Temperature Coefficient Of Resistance Effect Research Articles

Thickness-Dependent Electrical Characteristics of Sputtered BFO Thin Films over Wide Temperature Range

This study explores how thickness and grain size impact leakage current in RF-sputtered BFO thin films. Morphology reveals that increasing film thickness leads to larger grains, boosting grain resistivity by altering oxygen vacancies, thus reducing leakage current. Pt/Ti/BFO/FTO capacitive heterostructures are examined at varied temperatures, demonstrating a positive temperature coefficient of resistance effect. This effect stems from the closely linked interaction between multiferroic BFO and highly conductive oxide FTO, and potentially forming an electrical double layer at the Pt/Ti/BFO interface. Additionally, a dominant modified Space Charge Limited Current conduction mechanism is observed in Pt/Ti/BFO/FTO capacitive heterostructures under varying electric fields.

X-ray photoelectron spectroscopy and temperature-dependent electrical transport properties of MnFe2O4-reduced graphene oxide nanocomposites

The reduced graphene oxide (rGO) sheets are assembled with MnFe2O4 (MFO) nanoparticles via an in-situ sol–gel autocombustion route to obtain MFO@rGO nanocomposites. The investigation of their structural and electrical properties is carried out through X-ray photoelectron spectroscopy (XPS) and impedance analyzer, respectively. XPS study discloses the presence of C, O, Fe, and Mn in the MFO@rGO composite, indicating the decoration of MnFe2O4 nanoparticles by rGO sheets. XPS study also reflects the mixed Fe3+/Fe2+ oxidation states of Fe and mixed Mn2+/Mn3+oxidation states of Mn in the composite. The highest value of ac conductivity (σac = 7.51 × 10−6 Ω−1 cm−1 at 1 MHz) at room temperature is obtained within the vicinity of the percolation threshold when rGO content is 20 wt%. The ac conductivity of composites increases with frequency up to 100 °C and then becomes independent of the frequency with a further increase in temperature. The impedance gradually decreases with temperature, revealing the occurrence of negative temperature coefficient of resistance effect in composites. The findings suggest that the MFO@rGO composites can be a potential nominee for the fabrication of electrodes for supercapacitors and flexible electronic devices of low resistance and high electrical conductivity for high-frequency applications.

Dielectric properties of alumino-silicate ceramics synthesized by plasma sintering

The polycrystalline ceramic specimens of three different alumino-silicate solid solutions (Al0.70Si0.30O, Al0.73Si0.27O and Al0.75Si0.25O) consisting of different alumina and silica concentrations have been synthesized by thermal plasma sintering technique. From structural analysis carried out by X-ray diffraction, the ceramics are mostly found to consist of two different phases of mullite and sillimanite. SEM images of these ceramics reveal a high dense and less porous microstructure with homogeneous distribution of grains throughout their surface. These materials exhibit high dielectric constant value (>103) with low dissipation factor. The AC conductivity analysis reveals that Al0.70Si0.30O and Al0.75Si0.25O ceramics possess room temperature conductivity values of the order of 10−5, whereas Al0.73Si0.27O has conductivity of 10−7 order that increases with rise in temperature. From the Nyquist plots, the grain and grain boundary conductivities are distinguished and negative temperature coefficient of resistance behavior is identified in these ceramics with small positive temperature coefficient of resistance effect.

