Thermistor Constant Research Articles

Structural, dielectric, electric, transport, and optical properties of a double perovskite: BaKFeMoO6

In this communication, synthesis (solid-state reaction) and characterization (XRD, SEM, EDAX, RAMAN, UV & LCR) of a double perovskite BaKFeMoO6 (BKFMO) are reported. Monoclinic crystal symmetry with average crystallite size and lattice strain are evaluated as 55 nm and 0.00254 respectively from XRD data. A scanning electron microscope (SEM) study reveals the uniform distribution of grains through well-defined grain boundaries and also discusses their role in the conduction mechanism. Purity and compositional analysis confirm the presence of all constituent elements in both weight and atomic percentage from energy dispersive x-ray analysis (EDAX). The incorporation of the K+ and Fe3+ in the Ba- and Mo-site in the host BaMoO4 is confirmed by Raman's study. Ultraviolet-visible (UV) data calibrate an energy bandgap of 2.9 eV; which may be suitable for photovoltaic applications. The measurement and analysis of dielectric, ac conductivity, and impedance are carried out in a wide range of frequencies (1 kHz- 1 MHz) and temperatures (25°C – 500°C). Maxwell-Wagner type of dielectric dispersion, negative temperature coefficient of resistance (NTCR), thermally activated conduction, and non-Debye type of relaxation are the output of the analysis. The ZSIMPWIN fitted Nyquist's data reveals the grain and grain boundary effect in the conduction mechanism. The analysis of temperature-dependent resistance evaluates thermistor constant (β), sensitivity factor, stability factor, and activation energy; which can be tailored for thermistor-related applications. The study of the polarization–electric field (P-E) loop opens up the possibility of the ferroelectric property in the studied material.

Structural, dielectric, electrical and optical properties of a double perovskite: BaNaFeWO6 for some device applications

In this paper, the synthesis (by solid-state reaction route) and characterization (structural, microstructural, electrical, and optical properties) of the BaNaFeWO6 lead-free double perovskite are reported. Room temperature structural analysis suggests that the material crystallizes in monoclinic crystal symmetry with average crystallite size and lattice strain of 55 nm and 0.023% respectively. The incorporation of the Na/Fe at both sites (Ba and W) of BaWO4 is confirmed from the room temperature Raman study. A study of microstructural and compositional characteristics of the sample by using scanning electron microscopy (SEM) and EDAX (energy dispersive analysis X-ray) has provided the quality (uniform and compactness) of the sample. The detailed studies of the frequency and temperature dependence of dielectric, impedance, and conductivity properties of the material suggest the presence of high dielectric dispersion, non-Debye conduction, and relaxation mechanism in it. The semiconducting nature is confirmed by the decreasing resistance or radius of semicircular arcs in both impedance analysis and Nyquist plots. This nature is also well supported by fitted parameters evaluated using ZSIMPWIN software. The temperature dependence of resistance provides a good stability factor, sensitivity factor, and thermistor constant, which may be useful for applications in the fields of the thermistor-related devices. The field-dependent polarization (P-E) hysteresis loop suggests the possibility of ferroelectricity in the sample. The sample has an energy bandgap of 2.72 eV deduced from its UV–visible spectrum, which may be useful for some applications in optoelectronic devices

Structural, dielectric, electrical and optical properties of Li/Fe modified barium tungstate double perovskite for electronic devices

