channel plate heat exchanger (MCPHE) has been recognized as a new high-efficiency heat transfer device and widely utilized in the energy field due to its compactness and high heat exchange rate. In this paper, the three-dimensional heat flow field of supercritical nitrogen (SCN2) in a simplified MCPHE is numerically simulated using computational fluid dynamics (CFD) simulation technology. The numerical approach predicts the thermo-hydraulic performance of SCN2 with a relatively good accuracy, by comparing with the published experimental data. Furthermore, the effects of pressure (3.6 ∼ 7 MPa) and mass flux (800 ∼ 1200 kg/(m2∙s)) on the convective heat transfer characteristics of SCN2 are thoroughly examined, especially the heat flow field of SCN2 in different circumferential directions of the micro-channel is revealed. The obtained results show that under the condition of low pressure and high mass flux, the maximum circumferential inner wall temperature appears at 90° of the micro-channel at the same axial position. With an increased mass flux, the maximum inner wall temperature and minimum heat transfer coefficient gradually shifts from 180° to 90°. When the buoyancy coefficient Gr*/Re2 > 1, the buoyancy force is conducive to enhance the fluid heat transfer capacity gathered at the bottom of the micro-channel. Meanwhile, the buoyancy force could make the distribution of thermo-physical properties of SCN2 uneven at the same time. Finally, in view of the obtained data, a new dimensionless correlation is proposed to predict the convective heat transfer process of SCN2 inside MCPHE, and the prediction error is less than 20%. The research outcomes could provide a reference for the optimal design and safe operation of MCPHE.

Germanium nanowire microbolometer

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in the μm range, limiting miniaturization for future highly integrated ‘More than Moore’ concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of −0.07 K−1 at T = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

Ferrofluidic thermal switch in a magnetocaloric device

SummaryThermal switches are advanced heat-management devices that represent a new opportunity to improve the energy efficiency and power density of caloric devices. In this study we have developed a numerical model to analyze the operation and the performance of static thermal switches in caloric refrigeration. The investigation comprises a parametric analysis of a realistic ferrofluidic thermal switch in terms of the maximum temperature span, cooling power, and coefficient of performance. The highest achieved temperature span between the heat source and the heat sink was 1.12 K for a single embodiment, which could be further developed into a regenerative system to increase the temperature span. A sensitivity analysis is conducted to correlate the relationship between the input parameters and the results. We show that thermal switches can be used in caloric devices even when switching ratios are small, which greatly extends the possibilities to implement different types of thermal switches.

Temperature affects the oxidation kinetics of co-cultured Nitrobacter winogradskyi and Nitrobacter hamburgensis in nitrite-oxidizing bioreactor

Nitrobacter is an important chemolithoautotrophic nitrite-oxidizing bacteria and has exhibited potential for the oxidation of nitrite to nitrate in natural and engineered ecosystems. Microbial kinetics of Nitrobacter have been widely reported and are used to model the nitrite oxidation process and optimize the design parameters of the biological processes for wastewater treatment. However, limited information is available about the nitrite oxidation kinetics of the two coexisting Nitrobacter stains, namely the Nitrobacter winogradskyi and the Nitrobacter hamburgensis. The current work mainly focuses on the influence of temperature on the kinetic characteristics of the coexistence of N. winogradskyi and hamburgensis, which were enriched in a lab-scale sequencing batch reactor (SBR) through 419 operating cycles. The results for the kinetic properties of nitrite oxidation of the enrichments within the temperature range of 15–35 °C showed that the maximum specific rate (rmax), half-saturation coefficients (KS), growth-rate constants (μmax), and temperature coefficient (θ) lied within the ranges of 22.91–93.58 mM/g/d, 0.13–2.47 mM, 0.026–0.105 1/d, and 1.038–1.137, respectively. The maximum activity and nitrite affinities of tested microorganisms were sensitive to temperature. Furthermore, the relationships between temperature and normalized kinetic parameters (rmax, μmax, and θ) were developed as: 0.069T − 0.076 (15–30 °C), 0.0057T − 0.062 (15–30 °C), and 5.7T40.9+T+T210.5 (15–35 °C), respectively. Moreover, the capabilities of N. winogradskyi and N. hamburgensis to oxidize nitrite were lost at the temperature of 35 °C and were non-recoverable at temperature of 25 °C. Overall, the findings of the present work can provide available data for future study about the mathematic models of nitrification kinetics and ecological niche differentiation of Nitrobacter species.

Investigation of temperature coefficients of PV modules through field measured data

Varying broadband irradiance and temperature are generally known as the major factors influencing the performance of PV modules, but studies have also shown the substantial impact of spectral variations. In this work, a simple and efficient method to calculate the temperature coefficient using long term data is demonstrated. Temperature coefficients of PV modules are estimated from long term performance data following IEC 60891 standard with additional spectral correction, and are compared against the datasheet values. Significant improvement of correlation coefficient from −0.89 to −0.97 is observed during the regression for maximum power temperature coefficient of two poly-crystalline modules, after spectral correction by spectral factor (SF). Also, the standard deviation of yearly estimated values of these coefficients reduced from 5–7 % to 1–2 %. In another setup involving spectral measurements and various PV technologies, the annual mean of 1.62 eV for average photon energy in 350–1700 nm range, suggests a general blue shift of the spectrum. Higher averages than reference values of useful fraction (UF) for c-Si, CIGS and HIT technologies also validate the blue shift of spectrum. Results show SF produces maximum power temperature coefficients closer to the datasheet values compared to UF, suggesting better applicability of SF as an index for spectral correction. The coefficient values were found closer to STC values and the results from Mann and Kendall test, employed to detect any underlying monotonic trend in the development of temperature coefficients over eight years, showed no increasing or decreasing trend and hence no degradation of temperature coefficients for the long-term exposed PV modules.