Barium titanate-based thermistors: Past achievements, state of the art, and future perspectives

Barium titanate materials displaying a positive temperature coefficient of resistivity are ubiquitously employed as thermistors in electrical current and voltage control systems, as well as in gas and thermal sensing applications. The positive temperature coefficient of resistivity effect is widely accepted to be a grain boundary-based phenomenon, although detailed studies on grain boundary structure and chemistry, and their influence on the resulting electrical properties, are seriously lacking. Tailoring of the positive temperature coefficient of resistivity electrical characteristics, for specific high-value applications, will require improved understanding and control over grain boundary phenomenon. A comprehensive overview of the development of barium titanate-based positive temperature coefficient of resistivity ceramics is initially presented. We then advance to a discussion on emerging grain boundary characterization techniques, specifically, a stereographic analysis of electron backscatter diffraction data that could assist in enhancing control over BaTiO3 defect chemistry and microstructure, through characterization and subsequent manipulation of the population of grain boundary types. These techniques have great potential for increasing the understanding of the delicate interplay between processing conditions, chemistry, microstructure, and functional electrical properties, and are relevant to the development of advanced, high-performance ceramics and electroceramics in general. Contemporary advancements in the field, such as lead-free positive temperature coefficient of resistivity effect materials and multilayer miniaturized systems based on hypostoichiometric barium compositions, are reviewed. Finally, perspectives on future lines of thermistor research, with a focus on the energy sector, are presented including applications in gas separation and chemical sensing.

Colossal and anomalous dielectric behavior in grain-oriented TiO2

In this work, anatase structure TiO2 particles with a preferential grain growth direction of [002] were synthesized by a facile and modified sol–gel approach. The pellets pressed from the TiO2 particles possess colossal dielectric constant (> 7 × 103 at 100 Hz and room temperature). The colossal dielectric constant behavior can be associated with the Maxwell–Wagner relaxation due to the textured grain structure. This approach is simple and provides an avenue to obtain the excellent dielectric properties of ceramics with oriented grains. Contrary to traditional relaxation behavior, an anomalous dielectric behavior was observed above room temperature. This abnormal dielectric behavior was caused by the positive temperature coefficient of resistance effect resulting from humidity response.

Effect of Laser Irradiation on the PTCR Behavior of Semiconducting Barium Strontium Titanate Ceramics

This paper examines the effect of pulsed laser irradiation on the electrical properties of n-type semiconductor ferroelectric ceramics (based on a (Ba,Sr)TiO3 solid solution) with a planar contact configuration. The elemental compositions and surface morphologies of the material before and after laser irradiation are compared using scanning electron microscopy data. In the framework of the well-known Heywang model for the positive temperature coefficient of resistance effect, we calculate the resistance of the material as a function of temperature for the paraelectric phase and determine parameters of grain boundaries that ensure good agreement between the experimental data and theoretical curves.

Abnormal reoxidation effects in Ba‐excess La‐doped BaTiO3 ceramics prepared by the reduction‐reoxidation method

AbstractBa‐excess La‐doped BaTiO3 ceramics have been successfully applied to prepare laminated chip thermistor. Ceramics were firstly fired in a high‐purity N2 flow and then reoxidized in air to obtain positive temperature coefficient of resistivity effect. However, an abnormal reduction trend of room‐temperature (RT) resistivity was found to be always beginning at ~800°C during reoxidation. This anomaly was found closely correlated with the insulating second phase (Ba2TiO4) at grain boundary, which destroyed conducting pathways between semiconducting BaTiO3 grains. When reoxidation temperature was up to ~800°C, the insulating Ba2TiO4 could be gradually consumed and then conducting pathways reestablished leading to RT resistivity reduction. To further prove the proposed explanation, the reoxidation effects of TiO2‐added ceramics were also studied, in which no Ba2TiO4 existed and certainly the abnormal RT resistivity reduction disappeared.

