PTCR Effect Research Articles

The apparent PTCR effect in layered alkali titanates - A correlation between temperature dependent electrical properties and thermal analyses

Adsorbed water promotes proton conduction in ceramics at ambient conditions prior to its evaporation, apparently leading to the positive temperature coefficient of resistivity (PTCR) effect. Using surface water-containing Cs2Ti6O13 (1.8 mol water/mol titanate) as an example, the static conductivity (at 50 °C) of ∼10−5 S cm−1 is one thousand times that at 200 °C due to the enhanced proton conduction. At 50–150 °C, the conductivity decreases by 4 orders of magnitude because water evaporation decreases the number of charge carriers. At 150–400 °C, the conduction in water-free Cs2Ti6O13 is thermal-activated with the apparent activation energy Ea ∼58–72 kJ mol−1, depending on the formalisms. We show clearly that an endothermic DSC peak (water evaporation) in Cs2Ti6O13 coincides with all eight presentations of AC properties examined. Similar correlations are obtained from the TG/DTG curves in Cs2Ti5O11·H2O containing mostly intercalated water. The correlation between thermal analyses and AC properties points out that water molecules essentially contribute to the charge transport at ambient conditions of layered alkali titanates. This scenario might be potentially extended to other humidity-sensitive ceramics.

The jump-like PTCR effect in Ca1-xYxCu3Ti4O12 ceramics hot quenched under high-pressure

The PTCR effect is an important application phenomenon in the ferroelectric BaTiO3 electronic ceramic materials. In this work, the PTCR effect is also found in high pressure (HP) hot quenched Ca1-xYxCu3Ti4O12 (CYCTO) ceramics. Compared with the pure CaCu3Ti4O12 (CCTO) ceramic synthesized under ordinary pressure (OP), the low temperature resistivity of HP CYCTO samples is about 3 orders of magnitude lower than that of untreated CCTO samples, showing an obvious PTCR effect. The transition temperature is close to 178 K for x = 0.2 sample. The analysis of crystal and magnetic structures shows that the crystal and magnetic structures of HP CYCTO samples do not change before and after the resistance transition. X-ray photoelectron spectroscopy showed that the concentration of oxygen vacancy defects in HP CYCTO is higher than CCTO. By analyzing the conduction behaviors of HP CYCTO samples, it suggests that oxygen vacancies and Y3+ ions may be the important donors for the decrease of low temperature resistivity of HP CYCTO samples. The results in this work have important reference value for the application of the electrical conduction behaviors in CCTO.

Solvothermal synthesis of nanoscale BaTiO3 in benzyl alcohol-water mixtures and effects of manganese oxide coating to enhance the PTCR effect.

A solvothermal method using various benzyl alcohol/water solvent mixtures has been used to synthesise phase pure nanocrystalline BaTiO3 samples with varying particle sizes in the range of 11-139 nm. The crystallite/particle size of BaTiO3 shows an overall decrease as the benzyl alcohol percentage increases, especially at higher percentages (≥80%) of benzyl alcohol. The decrease in crystallite/particle size can be attributed to the increased viscosity of the solvent mixture when raising the percentage of benzyl alcohol. A manganese oxide coating applied to the BaTiO3 surface had a negligible impact on its microstructure and morphology, but significantly enhanced the observed positive temperature coefficient of resistance. This research has been carried out to allow the development of smaller BaTiO3 particles for use in new battery, capacitor and thermistor technologies, whilst maintaining the PTCR property of the material that is typically observed in larger particle sizes.

Enhanced Ptcr Effect of (Ba,Pb)Tio3-Based Ceramics by Appropriate Al2o3 Addition

Enhanced Ptcr Effect of (Ba,Pb)Tio3-Based Ceramics by Appropriate Al2o3 Addition

Defect chemistry of donor-doped BaTiO3 with BaO-excess for reduction resistant PTCR thermistor applications - redox-behaviour.