In this communication, the synthesis (solid-state reaction route) and characterization (structural and electrical properties) of Li/Fe modified barium tungstate BaWO4 of chemical formula (BaLi)(FeW)O6 double perovskite have been reported. Analysis of room temperature X-ray diffraction data shows the formation of a new single-phase (double perovskite) of tetragonal symmetry. The calculated average crystallite size and lattice strains are found to be 42 nm and 0.111% respectively. The scanning electron micrograph shows that grains are distributed uniformly with less porosity in the material. Detailed studies of field (frequency) and thermal (temperature) dependence of capacitive (dielectric) and resistive (impedance and conductivity) characteristics of the prepared material have shown the dielectric dispersion, relaxation, and non-Debye type of conduction mechanism respectively of the material. The existence of a non-Debye type of relaxation process and thermally activated relaxation process in the material has been analyzed by using impedance spectroscopy and conductivity techniques respectively. The presence of the depressed semicircular arcs in both Nyquist and Cole-Cole plots confirms the semiconductor nature of the material, which is well supported from ZSIMPWIN fitted impedance data. Study of room temperature Raman spectra supports the incorporation of Li/Fe of LiFeO2 in BaWO4 to produce new double perovskite of a composition BaLiFeWO6 of tetragonal symmetry. Further, as the temperature dependence of resistance shows a good stability factor, sensitivity factor, and thermistor constant, the material may be useful for thermistor-related devices. The nature of I–V characteristics confirms the presence of the Ohmic type of conductivity of the material. The energy bandgap of 2.85 eV, obtained from the UV–visible spectrum, suggests the material may also be used for optoelectronic devices.

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.

Studies on structural, dielectric and optical properties of Cu/W double substituted calcium manganite for solar cells and thermistor applications

ABSTRACT In this communication, the synthesis of modified calcium manganate (CaCu1/3Mn1/3W1/3O3) ceramics by a conventional solid-state reaction technique is reported. The possibility of the incorporation of Cu/W ions in the B-site of the CaMnO3 ceramics is investigated. The structural analysis predicts a rhombohedral structure with space group R-3c (#167). The average crystallite size and lattice micro-strain are about 35.6 nm and 0.776%. The Raman study confirms the presence of all constituent while UV-Vis provides energy bandgap 4.69 eV; suitable for solar cell. The study of complex impedance suggests Cole–Cole type relaxation and bulk resistance decreases from 1.407 × 107 Ω at 25°C to 2.201 × 103 Ω at 500°C, which confirms the negative temperature coefficient of resistance (NTCR) character. The semi-circular arcs in the Cole–Cole and Nyquist plots confirm the semiconductor nature. Thermistor constant (β), sensitivity factor (α) and stability factor of the sample were calculated which confirm the characteristics of NTC thermistor.

Effect on Structural, Electrical and Temperature Sensing behavior of Neodymium Doped Bismuth Ferrite

Synthesis of polycrystalline samples of Bi1-xNdxFeO3 [x = 0.5, 0.6, 0.7 and 0.8] were demonstrated following solid-state reaction method at high temperature. The structural properties of the sample were confirmed through the X-ray diffraction technique. The dielectric study of the compounds was performed at different frequencies in the range of 100 Hz – 10 6 Hz for various temperatures. The non-Debye type of relaxation process confirmed from impedance analysis. The materials showed a negative temperature coefficient of resistance (NTCR) behavior at various temperatures and frequencies. AC conductivity of the materials with frequency at different temperatures satisfied the universal power law of Johnscher. Thermistor constant (β), sensitivity factor (α), and stability factor for all the samples were calculated and confirmed the characteristics of NTC thermistor.

Cofiring of LTCC multilayer assemblies with integrated NTC thermistor temperature sensor layers

We have studied the integration of Ni–Co–Zn–Mn spinel NTC thermistor layers into LTCC multilayer modules. Sintering of the cubic spinel Ni0.5Co0.5Zn0.75Mn1.25O4 with addition of 3 wt% Bi2O3 additive at 900 °C resulted in samples with 96% density and with good electrical performance. Thermistor spinel tapes, fabricated using doctor blade tape casting, were stacked with layers of a commercially available low-k dielectric LTCC tape, and cofired at 900 °C. Free or constrained cofiring did not give crack-free multilayer samples. Thermistor layers were then integrated combining the commercial LTCC tape with a Zn titanate-based tape in one multilayer laminate, and error-free multilayer samples with a room-temperature resistivity of ρ298 = (2,9 ± 0.08) kΩcm and a thermistor constant of B = (4280 ± 200) K were obtained. This demonstrates the possibility of cofiring of functional ceramic and low-k LTCC tapes and shows the potential of NTC spinel thermistor layers as temperature sensors integrated in complex LTCC multilayer architectures.