Improvement of the dielectric and ferroelectric properties of multiferroic Pb(Fe1/2Nb1/2)O3 ceramics processed in oxygen atmosphere

Multifunctional materials such as the multiferroic compound Pb(Fe1/2Nb1/2)O3, are of great interest from the academic and technological points of view. However, the occurrence of Fe2+ and oxygen vacancies originated during the sintering process increase the dielectric loss and electrical conductivity, detrimental to optimal device performance. Here, a report on the effects of a saturated O2 atmosphere used during the calcination and sintering stages is presented. A comparative study of structural, morphological, and physical properties with those obtained for samples sintered in air or in its own atmosphere, is presented. The O2 atmosphere enhances the dielectric constant by ~180 % (with maximum e r of 12700 at T C = 103 °C and dielectric loss smaller than 0.01 independent of frequency and temperature below 100 kHz and T C, respectively), the maximum and remanent polarization by ~275 % (P max from 6.2 to 16.8 µC/cm2 and P r from 2.4 to 6.7 µC/cm2 at 16 kV/cm), and reduces the electrical conductivity by one order of magnitude (from ~1 × 10−7 to ~3 × 10−8/Ω cm at 1 kHz at room temperature). Additionally, a pronounced ac positive temperature coefficient of resistivity effect, strongly dependent on frequency and with potential barrier values from 0.2 eV at 1 kHz to 0.71 eV at 500 kHz, is associated with the highly resistive and capacitive behavior of the grain boundary.

Influence of cooling mode on the electrical properties and microstructure of Ba1.022−xSmxTiO3 ceramics sintered in a reducing atmosphere

We investigated the effects of the Sm-dopant content and the cooling rate on the electrical properties and microstructure of Ba1.022−xSmxTiO3 (BST) ceramics, which were sintered at 1200°C for 30min in a reducing atmosphere and then reoxidized at 800°C for 1h. The results indicated that the cooling rate affected the electrical properties and the microstructure of the BST samples, whose room-temperature resistivity increased with increasing cooling rate. The semiconducting BST ceramics showed a pronounced positive temperature coefficient of resistivity effect, with a resistance jump greater by 3.16 orders of magnitude, along with a low room-temperature resistivity of 157.4Ωcm at a cooling rate of 4°C/min. The room-temperature resistivity of the specimen was lower after sintering for 30min at 1150°C during cooling.

Positive temperature coefficient of resistance effect in Na2Ti6O13-doped 0.94BaTiO3–0.06(Bi0.5Na0.5)TiO3 ceramics

The positive temperature coefficient of resistance (PTCR) characteristics of Na2Ti6O13 (NT)-doped 0.94BaTiO3–0.06(Bi0.5Na0.5)TiO3 (BBNT) ceramics were investigated in order to evaluate the effect of NT as a new additive for lead-free PTCR thermistor application. The BBNT ceramic sintered at 1325°C exhibited a relatively high Curie temperature (TC) of 158°C while its PTCR characteristic was not satisfactory for thermistor application. However, doping with NT significantly influenced the PTCR behavior of BBNT ceramic. It is considered that NT was responsible for grain growth of the BBNT by forming a liquid phase during sintering due to its low melting temperature of 1300°C. The grain growth resulted in the enhanced PTCR characteristics of BBNT ceramic. In particular, 0.1 mol% NT doped BBNT ceramic exhibited excellent PTCR performance of low resistivity at room temperature (1.6×102 Ω cm), resistivity increase near TC (1.28×104) and high TC of 158°C, suitable for lead-free PTCR thermistor application.

Preparation and electrical properties of (1 − x)(Ba,Y)TiO3 · xPbTiO3 materials containing low-melting B2O3-PbO-SiO2 glass additions

We have studied the electrical properties of (1 − x)(Ba,Y)TiO3 · xPbTiO3-based solid solutions containing different percentages of low-melting glass. The materials were prepared by solid-state reactions, sintered in air at temperatures from 1100–1300°C, and characterized by complex impedance measurements in wide frequency and temperature ranges. The results demonstrate that the positive temperature coefficient of resistance effect in these materials, containing different percentages of low-melting glass, is contributed mainly by both the grain boundaries and surface layer. With increasing glass content, the ratio of the maximum resistivity to the minimum resistivity increases and the influence of the surface layer on the positive temperature coefficient of resistance effect becomes stronger. With increasing glass content, the grainboundary potential barrier height in the (1 − x)(Ba,Y)TiO3 · xPbTiO3 materials increases.

