Positive Temperature Coefficient Of Resistivity Effect Research Articles

Correlation between positive temperature coefficient of resistance, double Schottky barrier, and anionic substituents in BiFeO3

Various types of conduction (leakage current) mechanisms in metal oxides deteriorate the system's electrical response. The existence of impurity phases, the formation of oxygen vacancies, and high porosity are the main source of free charge carriers in the system. Acceptor states are created due to the formation of oxygen vacancies in the system. In BiFeO3, acceptor states are formed within the grains and at the grain boundaries. The formation of double Schottky barriers at the grain boundaries is interpreted to be associated with the formation of such acceptor states formed at the grain boundary. These acceptor states are the consequence of oxygen stoichiometry which is also responsible for the appearance of a positive temperature coefficient of resistance (PTCR). The effect of substituting isovalent and aliovalent dopants in BFO has been comprehensively analyzed in the present study. These substitutions are responsible for forming a double Schottky barrier at the grain boundary. Barrier potential and barrier width are calculated and plotted as a function of the substituent (di, tri, or tetravalent) to highlight the role of the substituent's valence in the formation of a double Schottky barrier at the grain boundary and the appearance of the PTCR effect in the resistivity profile. The present study reveals that the occupation of the acceptor states at the grain boundaries affects the inter-grain conductivity.

Self-Powered Bipolar Photodetector Based on a Ce-BaTiO3 PTCR Semiconductor for Logic Gates.

Ferroelectric materials bring new opportunities for self-powdered photodetectors, taking advantage of their anomalous bulk photovoltaic effect. However, ferroelectric-based photodetectors suffer from relatively poor responsivity and detectivity due to obstacles of low electrical conductivity and low photoelectric conversion ability. The present work proposes a strategy based on heterovalent ion Ce-doping into BaTiO3 (Ce-BTO) that gives rise to a good room temperature conductivity combined with a significant PTCR (positive temperature coefficient of resistivity) effect. By utilizing a Ce-BTO PTCR semiconductor, a high-performance self-powered photodetector ITO/Ce-BTO/Ag is fabricated, demonstrating a polarity-switchable photoresponse with the change of wavelength due to the competition between hot electrons induced by the Ag plasmonic effect and electron-hole pairs separated by a Schottky barrier. Moreover, benefiting from the reduced bandgap and the introduced impurity states, good responsivity (9.85 × 10-5 A/W) and detectivity (1.25 × 1010 Jones) as well as fast response/recovery time (83/47 ms) is achieved under 450 nm illumination. Finally, four representative logic gates ("OR", "AND", "NOR", and "NAND") are demonstrated with one photodetector via the bipolar photoresponse. This work opens an avenue to promote the application of PTCR semiconductors in optoelectronics, offering a conceivable means toward high-performance self-powered photodetectors.

Pyroresistive Properties of Composites Based on HDPE and Carbon Fillers.

Electrothermal processes were studied in pyroresistive composites based on high-density polyethylene (HDPE) containing 8 vol.% carbon black (CB), 8 vol.% carbon fibers (CF), and their mixture 4 vol.% CB + 4 vol.% CF. It is shown that the kinetic heating curves of composites are well described by an exponential dependence with a certain heating rate constant k for each type of composite. After a short heating time, the equilibrium temperature Te is reached in the sample. When the applied voltage exceeds a certain value, the Te value decreases due to the presence of the positive temperature coefficient of resistance (PTC) effect. Due to the PTC effect, the composites exhibit a self-regulating effect relative to the Te. Relations between the applied voltage, electric power, and equilibrium temperature are found, the Te value depends on the applied voltage according to the quadratic law whereas there is a linear relationship between the Te and electric power. A possible application of such pyroresistive composites is resistance welding of plastics using a heating element (HE) made of a pyroresistive material. The use of HDPE-CB composite to create HE for resistance welding is demonstrated and the welded joint of HDPE parts obtained using HE is shown.

