PTCR Effect Research Articles

Synthesis of materials based on (1-x)BaTiO3-x(Bi0.5K0.5)TiO3 exhibiting the PTCR effect

Synthesis of materials based on (1-x)BaTiO3-x(Bi0.5K0.5)TiO3 exhibiting the PTCR effect

Influence of doping BiYO 3 and Nb 2O 5 on PTCR characteristics of BaTiO 3 thermistor ceramics

Nb 2O 5-doped (1 − x)Ba 0.96Ca 0.04TiO 3– xBiYO 3 (where x = 0.01, 0.02, 0.03 and 0.04) lead-free PTC thermistor ceramics were prepared by a conventional solid state reaction method. X-ray diffraction, scanning electron microscope, Agilent E4980A and resistivity-temperature measurement instrument, were used to characteristic the lattice distortion, microstructure, temperature dependence of permittivity and resitivity-temperature dependence. It was revealed that the tetragonality c/ a of the perovskite lattice, the microstructure and the Curie temperature changed with the BiYO 3 content. In order to decrease the room temperature resistivity, the effect of Nb 2O 5 on the room temperature resistivity was also studied, and its optimal doping content was finally chosen as 0.2 mol%. The 0.97Ba 0.96Ca 0.04TiO 3–0.03BiYO 3–0.002Nb 2O 5 thermistor ceramic exhibited a low ρ RT of 3.98 × 10 3 Ω cm, a typical PTCR effect of ρ max/ ρ min > 10 3 and a T c of 153 °C.

Electrical Properties of Nd-Doped BaTiO3 PTC Ceramics Prepared by Hydrothermal Synthesis

Nd-doped BaTiO3 nanopowders with ca. 200 nm in average diameter were prepared by hydrothermal synthesis at 200 and 240 °C for 24 h. Neodymium (III) nitrate hexahydrate (Nd(NO3)3·6H2O) as a donor dopant was added to the powder mixtures of barium hydroxide (Ba(OH)2) and titanium dioxide (TiO2) ranging from 0.25 to 0.45 mol%. A green compact of the powder mixtures obtained was heated at 1340 °C for 2 h with/without three steps of ramp heating processes. Sintered without these steps, 0.35 mol% Nd-doped BaTiO3 with the resistivity of 124 ohm·cm at R. T. indicated insufficient PTCR effect; resistance change of 3 × 102 in the vicinity of Curie temperature. On the other hand, a pellet of 0.35 mol% Nd-doped BaTiO3 sintered via the step-heating process exhibited the large resistance change of 7.5 × 103.

Electrical properties of lanthanum doped barium titanate ceramics

Pure and lanthanum doped barium titanate (BT) ceramics were prepared by sintering pellets at 1300 °C for 8 h, obtained from nanopowders synthesized by the polymeric precursor method. XRD results showed formation of a tetragonal structure. The presence of dopants changed the tetragonal structure to pseudo-cubic. The polygonal grain size was reduced up to 300 nm with addition of lanthanum as a donor dopant. Determined dielectric properties revealed that lanthanum modified BT ceramics possessed a diffused ferroelectric character in comparison with pure BT that is a classical ferroelectric material. In doped BT phase transition temperatures were shifted to lower temperatures and dielectric constant values were much higher than in pure BT. A modified Currie Weiss law was used to explore the connection between the doping level and degree of diffuseness of phase transitions. Impedance spectroscopy measurements were carried out at different temperatures in order to investigate electrical resistivity of materials and appearance of a PTCR effect.

카본블랙을 첨가하여 제조한 다공성 BaTiO3계 세라믹스의 미세구조 및 PTCR 특성 변화

As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr)<TEX>$TiO_3$</TEX> powder. Porous (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics were prepared by pressureless sintering at <TEX>$1350^{\circ}C$</TEX> for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics were investigated. The porosity of porous (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from <TEX>$7.51\;{\mu}m$</TEX> to <TEX>$5.96\;{\mu}m$</TEX> with increasing carbon black contents. PTCR jump of the (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics prepared by adding carbon black was more than <TEX>$10^5$</TEX>, and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics prepared by adding 40 vol% carbon black showed an excellent value of <TEX>$9.68{\times}10^5$</TEX>, which was above two times higher than that in (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr)<TEX>$TiO_3$</TEX> ceramics. It was considered that carbon black is an effective additive for preparing porous <TEX>$BaTiO_3$</TEX> based ceramics. It is believed that newly prepared (Ba,Sr)<TEX>$TiO_3$</TEX> cermics can be used for PTC thermistor.