Solution Synthesis of Cubic Spinel Mn-Ni-Cu-O Thermistor Powder.

Toward the development of NTCR thermistors, nanocrystalline Mn–Ni–Cu–O powder was synthesized from a mixed chloride aqueous solution by a simple co-precipitation method.The introduction of an oxidizing agent (H2O2) into the solution led to the partial oxidation of Mn2+ ions into Mn3+ ions, which enabled the collected powder to be well crystallized at 650 °C. Such a low calcining temperature resulted in fine particles with a mean size of 60 nm, which significantly promoted densification of the resulting ceramics. As a result, a dense and homogenous microstructure with a relative density up to 97.2% was achieved for pellets sintered at 1100 °C. Furthermore, these sintered ceramics exhibited a room temperature resistivity (ρ25) of 67 Ω·cmand a thermistor constant (B25/85) of 2843 K, which make them suitable for use in industrial thermistors. In addition, electrical stability was greatly improved when the ceramics were prepared by a new two-step sintering method. The results suggest that the co-precipitation route with the introduction of H2O2 is suitable for the fabrication of cubic spinel thermistor nanopowders.

Effect of phase structures and substrate temperatures on NTC characteristics of Cu-modified Ba–Bi–O-based perovskite-type thermistor thin films

Based on the formula of BaBi0·92Cu0·08O3, Cu-modified Ba–Bi–O-based perovskite-like negative temperature coefficient (NTC) thermistor thin films were successfully prepared by radio frequency (RF) magnetron sputtering method with the various deposition temperatures (25 °C, 100 °C, 200 °C and 250 °C). The effects of the substrate temperatures on the phase structures and electrical properties were respectively characterized and investigated by X-ray diffraction (XRD), resistance-temperature measurement, and complex impedance analysis for the Ba–Bi–O-based thin films. Additionally, the cross-sectional microstructures and grain morphologies of the BaBi0·92Cu0·08O3 thin films were analyzed by scanning electron microscope (SEM) and atomic force microscope (AFM). The XRD patterns results showed that the perovskite monoclinic structure with a small amount of BaBiO2.5 s phase could be obtained for the BaBiO3 thin film deposited at 200 °C, and also, the main crystalline phase was transferred from BaBiO2.82 to BaBiO2.5 when the BaBi0·92Cu0·08O3 thin films were deposited at 200 °C and 250 °C, respectively. Temperature dependent complex impedance spectroscopy was carried out to make clear the resistance contribution of grain (Rg), grain boundary (Rgb) and contact (Rs) response for the conduction mechanisms in the Ba–Bi–O-based thin film deposited at a given substrate temperature. Compared with the electrical properties of the BaBiO3 thin film deposited at 200 °C [such as the room-temperature resistivity (ρ25 ~ 1548 Ω cm) and the thermistor constant (B25/85–3245 K)], the better NTC characteristics of a lower ρ25 value of about 956 Ω cm and a higher B value of approximately 3480 K were found in the BaBi0·92Cu0·08O3 thin film deposited at a same temperature (200 °C). It is believed that the phase structures and electrical properties of the BaBiO3 perovskite-type NTC thermistor thin films could be adjusted and optimized by a trace amounts of Cu-ions substitutions and depositing at an appropriate substrate temperature, which also showed that such as these novel BaBiO3-based thin films are feasible with the extensive of actual applications for the NTC thermistors.

Ultrathin Highly Flexible Featherweight Ceramic Temperature Sensor Arrays.