Electrical characteristics of Mg doped GeO2 NWs based device

In this article, the growth of a undoped GeO2 and Mg doped GeO2 nanowires (NWs) by electron beam evaporation method and analysis of its electrical properties has been reported. Au/GeO2 and Au/Mg-GeO2NWs based devices on Si substrate was fabricated. The optical band gap (Eg) for both the undoped GeO2 and Mg doped GeO2NWswas estimated to be 3.78 eV and 3.37 eV from UV–Vis spectrum. The temperature dependence current(I)–voltage(V) characteristics of undoped GeO2 based device shows a gradual increase of conductivity with the increase of temperature. Where, Mg doped GeO2NWs based device demonstrates a decreasing nature of conductivity with the increase of temperature. This anomalous characteristic has been explained by the positive temperature coefficient of resistance (PTCR) effect. The temperature dependent ideality factor of Mg doped GeO2NWsand undoped GeO2 NWs devices were studied. The increase in barrier height on increasing of temperature also been observed for the Mg doped GeO2NWs based device. Owing to the PTCR effect, the calculated series resistance of Mg doped GeO2NWs based device also shows an anomalous increasing behavior with the increasing of temperature where as undoped GeO2 based device shows a normal behavior of decreasing of series resistance with increase of temperature.

The Positive Temperature Coefficient of Resistivity in BiFeO3 Films

The use of lead-free ceramic film materials with positive temperature coefficient of resistivity (PTCR) is widespread in temperature heaters and sensors in micro-electromechanical systems. In this research, the out of plane transport properties of the BiFeO3 (BFO) films have been studied. Surprisingly, PTCR was found in the BFO ceramic films due to the strongly correlated interaction between the multiferroic material BFO and the superconductor YBCO perovskite oxides. To our knowledge, this is the first report on the PTCR effect of BFO films. The BFO/YBCO interface and the bulk conductivity of BFO are important for the PTCR effect, as they make it possible to compare the transport properties of Au/BFO/YBCO- and YBCO/BFO/YBCO-type structures. PTCR was observed in Au/BFO/YBCO at a bias voltage of more than 2 V, but not in the YBCO/BFO/YBCO, even with a 40 V bias voltage. PTCR was found after BFO breakdown of a YBCO/BFO/YBCO capacitor. This indicated that the conductivity of BFO is critical for PTCR. The dependence of PTCR on the superconducting transition temperature illustrates that a cooper-pair can be injected into BFO. Our work presents a method by which to produce a lead-free ceramic film material with PTCR.

BaTiO3-based thermistor hollow fibers prepared using a phase inversion spinning process for energy efficient gas sorption

Positive temperature coefficient of resistivity (PTCR) hollow fibers that exhibit self-regulating heating characteristics have potential applications in temperature-swing adsorption systems (TSA), such as CO2 recovery and drying of compressed air. La-doped BaTiO3 hollow fibers displaying a PTCR effect were produced by phase inverting a casting solution consisting of N-methly-2-Pyrrolidone, polymethyl methacrylate, polyvinylpyrrolidone, BaTiO3, TiO2, and La2O3 through a spinneret into a coagulating waterbath. This was followed by polymer debinding, high temperature sintering between 1350−1400 °C and annealing in air at 1175 °C to produce hollow fibers of the composition Ba0.9975La0.0025TiO3. Hydrothermal synthesis was implemented to deposit an adsorbent porous zeolite X layer within the hollow fiber lumen, which was confirmed by electron dispersive X-ray spectroscopy and CO2 adsorption at 0 °C. Hence, these materials can be applied to energy efficient TSA gas separation processes. The results are discussed in terms of hollow fiber microstructure, adsorption characteristics and electrical properties.