PTCR effect in carbon black/copolymer composites

Some materials show an abrupt increase in resistivity when the temperature changes only over a few degrees. This phenomenon, known as PTCR effect (positive temperature coefficient of resistivity), has been largely studied in the last few years, due to its potential applications in industry. Particularly, it can be used in auto controlled heaters, temperature sensors, protection circuits and in security systems for power electronic circuits. In this work we present the study of the electrical properties of the percolating system carbon black particles filled with ethylene butylacrylate copolymer composite (EBA), in the temperature range from −100 to 100 °C and in frequencies between 10 Hz and 100 kHz. The PTCR effect was observed at temperatures slightly above the room temperature, for concentrations higher than that of the percolation critical concentration. The mechanism responsible for the change in resistivity, at this stage, is predominantly tunnelling, wherein the conductive filler particles are not in physical contact, and the electrons tunnel through the insulating gap between them. At low temperatures, such as below and close to the glass transition temperature, the DC conductivity obeys the Arrhenius law. The calculated activation energy values are independent of carbon black contents inside the copolymer matrix, suggesting that these particles do not interact significantly with the chain segments of the macromolecules in the EBA copolymer.

Study on the Ordered Structure and Electrical Properties of Ba0.85-xCa0.15(Bi1/2Na1/2)xTiO3 Ceramics

The PTCR ceramic materials with composition of Ba0.85-xCa0.15(Bi1/2Na1/2)xTiO3 have been synthesized in air and in N2 atmosphere at 1350□, respectively. In the XRD spectra, there appears three diffraction peaks in the range of 2θ = 18–23° and the Raman shift at 302.1 cm−1 becomes weak when the samples are re-annealed at 1250□ in air. It is speculated that the ordered distribution of Ba, Ca, Na and Bi in A-site contributes to the new appeared diffraction peaks. The samples sintered in flowing N2 display a relatively low room-temperature resistivity and the PTCR effect can be enhanced after re-annealing in air.

Precision Measurement of PTCR Effect

We report a result in conduction of PTCR component. We measure it under heating and cooling respectively. As the result, the result that the conductivity under heating and that under cooling differed was obtained. And the offset current also had such a hysteresis. Moreover, by the measurements in the range of 10 μV to 10 mV, the result that the temperature characteristic of the conductivity is not dependent on voltage was obtained.

PTCR effect of solid solutions based on the (1-x)BaTiO3–xNa0.5Bi0.5TiO3 system

PTCR effect of solid solutions based on the (1-x)BaTiO3–xNa0.5Bi0.5TiO3 system

The Positive Temperature Coefficient of Resistivity Effect in the Pb(Fe1/2Nb1/2)O3Ceramics Admixed with Lithium

In the paper technological conditions were looked for to obtain the Pb(Fe1/2Nb1/2)O3 (PFN) ceramics and the PFN ceramics with the lithium admixture with the highest electric conduction and conditions appropriate for the PTC-R effect formation. Measurements of dc electrical resistivity, dielectric permittivity and dielectric loss were made as functions of temperature from room temperature to 190◦C, at 1 kHz. The best set of values of dielectric loss and dielectric constant, from the ferroelectricity point of view, were obtained when the precursor with orthorhombic structure was employed. By creating appropriate technological conditions in the PFN ceramics the PTC-R effect can occur above the Curie temperature. Their electric properties are determined by presence of a basic phase of the potential barrier on the grain boundaries.