Potentiometric Performance of a Highly Flexible-Shaped Trifunctional Sensor Based on ZnO/V2O5 Microrods.

A trifunctional flexible sensor was fabricated on a polyethylene terephthalate (PET) fiber surface. Synthesized ZnO and ZnO/V2O5 composite were coated on ZnO seed layer sputtered PET fiber. X-ray diffraction (XRD) and photoelectron spectroscopy (XPS) techniques confirmed the exact formation of ZnO and ZnO/V2O5. The fabricated ZnO/V2O5 on ZnO seeds base temperature sensor recorded better electrical properties and reversibility with a maximum temperature coefficient resistance (TCR) of 0.0111 °C−1. A calibration curve (R = 0.9941) within glucose concentration of (10 µM–10 mM) was obtained at +0.8 V vs. Ag/AgCl from current-voltage curves which assisted in calculating glucose sensitivity, limit of detection (LOD), limit of quantification (LOQ). The electrode achieved an outstanding performance of sensitivity (72.06 µAmM−1cm−2), LOD (174 µM), and LOQ (582 µM) at optimum deposition time. Interference from oxidation of interfering biomolecules such as ascorbic acid, dopamine, and uric acid were negligible compared to glucose. Finally, the fabricated electrode was employed as a pH sensor and displayed a pH sensitivity of 42.26 mV/pH (R = 0.9922). This fabricated ZnO/V2O5 electrode exhibited high sensitivity and a stable combined temperature, glucose, and pH sensor which is promising for development of multifunctional sensors in next generation wearables.

A low‐power native NMOS‐based bandgap reference operating from −55°C to 125°C with Li‐Ion battery compatibility

SummaryThe paper describes the implementation of a bandgap reference based on native‐MOSFET transistors for low‐power sensor node applications. The circuit can operate from −55°C to 125°C and with a supply voltage ranging from 1.5 to 4.2 V. Therefore, it is compatible with the temperature range of automotive and military‐aerospace applications, and for direct Li‐Ion battery attach. Moreover, the circuit can operate without any dedicated start‐up circuit, thanks to its inherent single operating point. A mathematical model of the reference circuit is presented, allowing simple portability across technology nodes, with current consumption and silicon area as design parameters. Implemented in a 55‐nm CMOS technology, the voltage reference achieves a measured average (maximum) temperature coefficient of 28 ppm/°C (43 ppm/°C) and a measured sample‐to‐sample variation within 57 mV, with a current consumption of 420 nA at 27°C.

Study on the Stability of the Electrical Connection of High-Temperature Pressure Sensor Based on the Piezoresistive Effect of P-Type SiC.

In this study, a preparation method for the high-temperature pressure sensor based on the piezoresistive effect of p-type SiC is presented. The varistor with a positive trapezoidal shape was designed and etched innovatively to improve the contact stability between the metal and SiC varistor. Additionally, the excellent ohmic contact was formed by annealing at 950 °C between Ni/Al/Ni/Au and p-type SiC with a doping concentration of 1018cm−3. The aging sensor was tested for varistors in the air of 25 °C–600 °C. The resistance value of the varistors initially decreased and then increased with the increase of temperature and reached the minimum at ~450 °C. It could be calculated that the varistors at ~100 °C exhibited the maximum temperature coefficient of resistance (TCR) of ~−0.35%/°C. The above results indicated that the sensor had a stable electrical connection in the air environment of ≤600 °C. Finally, the encapsulated sensor was subjected to pressure/depressure tests at room temperature. The test results revealed that the sensor output sensitivity was approximately 1.09 mV/V/bar, which is better than other SiC pressure sensors. This study has a great significance for the test of mechanical parameters under the extreme environment of 600 °C.

Critical positive temperature coefficient of resistivity of Li/Y co-doped ZnO ceramics modified by Cr-ions

ZnO-based ceramics doped with Li/Y and modified by various contents of Cr-ions, (Zn0.9475Y0.0025Li0.05)1-xCrxO (0 ≤ x ≤ 0.025), were prepared by a wet chemical route followed by a traditional ceramic sintering technology. The effect of Cr-ion content on the electronic conductivity and resistance–temperature characteristics of the prepared ceramics was investigated. All the ceramics have hexagonal wurtzite ZnO structure, and exhibit critical positive temperature coefficient of resistivity (C-PTCR) effect. With various contents of Cr-ions, the maximum temperature coefficient of resistivity (TCR) reaches 61.1%·°C−1 or the resistivity jump log(ρmax/ρmin) is up to 4.74. The critical transition temperature of resistivity can be adjusted in the temperature range of 76–147 °C for different various contents of Cr-ions. The complex impedance analysis shows that the C-PTCR effect of the ZnO ceramics resulted from both grain effect and grain boundary effect. According to the analysis of the dielectric temperature spectra, the ZnO-based ceramics have ferroelectricity at room temperature, and the ferroelectric–paraelectric transition around the critical transition temperature of resistivity during the temperature increases.

A theoretical calculation for carrier concentration and resistance prediction

Due to lack of analytical solutions for equation of electrical neutrality under thermal equilibrium conditions, a novel and efficient numerical iteration technique was developed. The computational carrier concentration obtained by this new numerical method is in good correlation to commonly cited values and experimental data. Based on this new numerical method effects of some factors on the resistance of silicon piezoresistive pressure sensor were analyzed. Results show that no matter doping concentration is high or low the minority carrier exclusion effect disappears under considerably high current conditions, and increases in bias current induce greater maximum operating temperature; increases in doping concentration can increase the maximum operating temperature and decrease temperature coefficient of resistance.