We fabricated highly flexible Sr- and Ni-doped perovskite SmMnO3 thermistor film sensor arrays on an ultrathin (5 μm thick) and lightweight (21 mg) polyimide sheet for healthcare monitoring devices. The Ag nanowire and nanoparticle-impregnated carbon microcone array, which was prepared by precisely controlled surface laser carbonization of polyimide, showed sufficiently low resistance as a bottom electrode and good stability against sharp bending angles. The dot-shaped (diameter: 900 μm) perovskite thermistor film with a thickness of 900 nm was crystallized by pulsed ultraviolet laser irradiation of a precursor film printed with perovskite nanoparticle dispersion ink, and the film functioned well as the thermistor with a thermistor constant of 2820 K. The thermistor sensor sheet exhibited rapid responses to temperature variation and high stability in the temperature cycle tests over 1000 cycles between room temperature and 80 °C. The bending durability for a bending angle of 60° with a small bending radius (500 μm) was also high. During the bending test over 1000 cycles, the monitoring temperature variation was suppressed only within 0.1 °C. This ultrathin sensor array sheet can be mounted on surfaces with shape variations, and we used the sensor for real-time monitoring in healthcare to detect precise temperature variations on the human skin during physical exercise.

Structure and electrical properties of Bi0.5Ba0.5FeO3-Y2O3 composite NTC ceramics

(1 − x) Bi0.5Ba0.5FeO3 (BBF)-xY2O3 negative temperature coefficient (NTC) ceramics were prepared by solid-state reaction method. With increasing Y2O3 contents, the grain sizes of the samples increase. All (1 − x) BBF-xY2O3 ceramics have the typical NTC effect. The conductive mechanism of BBF based ceramics is largely the electron hopping. The thermistor constants B25/75 of the (1 − x) BBF-xY2O3 ceramics keep the lager values in the range of 6441 to 7611 K. The resistivity at 25 °C decreases from 7.82 × 107 Ω cm for the pure BBF ceramic to 106 Ω cm magnitudes for the 0.80 BBF-0.20Y2O3 ceramic. The activation energy Ea of samples is in the range of 0.5003–0.5529 eV. The impedance analysis indicates that the grain boundary resistances are higher than intragrain resistances in BBF based ceramics. All samples have the single relaxation process, and the relaxation phenomena are attributed to hopping of oxygen vacancies.

Gamma radiation induced fabrication of styrene butadiene rubber/ magnetite nanocomposites for positive temperature coefficient thermistors application

A new positive temperature coefficient resistor (PTCR) thermistor based on styrene butadiene rubber/nanomagnetite (SBR/Fe3O4) nanocomposite was successfully fabricated by conventional roll milling technique.XRD, FT-IR,TEM and EDX techniques were utilized to elucidate the developed of magnetite nanoparticles the analyses revealed a diameter of 9–11 nm.The (SBR/Fe3O4) nanocomposite was examined via the XRD patterns and SEM micro images before and after gamma irradiation. The mechanical properties of the developed nanocomposites: tensile strength, elongation at break and elastic modulus were investigated, whilst the thermal stability was analyzed by TGA. Explicit improvement was been noticed by elevation of the nano load and radiation dose within the cited range. The electrical conductivity examination and the derived thermistor constant, sensitivity and stability of irradiated nanocomposite, 10% Fe3O4 at 100 kGy ensured typical PTCR.

The Effect of Various Sintering Condition to the Electrical Characteristics of Fe2TiO5Ceramics for NTC Thermistor

Iron Titanium Oxide (Fe2TiO5) ceramics for negative temperature coefficient (NTC) thermistor have been synthesized in various sintering condition in order to know the effect of sintering condition, namely, temperature, time and atmosphere condition, on the characteristic especially the electrical characteristic of Fe2TiO5 ceramics. Temperature conditions are adjusted between 1200 and 1300°C, for 2 and 8 hours in furnace with atmospheric air and oxygen (O2) gas. For Fe2TiO5 ceramics sintered in the air, the effect of sintering temperature on the grain size was clearly seen. With increasing sintering temperature and sintering time, grain size of Fe2TiO5 ceramics increased. However, the effect of atmospheric O2 gas to their grain size is not clearly seen although it has reduced tendency. XRD analysis showed that all ceramics Fe2TiO5 are single phase of orthorhombic structure. From electrical resistances data that was measured at temperature 40 - 250°C, it is found that the value of thermistor constant (B), activation energy (Ea) and room temperature resistance (RRT) decreases with increasing sintering temperature and sintering time. But the value of B, Ea, and RRT increases with atmospheric O2 gas condition.