Influence of Rare Earth on the Electrical Properties and Microstructure of Barium Titanate Ceramics

The ceramic samples of BaTiO3+½xLn2O3+2mol%TiO2 (0.001≤x≤0.01) were prepared, where Ln is Y, Dy, Ho, Er or Y. The influence of rare earth on the resistivity and microstructure of the samples was investigated by the means of XRD, SEM and electric properties testing. The results showed that the resistivity of La-doped sample decreases when x= 0.003 compared with the undoped sample. However, the range of dopant concentration with Dy, Ho, Er or Y for semiconducting samples is wider, especially for Y-doping. Minimum resistivity at room temperature was observed when x=0.003, which is named after the critical concentration. The experimental results indicated that below the critical concentration of Dy, Ho, Er or Y, the substitution took place in the barium sublattice with electronic compensation, and the rare earth ions began to substitute for titanium gradually above the critical concentration. For Ho-doped BaTiO3 ceramic, the resistivity jump (PTCR effect) near the Curie temperature was the highest in the case of x=0.003. Fine-grained structure of the sample doped with 0.6mol% Dy led to the increase of breakdown field strength and dielectric constant of ceramic samples.

Very Low-Temperature, Gram-Scale Synthesis of Monodisperse BaTiO3 Nanocrystals via an Interfacial Hydrolysis Reaction

AbstractA vapor diffusion sol-gel method is reviewed for the preparation of high-quality BaTiO3 nanocrystals on the gram scale at very low temperatures. The synthesis is based on the kinetically controlled introduction of water into a solution of the bimetallic alkoxide, BaTi(O2C4H9)6, where slow hydrolysis then occurs at the vapor-solution interface followed by nucleation and nanocrystal growth at 16 °C. The resulting 6-nm, quasi-spherical nanocrystals are both monodisperse (without stabilizing agents or size selecting purification) and highly crystalline (without any post-synthesis heat treatment), and are isolated in yields near 100%. Based on new permittivity and calorimetry data, the crystal structure of the nanocrystals is most likely in the paraelectric cubic phase (space group Pm3m) at room temperature, which corroborates previous diffraction data. It was also demonstrated that the BaTiO3 nanocrystals can be doped with trivalent lanthanum cations using the same low-temperature vapor diffusion sol-gel method to yield donor-doped Ba1−xLaxTiO3, which exhibits a considerable PTCR effect.

Properties of barium-strontium titanate PTCR ceramics sintered on different powder beds

Barium-strontium titanate (BST) ceramics, co-doped with Sb and Mn oxides, were sintered on different powder beds: Sb-doped BST; Al2O3; or Sb,Mn-codoped BST powder. Phase formation, microstructure and the electrical properties of the samples were analysed. The PTCR behavior depended significantly on the type of powder bed used. The BST ceramic pellet sintered on the Sb-BST powder displayed the largest PTCR effect, with a ρmax/ρRT ratio of ∼106. This was an order of magnitude greater than for samples sintered on the other two powders. Complex impedance analysis confirmed that this was due to a large increase in grain boundary resistance at 250 °C.

Influence of Rare Earths on Electric Properties and Microstructure of Barium Titanate Ceramics

The influence of rare earths on electrical resistivity and microstructure of barium titanate ceramics doped with rare earth ions Y, Dy, Ho, Er and Y at the concentrations of x = 0.001 × 0.01 was investigated by the means of X-ray diffraction, scanning electron microscopy and electric properties testing. The results showed that a dramatic decrease in resistivity occurred at the concentration of 0.3% of La-doped sample. However, the range of concentration for semiconducting samples doped with Dy, Ho, Er and Y was wider, especially for Y-doping. The experimental results indicated that below the critical concentration of Dy, Ho, Er and Y, the substitution took place in the barium sublattice with electronic compensation, above the critical concentration, gradually the rare earth ions began to substitute for titanium. As for Hodoped BaTiO 3 ceramic, the resistivity jump (PTCR effect) near the Curie temperature was the highest in case of lower dopant concentration of 0.3%. Fine-grained structure of sample doped with 0.6% Dy led to the increasing of breakdown electric field strength and dielectric constant of ceramic samples. In contrast, coarsed-grained structure of sample doped with 0.3% Dy showed semiconducting property.