Electrical properties of La-Mn-codoped BaTiO3-(Bi0.5Na0.5)TiO3 lead-free PTCR ceramics

La-Mn-codoped 0.97BaTiO3-0.03(Bi0.5Na0.5)TiO3 ceramics (abbreviated as xLa-yMn-BBNT3, x = 0.001, 0.002, 0.003, 0.004; y = 0, 0.0005, 0.001, 0.0015, 0.002) for application of lead-free positive temperature coefficient of resistivity (PTCR) thermistors were prepared using a wet chemical route. The analysis of XRD patterns shows that all prepared powders and ceramics are composed of pure tetragonal perovskite phase. The x = 0.002 La-doped ceramic sintered in air has a Curie temperature of Tc about 140 °C, room-temperature resistivity (ρ25) of ~103 Ω cm and resistivity jump (log(ρmax/ρmin)) of ~3 orders in magnitude. It is also found that the resistivity jump of prepared ceramic reaches up to 4.4 orders in magnitude when y = 0.0015 Mn was doped. Influence of grain and grain-boundary effect on PTCR effect was analyzed by complex impedance spectra measured at different temperatures, and the results reveal that the grain boundary effect plays key role in the PTCR effect.

Electrical properties of n-conducting barium titanate ceramics over a wide temperature range under voltage load

Bulk and grain boundary resistivities as well as grain boundary capacitances of PTCR (positive temperature coefficient of resistivity) thermistors have been investigated as a function of voltage load and temperature ranging from 30 to 820 °C by application of impedance spectroscopy. In addition, current – voltage curves have been measured and the resistivities extracted from these dc measurements are in close agreement with those obtained from impedance spectroscopy. The resistance – temperature characteristics are typical for n-type barium titanate – based PTCR ceramics, viz. a steep increase of the grain boundary resistance above the Curie – temperature (PTCR effect) and decreasing resistance with increasing temperature in the NTC (negative temperature coefficient) regime above approximately 200 °C. The grain boundary capacitance shows a sharp peak at the Curie – temperature (around 120 °C) and obeys the Curie – Weiss law in the paraelectric state. Basically, the grain boundary resistivities decrease significantly under voltage load. However, at elevated temperatures (above 600–700 °C) this non-linear effect vanishes and linear ohmic (or even sub-ohmic) behavior can be observed. The electrical properties can be interpreted in terms of a modified double Schottky barrier model. Reasonable coincidence between simulated and measured current - voltage curves as well as grain boundary conductivities has been found in a wide temperature range (up to 800 °C) under high field conditions (up to an external field strength of 1000 V cm−1).

Influence of Sintering Time on the PTCR Effect of Nb2O5-doped BaTiO3 Ceramics

The effects of the sintering time on the electrical properties and the positive temperature coefficient of resistance (PTCR) effect of Ba1.006(Ti1-xNbx)O3 (BTN) ceramics were investigated, which were sintered at 1190 oC for 0.5-6 hours in a reducing atmosphere and then re-oxidized at 800 oC for 1 hour. The results indicated that the sintering time affected the electrical properties and the PTCR effect of the multilayer BTN samples, whose room-temperature resistance decreased with an increase of the sintering time at same sintering temperature of 1190 oC. However, the resistance jump first increased and then reduced as a function of the sintering time. Furthermore, The BTN ceramics exhibited a pronounced PTCR effect, with a resistance jump greater by 3.6 orders of magnitude, along with a low RT resistance of 0.14 Ω at a reoxidated temperature of 800 oC after sintering at 1190 oC for 2 h in a reducing atmosphere. In addition, the activation energy of samples obtained at different sintering times had also been investigated.

Influence of Ba/Ti ratio on PTCR effect of Bam(Ti1−xNbx)O3 ceramics prepared by the reduction sintering-reoxidation method

