Papers by Keyword: NTC Thermistor

Abstract: Manganese-based solid solution ceramics of transition metal with spinel-type crystal structure have generated much interest as NTC thermistors in various domestic and industrial applications. Doping has been considered as one of the most important method to improve their electrical properties. In this work, Cr doped Mn-based solid solution NTC ceramics Ni_0.7Mn_2-xCu_0.3Cr_xO₄ (x = 0.1, 0.2, 0.3 and 0.4) were prepared by solid-state reaction method. X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS) were applied to study the phase structure, surface morphology and surface element content. The results indicate that the resistance and B value increase as the substituted Cr content increases.

Abstract: A study on the effect of heat treatment condition on the characteristics of MnO₂ added-Fe₂TiO₅ ceramics for NTC thermistor has been carried out. The ceramics were produced by pressing an homogenous mixture of Fe₂O₃ (local/ yarosite), TiO₂ and MnO₂ (2.0 mole %) powders in appropriate proportions to produce Fe₂TiO₅ based ceramics and sintering the pressed powder at 1050 °C for 3 hours in oxygen gas. Some sintered pellets were heat treated by heating them at 300 °C for 5, 15 and 25 minutes in Ar + 7% H₂ gas. The XRD analyses showed that the Fe₂TiO₅ ceramics with and without heat treatment time had orthorhombic structure. No peak from second phase was observed from the XRD profiles. From the electrical characteristics data, it was known that the heat treatment could change the electrical characteristics of the Fe₂TiO₅ based-thermistor. The thermistor constant (B) and room temperature resistivity (ρ_RT) decreased with the increasing of heat treatment time. All ceramics made had thermistor characteristics namely B = 3459-7596 K and ρ_RT = 1.056-6936.062 MΩcm. Thermistor constant of the ceramics was relatively big, indicated that ceramics made from local iron oxide in this work fit the market requirement for NTC thermistor.

Abstract: Fabrication of Fe₂TiO₅ pellet/disk ceramics-based NTC thermistor has been performed, in order to know the effect of sintering tempertures on the electrical characteristic of 1.0 mole % MnO₂ doped-Fe₂TiO₅ ceramics. These ceramics were made by mixing commercial powders of Fe₂O₃, TiO₂ and MnO₂ with proportional composition to produce Fe₂TiO₅ based ceramic. The raw pellet was sintered at 1100 °C, 1200 °C and 1300 °C temperature for 2 hours in air. Analysis of the microstructure and crystal structure were performed by using a scanning electron microscope (SEM) and x-ray diffraction (XRD) respectively. XRD pattern showed that all of Fe₂TiO₅ ceramics made ​​at various sintering temperatures are orthorhombic The SEM images showed that the grain size of pellet ceramics increase with increasing sintering temperatures. From electrical data that was measured at temperature 30-300 °C, showed that the addition of sintering temperature decreased the thermistor constant (B), activation energy (E_a), thermistor sensitivity (α) and room temperature resistance (R_RT). Thermistor constant (B) of the ceramics was relatively big of 5778 K to 6707 K. The value of B indicated that ceramics made in this work fit the market requirement for NTC thermistor.

Abstract: In the micro-climate cloth researching, we usually need to accurate measuring the body temperature, in this paper we choose the constant-voltage temperature measuring system based on the NTC thermistor to measure the temperature. Because the resistance of the thermistor and the temperature is not linear, so this will cause the output of the measurement circuit is not linear. In actual measurement we usually require the output of the circuit varies linearly in the required range. This paper mainly research the linearization problem of the NTC thermistor bridge circuit in the required temperature range.

Abstract: Mn-Co-Ni-O (Mn:Co:Ni=1.74:0.72:0.54, MCN) thin films with single cubic spinel structure were prepared on Si substrates by metal organic solution deposition (MOSD) method at different annealing temperatures. The effects of annealing temperature on the phase component, crystalline microstructure, surface morphology and electrical properties of the MCN thin films were studied. According to the results of x-ray diffraction pattern, the MCN thin film annealed at 650 had spinel structure. Observation with field emission scanning electron microscope (FE-SEM) on the MCN thin films showed that the grain size increased with increasing annealing temperature. The resistance measured at room-temperature was 18.143, 12.457, 2.435 and 3.141MΩ for the MCN thin films annealed at 650, 700, 750 and 800, respectively. The values of thermistor constant (B_30/85) and activation energy (Ea) were in the range of 3260-4840K and 0.28-0.42eV, respectively.

Abstract: We investigated the electrical properties of the perovskite R(Cr,Mn)O₃ (where R is selected from various rare earth elements and Y), which is suitable for use in negative temperature coefficient (NTC) thermistors. The substitutions of Mn for Cr in La(Cr,Mn)O₃ and larger ions for R³⁺ decreased both the resistivities (r) and thermistor constants (B values) estimated from measurements at 25°C and 50°C according to r = r₀exp(B/T). The activation energies of the carrier number (E_g) and carrier mobility (W_H) were estimated by measuring the thermoelectric power and resistivity. A change in W_H corresponded to a change in the B value. We discussed the relationship between the grand state electronic configuration of the M³⁺ ions and the local lattice distortion around the M³⁺ ions. The change in W_H could be qualitatively linked to the M3d– O2p transfer energy, which is corresponding to the hybridization between the M3d and O2p orbital (M: transition metal elements, O: oxygen).

Abstract: The aim of this paper is to investigate the effects of V2O5 additive on the electrical properties of NTC thermistors based on Ni0.5Co0.5Mn2O4.The XRD analyses indicate that single spinel phase can form, and V2+ions are in the octahedral interspace. The cell can be enlarged due to the V2O5 additive. The resistivities (ρ) and the material constant (B) increase obviously, the reasons of which are mainly attributed to the outer electron configuration of V2+ and cell enlargement.