Influences of Ba/Ti Ratios on the Positive Temperature Coefficient of Resistivity Effect of Y-Doped BaTiO3-(Bi1/2Na1/2)TiO3 Ceramics

Y-doped (1−x mol%)BaTiO3–x mol%(Bi1/2Na1/2)TiO3 (BBNTx) lead-free positive temperature coefficient of resistivity (PTCR) ceramics were prepared using a conventional solid sintering method. The Ba/Ti ratio was adjusted to obtain the optimized PTCR property. The results show that all 0.2 mol% Y-doped BBNT15 samples with various Ba/Ti ratios have formed a single tetragonal perovskite phase by sintering in an N2 atmosphere. The sample with 5 mol% (Bi1/2Na1/2)TiO3 has only a minor PTCR effect (maximum resistivity [ρmax]/minimum resistivity [ρmin]) when sintered in N2. However, the PTCR effect is enhanced over 3.0 orders of magnitude when the (Bi1/2Na1/2)TiO3 content is >8 mol%. The PTCR characteristics of the samples with Ti excess are superior to those with Ba excess. The optimum composition of 0.2 mol% Y-doped BBNT15 with Ba/Ti=0.99, sintered at 1250°C for 3 h in an N2 atmosphere, has a low room-temperature resistivity (ρ25) of ∼100 Ω·cm and a high PTCR effect of ∼4.8 orders of magnitude with Tc around 190°C.

Effect of γ‐ray irradiation on morphology and electrical properties of poly(vinyl chloride)/graphite composites

AbstractThis article reports the effect of crosslinking by γ‐ray irradiation on the morphology, electrical properties, and hardness of poly(vinyl chloride)/graphite composite. A comparison of the scanning electron micrographs of the composites, before and after irradiation, showed that the filler particles were broken into pieces and distributed homogenously as a result of irradiation. The data of electrical conductivity versus graphite content was found to be consistent with the percolation model. A significant increase in the conductivity of composite was observed on the crosslinking of the polymer in consequence of irradiation. The data are correlated with the morphological changes. The study of electrical resistivity as a function of temperature revealed that the negative temperature coefficient of resistivity effect is considerably suppressed after irradiation. These results are explained on the basis of morphological changes in the composites after γ‐ray irradiation. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

High Tc lead-free BaTiO3–(Bi1∕2Na1∕2)TiO3 positive temperature coefficient of resistivity ceramics with electrically heterogeneous structure

A distinct positive temperature coefficient of resistivity effect has been observed in BaTiO3–(Bi1∕2Na1∕2)TiO3 (BT-BNT) ceramics sintered in a N2 flow with low O2 concentration. With the addition of BNT, the samples exhibit resistivity jumps of ∼103–105 starting at ∼190–210°C. X-ray diffraction results indicate that the BNT phase and BT phase formed a solid solution during sintering. An electrically heterogeneous structure, consisting of the grain interiors, outer grain shells, and grain boundaries, is revealed by the complex impedance analyses. The observed dc resistivity jump is attributed to the rapid resistivity rise in both grain boundaries and grain shells.

Positive Temperature Coefficient of Resistivity Effect of Semiconducting BaTiO3–(Bi1/2Na1/2)TiO3 Ceramics Prepared by a Wet-Chemistry Route

Without any additional donor dopants, BaTiO3–(Bi1/2Na1/2)TiO3 (BT–BNT) positive temperature coefficient of resistivity (PTCR) ceramics were successfully prepared by a wet-chemistry route. With 2 mol % BNT addition, the obtained BT–BNT ceramics had semiconductivity and exhibited a PTCR behavior at about 155 °C. The onset temperature of the PTCR effect increased to ∼165 °C for the 4 mol % BNT added samples. Room-temperature resistivity ρRT increased with the content of BNT added and the ceramics changed from a semiconductor to an insulator, which was consistent with the variation of the microstructure. The temperature of resistivity anomaly in BT–BNT ceramics also increased with increasing BNT content. A small amount of manganese (Mn) dopant was found to improve the PTCR effect in the BT–BNT system. The possible mechanism underlying the PTCR effect in BT–BNT ceramics was proposed.