In this work, we investigate the influences of Ba/Ti ratio and sintering conditions on the characteristics of positive temperature coefficient of resistance (PTCR) and electrical properties of Ba[Formula: see text](Ti[Formula: see text]Nb[Formula: see text])O3 (BTN) ceramics. The ceramics were fired at 1190[Formula: see text]C for 0.5–6.0 h in a reducing atmosphere and then reoxidized at 600–650[Formula: see text]C for 0–8 h. The Ba/Ti ratio [Formula: see text] affected the electrical properties and PTCR effect of the BTN specimens. The room-temperature (RT) resistance of the BTN samples initially decreased [Formula: see text] and then increased [Formula: see text] as the Ba/Ti ratio increased. Moreover, BTN ceramics exhibit a pronounced PTCR effect, with a resistance jump greater by 3.0 orders of magnitude and a low 0.1 [Formula: see text] RT resistance at a low reoxidation temperature of 600[Formula: see text]C after sintering under a reducing atmosphere. Furthermore, the average sample grain size increased along with the Ba/Ti ratio. In addition, the influence of the sintering time and the reoxidation time on the electrical properties and the PTCR effect were also investigated.

Diode Property and Positive Temperature Coefficient of Resistance of Pt/Al2O3/Nb:SrTiO3

AbstractThe rectification of the Pt/amorphous Al2O3 (a‐AO)/Nb‐doped SrTiO3 (NSTO) structure with excellent applicability as a selector for crossbar array resistive switching random access memory is introduced. The maximum forward/reverse current ratio exceeds 106, and the nonlinearity is also as high as 106 at room temperature. The barrier height at the a‐AO/NSTO interface is investigated via X‐ray photoelectron spectroscopy and is found to be 1.57 eV. The expected conduction mechanism is trap‐assisted tunneling in the forward bias condition. The barrier height at the Pt/a‐AO interface is examined by fitting the current–voltage results at various temperatures according to the Fowler–Nordheim transport mechanism, under the reverse bias condition, and it is found to be 2.75 eV. Moreover, the temperature dependence measurement of the current–voltage characteristics exhibits the positive temperature coefficient of resistance (PTCR) effect in reverse bias. This PTCR effect can be understood from the electron trapping of the acceptor‐like states at the a‐AO/NSTO interface with increasing temperature. The involvement of the PTCR effect under the reverse bias condition and the slight increase in the forward current further enhance the diode performance up to 107 at 70 °C, which is the highly promising performance of the present structure.

Influence of sintering time and donor concentration on the PTCR effect of La-doped BaTiO3-Na0.5Bi0.5TiO3 ceramics

Lead-free positive temperature coefficient of resistivity (PTCR) materials with higher Curie point are important for their high temperature applications. In the present study, 0.99BaTiO3 −0.01Na0.5Bi0.5TiO3-xLa2O3 (99BT-1NBT-100xLa, x = 0.001, 0.002, 0.003, 0.004) ceramics were prepared by a conventional solid-state reaction method. The phase structure, microstructure, and PTCR effect of these ceramics were investigated. X-ray diffraction analysis indicates that all the samples are of a single tetragonal perovskite structure. The SEM images of all samples show the grain shape is irregular. And the grain size is around 3–30 µm. The PTCR effects occur at a temperature of about 150 °C. The room-temperature resistivity (ρ25) drops with the increase of donor concentration and the decrease of sintering time. The resistivity ratio (ρmax/ρmin) first increased and then decreased with increasing sintering time and donor concentration. The optimum composition for a large PTCR effect is 99BT-1NBT-0.3La, having a high jump of resistivity of 2.63 orders of magnitude sintered at 1400 °C for 30 min in air. A possible relation between the PTCR effect with the dopant behavior are discussed. This work may help on the study of lead-free PTCR ceramics from the view of control of doping elements and sintering procedure.

WITHDRAWN: Influence of sintering time and donor concentration on the PTCR effect of La-doped BaTiO3-Na0.5Bi0.5TiO3 ceramics