Sintering Temperatures Investigation on the Electrical Characteristics of Fe<sub>2</sub>TiO<sub>5</sub>/MnO<sub>2</sub> Ceramics-Based NTC Thermistor

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 (Ea), thermistor sensitivity (α) and room temperature resistance (RRT). 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.

Effect of Heat Treatment Condition on the Characteristics of MnO<sub>2</sub> Added-Fe<sub>2</sub>TiO<sub>5 </sub>Ceramics for NTC Thermistors Using Local Iron Oxide

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 (ρRT) decreased with the increasing of heat treatment time. All ceramics made had thermistor characteristics namely B = 3459-7596 K and ρRT = 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.

Highly stable flexible thermistor properties of spinel Mn-Co-Ni oxide films on silver/carbon micro-pinecone array composite electrodes

We fabricated flexible Mn1.56Co0.96Ni0.48O4 (MCN) thermistors with stable electrical properties by precisely optimizing precursors and electrodes. The composite Ag and carbon micro-pinecone (CMP) arrays were fabricated with a KrF laser directly from polyimide sheets containing silica nanoparticles and functioned well as electrodes with high bending resistance. The electrical resistance was stable even after 10 000 bending test cycles. The well-crystallized MCN film thermistors were fabricated on the Ag/CMP composite electrodes by KrF laser irradiation at 55 mJ·cm−2 for 600 pulses to optimize the precursor films consisting of MCN nanoparticles and amorphous Mn-Co-Ni oxides. The MCN film thermistors showed high thermistor constants at 3633 K, low electrical resistivity at 10.7 kΩ·cm at 37 °C, and remarkably good stability during 10 000 bending cycles (the change in resistance was only 0.6%). The MCN film thermistors also had excellent temperature cycle resistance at 20–150 °C (3000 cycles). Thus, we improved the reliability of flexible thermistors for application in various kinds of wearable devices.

The Effect of MnO2 Content and Sintering Atmosphere on The Electrical Properties of Iron Titanium Oxide NTC Thermistors using Yarosite

The effect of MnO2 content and sintering atmosphere on the characteristics of Fe2TiO5 ceramics for Negative Thermal Coefficient (NTC) thermistors by using Fe2O3 derived from yarosite has been studied. The ceramics were produced by pressing a homogeneous mixture of Fe2O3, TiO2 and MnO2 (0-2.0 w/o) powders in appropriate proportions to produce Fe2TiO5 based ceramics and sintering the pressed powder at 1100-1200°C for 3 hours in air, O2 and N2 gas. Electrical characterization was done by measuring electrical resistivity of the sintered ceramics at various temperatures from 30°C to 200°C. Microstructure and structural analyses were also carried out by using an scanning electron microscope (SEM) and x-ray diffraction (XRD). The XRD data showed that the pellets crystallize in orthorhombic. The presence of second phase could not be identified from the XRD analyses. The SEM images showed that the grain size of pellet ceramics increase with increasing of MnO2 addition, and the grains size of the ceramic sintered in oxygen gas is smaller than sintered in nitrogen gas. Electrical data showed that the value of room temperature resistance (RRT) tend to decrease with respect to the increasing of MnO2 addition and the pellet ceramics sintered in oxygen gas had the largest thermistor constant (B), activation energy (Ea), sensitivity (α) and room temperature resistance (RRT), compared to the sintered in nitrogen gas. From the electrical characteristics data, it was known that the electrical characteristics of the Fe2TiO5 pellet ceramics followed the NTC characteristic. The fabricated Fe2TiO5 ceramics have thermistor constants (B = 2207-7145K). This can be applied as temperature sensor, and will fulfill the market requirement.