The effects of the spinodal microstructure on the electrical properties of TiO 2–SnO 2 ceramics

The electrical properties of ceramics within the TiO 2–SnO 2 system which exhibit spinodal decomposition were investigated under different annealing conditions. Changes in the lattice parameter and the phase evolution of the spinodal decomposition, measured in terms of the volume fraction transformed X( t), were examined as a function of annealing time using X-ray diffraction. The room temperature dielectric properties were measured and compared to dielectric mixing rules. Doping with pentavalent Nb was found to slow the decomposition kinetics and a high permittivity ( ε r > 1000 ) was induced. The origin of the high permittivity is linked to the formation of an electrically heterogeneous structure which is derived from the spinodal microstructure. Lastly, it was observed that Nb-doped TiO 2–SnO 2 ceramics exhibited non-linear current–voltage behavior which can be attributed to the negative temperature coefficient of resistance effect.

Positive temperature coefficient resistance and humidity sensing properties of Cd-doped ZnO nanowires

Cd-doped ZnO nanowires in mass production were synthesized by evaporating metal zinc (Zn) and cadmium (Cd) at 900 °C. Devices using the synthesized nanowires were fabricated on microstructured substrates. Cd-doped ZnO nanowires show a clear positive temperature coefficient of resistance effect, which is quite abnormal as compared to pure ZnO nanowires. At room temperature, resistance change of more than three orders of magnitude was measured when Cd-doped ZnO nanowire device was exposed to a moisture pulse of 95% relative humidity.

Positive temperature coefficient of resistivity effect in niobium-doped barium titanate ceramics obtained at low sintering temperature

A positive temperature coefficient of resistivity (PTCR) effect was observed for low temperature sintered Nb-doped BaTiO 3 ceramics using YB 6 as a sintering aid. A semiconducting BaTiO 3 with good PTCR property was obtained at a low sintering temperature of 1150 °C because of the addition of YB 6. Addition of 0.2 mol% Nb 2O 5 and 1 mol% of YB 6 led to a low room-temperature resistivity and a resistivity jump of about 10 4. Room-temperature resistivity of the ceramics was controlled by the grain boundary resistivity which was related to the added amount of YB 6 and the sintering temperature. YB 6 only worked as a sintering aid to enhance the densification of semiconducting BaTiO 3 ceramics at low sintering temperature.

Positive temperature coefficient of resistivity effect in Pb-doped KnbO3

KnbO3 is a ferroelectric material with a Curie temperature (TC) at 415°C, thus giving it the potential to be a material for high-temperature positive temperature coefficient of resistivity (PTCR) applications. In this study, we investigated the PTCR effect in donor-doped KnbO3 ceramics containing 0, 0.1, 0.2, and 0.3 mol% PbO. The donor-doped KnbO3 ceramics exhibited a PTCR anomaly with a relatively low room-temperature resistivity. The temperature of the tetragonal-to-cubic phase transition (TC) of the KnbO3 decreased with the amount of added PbO, while the orthorhombic-to-tetragonal phase transition (TOT) remained unchanged.

Positive Temperature Coefficient of Resistance Effect in Heavily Niobium-Doped Barium Titanate by the Growth of the Double-Twinned Seeds

Positive temperature coefficient of resistivity (PTCR) was attained in heavily niobium-doped BaTiO3 through the addition of BaTiO3 seed particles. The seed particles containing a double twin grew during heat treatment, and a uniform microstructure composed of large, coarse grains was obtained. The incorporation of niobium into the grain via grain growth probably caused the semiconducting and PTCR character of the niobium-doped BaTiO3.