Abstract Lead-free positive temperature coefficient of resistivity (PTCR) materials with higher Curie point are important for their high temperature applications. In the present study, 0.99BaTiO3 −0.01Na0.5Bi0.5TiO3-xLa2O3 (99BT-1NBT-100xLa, x = 0.001, 0.002, 0.003, 0.004) ceramics were prepared by a conventional solid-state reaction method. The phase structure, microstructure, and PTCR effect of these ceramics were investigated. X-ray diffraction analysis indicates that all the samples are of a single tetragonal perovskite structure. The SEM images of all samples show the grain shape is irregular. And the grain size is around 3–30 µm. The PTCR effects occur at a temperature of about 150 °C. The room-temperature resistivity (ρ25) drops with the increase of donor concentration and the decrease of sintering time. The resistivity ratio (ρmax/ρmin) first increased and then decreased with increasing sintering time and donor concentration. The optimum composition for a large PTCR effect is 99BT-1NBT-0.3La, having a high jump of resistivity of 2.63 orders of magnitude sintered at 1400 °C for 30 min in air. A possible relation between the PTCR effect with the dopant behavior are discussed. This work may help on the study of lead-free PTCR ceramics from the view of control of doping elements and sintering procedure.

Impedance characteristics and PTCR effect in lead free BaTi1-xSnxO3 piezoceramics

BaTi1-xSnxO3 of compositions x = 0.07, 0.08, 0.09, 0.10 and 0.11 are synthesized to study their piezoelectric and impedance characteristics. The studies revealed that the composition x = 0.08 exhibits the maximum piezoelectric coefficient (d33 = 296 pC/N) and remnant polarization (Pr = 6.92 μC/cm2) values. The impedance analysis showed that the depressed semi-circular arc observed in the Nyquist’s plots gave evidence for the existence of non-Debye type relaxation behavior in the compounds. The impedance studies suggested a possible correlation between the d33 and microstructural properties. The activation energies extracted from ac conductivity plots strongly indicate the existence of defect dipole assisted conductivity mechanism in the samples. Notably, the samples displayed positive temperature coefficient of resistance (PTCR) just above their ferroelectric transition. The frequency dependent ac conductivity follows the Jonscher’s universal power law. The dominant conduction mechanism in the samples is determined to be the small polaron hopping mechanism.

The influence of calcination temperature on the PTCR effect in (Bax-0.002Sm0.002) TiO3 ceramics prepared by the reduction sintering-reoxidation method

We investigate the effect of calcination temperature on the positive temperature coefficient of resistivity (PTCR) characteristics in (Bax-0.002Sm0.002)TiO3 ceramics that were fired at 1250 °C for 30 min in a reducing atmosphere and reoxidized at 800 °C for 1 h in air. The results indicate that the room-temperature resistivity first decreased and then increased as calcination temperature increased from 1000 °C to 1200 °C. Moreover, the critical calcination temperature of 1150 °C is experimentally determined. The samples have a low room-temperature resistivity of 38.4 Ω·cm and exhibit a significant PTCR effect with a resistance jump of 2.1 orders of magnitude. Furthermore, the room-temperature resistivity of the S7 samples doped with a small amount of Mn(NO3)2 is much higher than that of the S3 specimens not doped with Mn(NO3)2 in our work.

Influence of Reoxidation Time on Electrical Properties of Y2O3-doped BaTiO3 Ceramics Sintered in a Reducing Atmosphere

The influence of the reoxidation time on electrical properties and the positive temperature coefficient of resistance (PTCR) effect in multilayer Y2O3-doped BaTiO3 (BTO) ceramics were investigated. The BTO ceramics were sintered at 1160 °C−1270 °C for 2 h in a reducing atmosphere and then reoxidized at 500 °C–900 °C for 0 h−4 h. Results indicated that the room-temperature resistance of BTO ceramics reoxidized at 750 °C for 2 h after sintering at 1160 °C−1270 °C for 2 h decreased with the increasing of the sintering temperature. As the reoxidation time increased, the room-temperature resistance of the BTO samples slightly increased. In addition, the effect of the reoxidation time on the PTCR effect of the ceramics was also studied. The BTO ceramics had a low room-temperature resistance of 0.3 Ω and a resistance jump greater than 3.0 orders of magnitude.