PTCR effect in Li0.12Na0.88Ta y Nb1−y O3 ferroelectric solid solutions

Ceramic samples of Li0.12Na0.88Ta y Nb1−y O3 ferroelectric solid solutions reduced in vacuum in order to raise their electronic conductivity are shown to have a large positive temperature coefficient of resistance in the range 350–400°C, near the superionic transition temperature of analogous unreduced ceramics. This behavior is interpreted in terms of the interplay between electronic and ionic transport processes.

Compositional analysis and electrical properties of Sb, Mn-doped barium strontium titanate PTCR ceramics with TiO2 and SiO2 sintering additives

The secondary phase compositions in Sb-doped (Ba, Sr)TiO3 ceramics containing SiO2 and excess TiO2 sintering additives have been examined by XRD, BEI and EPMA techniques. It is shown that alongside the primary (Ba0.797Sr0.2Sb0.003)TiO3 phase, (Ba1.95Sr0.05)2(Ti1.2Si1.8)O8 and Sb-doped (Ba0.99Sr0.01)6Ti17O40 phases form at the intergranular regions. Substitution of up to 0.04 mol% MnO2 enhances the PTCR effect, giving a ratio ρmax/ρmin ∼ 7 × 105 for the optimum 0.04% MnO2 composition. At this level Mn cannot be detected in the microstructure by EPMA, however in insulating samples containing 0.08 mol% of MnO2, it was detected in the (Ba0.99Sr0.01)6Ti17O40 intergranular phase.

PTCR effect in BaBi2Nb2O9-doped BaTiO3 ceramics

The influences of BaBi2Nb2O9 content on the electrical property and the microstructure of BaTiO3-based materials have been studied. With an increase in BaBi2Nb2O9 content the grain size decreases. All the prepared BaBi2Nb2O9 doping BaTiO3-based thermistors show typical PTC effect. As the amount of BaBi2Nb2O9 added in BaTiO3-based ceramics increases, resistivity appears to exhibit a minimum value. At high BaBi2Nb2O9 content (≥0.0875), the resistivity increased again with increasing BaBi2Nb2O9 content. At a given content of BaBi2Nb2O9, the influence of sintering temperature on the electrical properties of samples has been investigated. A minimum of room temperature resistivity is obtained at the sintering temperature equal to 1,290 °C at a given content of BaBi2Nb2O9.

PTCR effect in Mn-doped BT-BNT Semiconducting Ceramics

PTCR effect in Mn-doped BT-BNT Semiconducting Ceramics

PTCR effect in BaBiO 3-doped BaTiO 3 ceramics

BaBiO 3 shows, at room temperature, a distorted perovskite lattice with monoclinic unit cell ( I2/m) characterized by two different B sites, occupied respectively by Bi 3+ and Bi 5+. The influences of BaBiO 3 content on the electrical property and the microstructure of BaTiO 3-based materials have been studied. At a low dopant concentration the grain size is not influenced significantly by the donor concentration. With an increase in BaBiO 3 content the grain size decreases rapidly. All the prepared BaBiO 3 doping BaTiO 3-based thermistors show typical PTC effect. As the amount of BaBiO 3 added in BaTiO 3-based ceramics increases, resistivity appears to exhibit a minimum value. At high BaBiO 3 content (≥ 0.3), the resistivity increased again with increasing BaBiO 3 content. At a given content of BaBiO 3, the influence of sintering temperature on the electrical properties of samples has been investigated. A maximum of ρ max/ ρ min ratio was obtained at the sintering temperature equal to 1290 °C at a given content of BaBiO 3.

Barrier Layer Formation and PTCR Effect in (1 − x) [Pb(Fe1/2Nb1/2)O3]-xPbTiO3(x= 0.13) Ceramics

(1 − x)Pb(Fe 1/2 Nb 1/2 )O 3 -xPbTiO 3 (PFN-xPT) ceramics with x = 0.13 sintered at 1200°C show diffuse phase transition and very high dielectric constant at lower frequencies. The high value of dielectric constant at lower frequencies is shown to be due to the barrier layer formation. The resistivity of the PFN-xPT ceramics, obtained by complex impedance analysis, initially decreases with temperature and then shows an upward trend beyond the ferroelectric Curie point reminiscent of BaTiO 3 based thermistors with PTCR effect.