The Effect of Sintering Atmosphere on Electrical Characteristics of Fe2TiO5 Pellet Ceramics Sintered at 1200°C for NTC Thermistor

Fabrication of Fe2TiO5 pellet ceramics using powder metallurgy technique for NTC thermistor has been carried out, in order to know the effect of sintering atmosphere (Oxygen, Air and Argon Gas) on the characteristic especially the electrical characteristic of Fe2TiO5 ceramics with high working temperature. X-ray diffraction analyses (XRD) was done to know crystal structure and phases formation. A SEM analysis was carried out to know microstructure of pellets. Electrical properties characterization was done through measurement of electrical resistance at various temperatures (room temperature to 250oC). The XRD data showed that the pellets crystallize in orthorhombic. The presence of second phase could not be identified from the XRD analyses. The SEM images showed that the grains size of the ceramic sintered in oxygen gas is smaller than that of the ceramic sintered in air and argon gas. Electrical data showed that the pellet ceramics sintered in oxygen gas had the largest room temperature resistance (RRT), thermistor constant (B), activation energy (Ea) and sensitivity (α) compared to those sintered in air and argon gas. From the electrical characteristics data, it was known that the electrical characteristics of the Fe2TiO5 pellet ceramics followed the NTC characteristic. The value of B and RRT of the produced Fe2TiO5 ceramics namely B = 4389-6149 K and Rrt = 342-26548kQ, fitted market requirement and can be used for temperature sensor.

Effect of Ba0.5Bi0.5Fe0.9Sn0.1O3 addition on electrical properties of thick-film thermistors

Thick-film thermistor with negative temperature coefficient (NTC), low room-temperature resistivity and modest thermistor constant was screen-printed on the alumina substrate by the combination of with Ba0.5Bi0.5Fe0.9Sn0.1O3. The electrical properties of the thick films were characterized by a digital multimeter, a Keithley 2400 and an impedance analyzer. The results show that with the Ba0.5Bi0.5Fe0.9Sn0.1O3 content increasing from 0.05 to 0.25, the values of room-temperature resistivity, thermistor constant and peak voltage of the thick films increases and are in the ranges of 1.47-26.5 O-cm, 678-1345 K and 18.9-47.0 V, respectively. The corresponding current at the peak voltage of the thick films decreases and is in the range of 40-240 mA. The impedance spectroscopy measurement demonstrates that the as-prepared thick films show the abnormal electrical heterogeneous microstructure, consisting of high-resistive grains and less resistive grain boundary regions. It can be concluded that the addition of Ba0.5Bi0.5Fe0.9Sn0.1O3 into improves the thermistor behavior and but also deteriorates the current characteristics.

Effect of Nb<sub>2</sub>O<sub>5</sub> Addition to the Electrical Properties of Fe<sub>2</sub>TiO<sub>5 </sub>Ceramics-Based NTC Thermistor

The aims of this research is to identify the effect of Nb2O5addition on the electrical properties of Fe2TiO5ceramics-based NTC thermistor.The concentration of Fe2O3and TiO2was proportional to Fe2TiO5, whereas the concentration value of Nb2O5were 0, 0.5 and 1.0 mole %, respectively. Within two hours, the mixed powder was pressed at 4 ton/cm2to form pellets and sintered at 1300 °C in air. It can perceived from the XRD data that the sintered ceramics had single phase of Fe2TiO5, pseudobrookite. From SEM data, it is found that addition of Nb2O5decreases the grain size. The addition of Nb2O5increases thermistor constant, activation energy and electrical resistance of Fe2TiO5ceramics. The values of thermistor constant of Nb2O5added-Fe2TiO5ceramics were relatively large, indicated that the ceramics were aplicable as the NTC thermistor.