Investigation of PTCR effect and microdefects in Nb2O5-doped BaTiO3-based ceramics by positron annihilation techniques

The influence of Nb2O5-doped concentration on the positive temperature coefficient of resistance (PTCR) effect, electrical properties and microdefects of (Ba[Formula: see text]Sr[Formula: see text])(TiNb[Formula: see text])O3 (BSTN) ceramics were investigated. Firing was conducted at 1350[Formula: see text]C for 2 h in air. The donor-doped content affected the electrical properties, PTCR effect and formation of the microdefect type of the BSTN samples. The room temperature resistivity of the BSTN specimens first decreased and then increased with increasing donor-doped content in the range of 0.2 mol.% Nb[Formula: see text] to 0.5 mol.% Nb[Formula: see text]. Moreover, the information on microdefects in BSTN ceramics was demonstrated by coincidence Doppler broadening spectrum. The influence of the defects on the PTCR characteristics of the ceramics was also revealed.

Influence of sintering process on electrical properties and PTCR effect of laminated Ba1.005(Ti1−xNbx)O3 ceramics fired in a reducing atmosphere

This study investigates the influence of dopant content and firing conditions on electrical properties and positive temperature coefficient of resistance (PTCR) effect of Ba[Formula: see text](Ti[Formula: see text]Nb[Formula: see text]O3 (BTN) ceramics sintered at different temperatures from 1070[Formula: see text]C to 1220[Formula: see text]C for 2 h in a reducing atmosphere and reoxidized within the temperature range of 600[Formula: see text]–[Formula: see text]750[Formula: see text]C for 0.5[Formula: see text]–[Formula: see text]8 h. The results indicate that the room-temperature (RT) resistance of the laminated BTN specimens initially decreased and then increased as a function of the dopant concentration. Moreover, the resistance jump exhibited a contrasting tendency. Furthermore, the RT resistance of the BTN samples rapidly decreased at first and then gradually decreased with increasing sintering temperature. Meanwhile, the resistance jump of the samples increased first and then decreased. In addition, the influence of reoxidation times on the PTCR characteristics of ceramics was investigated.

Influence of Cooling Duration on the PTCR Effect of Sm3+-doped BaTiO3-based Ceramics Sintered in a Reducing Atmosphere

The influence of cooling duration on the electrical properties and the positive temperature coefficient of resistance (PTCR) characteristics of Sm-doped BaTiO3 (BST) ceramics fired at 1200 °C for 30 min in a reducing atmosphere and deoxidized at 800 °C for 1 h were investigated. The cooling duration influenced the PTCR characteristics of the BST specimens. The room-temperature resistivity of the samples firstly reduced and then increased with the increase in the content of Sm2O3. A long cooling duration resulted in low resistivity of the BST ceramics. Meanwhile, the room-temperature resistivity of the BST ceramics decreased with an increase in cooling duration. Furthermore, the S2 samples exhibited a remarkable PTCR effect. The samples exhibited a resistance jump greater than 3.2 orders of magnitude and a low room-temperature resistivity of 228.4Ω·cm.

Influence of sintering method on the PTCR effect and microstructures of Sm 2 O 3 -doped BaTiO 3 -based ceramics sintered in a reducing atmosphere

Abstract This study investigated the effects of sintering temperature and cooling rates on the positive temperature coefficient of resistance (PTCR) effect and microstructures of Ba 1.022 – x Sm x TiO 3 (BST) ceramics sintered at 1200 °C−1260 °C for 30 min in a reducing atmosphere and reoxidized at 700 °C−900 °C for 1 h. The sintering temperature and cooling rates influenced the PTCR effect and microstructure of the BST samples. The resistivity of the samples at room temperature initially decreased and then increased with the increase in the content of Sm 2 O 3 . A high sintering temperature resulted in low resistivity of the BST ceramics. Meanwhile, the resistivity of the specimens at room temperature increased with the increase in cooling rates. Furthermore, a rapid cooling rate exerted a significant PTCR effect. The samples exhibited a resistance jump greater than 3.0 orders of magnitude and a low room-temperature resistivity. The behaviour of the microstructure of the as-fired BST ceramics cooled at different rates was also investigated.