The electrical conductivity of donor-doped BaTiO3 thermistor ceramics with excessive BaO revealing a reduction-persistent PTCR effect has been carefully examined depending on materials' composition and oxygen partial pressure at moderate temperatures between 973 and 1273 K. This thermal regime represents the range which is relevant for the realization of insulating grain boundaries in these electrically inhomogeneous ceramic materials through reoxidation. Based on the experimental results strong evidence for a general correlation between the PTCR characteristics, DC-conductivity and the herewith associated defect chemistry significant to thermistor applications is presented for the system (Ba, La)mTiO3, where m designates the BaO-excess (m≥ 1). Nominal compositions with a relatively low (Ba + La)/Ti ratio m only show a rather poor PTCR effect and an overall donor-type response in conductivity can be observed at all levels of oxygen partial pressure considered in the present study. With increasing (Ba + La)/Ti ratio m the nonlinear resistivity jump with increasing temperature strongly improves and the acceptor-type behaviour seems to dominate the total conductivity at partial pressures of oxygen above approximately 10-6 MPa. This result for compositions with high BaO-excess can be understood by the local formation of point defect associates in the grain boundary regions that consist of both acceptor-type titanium vacancies and donor-type oxygen vacancies. Their origin is attributed to the preferential local incorporation of excessive BaO into the BaTiO3 lattice at the intergranular interfaces.

Dielectric, impedance relaxation and DC resistivity studies on microwave sintered Ba1-xRexTiO3(Re = Nd&Pr) ceramics using 5% SiO2 as sintering aid

ABSTRACTBa1-xRexTiO3 ceramics (Re = Nd&Pr with x = 0.002 & 0.004) were prepared through microwave sintering route using 5% SiO2 as sintering aid. The dielectric, impedance and DC resistivity studies were carried out over a wide range of temperature. From dielectric studies, it is observed that the transition temperature increased with the substitution of rare earth ions. The room temperature dielectric constant for the Nd (x = 0.002) doped barium titanate is higher when compared to other compositions and the value is 13,600.28. Impedance studies revealed relaxation behaviour. In the present study grain, grain boundary and sample-electrode effects were separated out by using Cole-Cole data. From the DC resistivity studies, it is observed that Pr (x = 0.004) doped barium titanate ceramic showed one order of magnitude PTCR effect.

Electric and dielectric properties of (Ba0.6Pb0.4)TiO3 ceramics modified with special glass in the range of phase transition

Perovskite ceramics (Ba0.6Pb0.4)TiO3 modified with PbO-B2O3-Al2O3-WO3 special glass was prepared with the conventional mixed oxide method. X-ray diffraction analysis (XRD) of the obtained materials confirmed singlephase and pure tetragonal structure. The Rietveld method was used to determine unit cell parameters. Uniform deformation of the tetragonal parameter was observed with addition of the glass. Dielectric measurements revealed the remarkable influence of special glass admixture on the value of dielectric permittivity and dielectric losses, as well as the Curie temperature. However, the most important achievement of the investigations is obtaining a significant PTCR effect in the sample containing 6 wt.% of special glass admixture.

S.13.03 - Novel psychoactive substances: how to understand the acute toxicity associated with the use of these substances

This paper proposed a two-stage thermal processing method combined with the reduction-reoxidation procedure. Samples were firstly sintered in a reducing atmosphere by two stages and then reoxidized in air. Such two-stage thermal processing method was used to adjust density and grain size of ceramics separately. Finally, nanocrystalline semiconducting donor-doped BaTiO3 ceramics were first successfully prepared. Samples with average grain size of 340 nm exhibited unexpectedly low room resistivity of 136 Ω cm and a significant PTCR effect, with a resistance jump of 4 orders of magnitude. In addition, depletion layer thickness of 40 nm and surface acceptor-state densities of 9.52 × 1013 cm−2 were also calculated. Such good properties had not been reported in former publications. It also means that smaller components based on semiconducting BaTiO3 ceramics could be produced and more extensive application field could be proposed in the trend of miniaturization of electronic devices.

Dielectric relaxor, impedance relaxor, PTCR and electromechanical effects in multifunctional ceramic: [Ba(Nd0.1Ti0.8Nb0.1)O3]0.65[Na0.5Bi0.5TiO3]0.25[BaZrO3]0.10

ABSTRACT[BaNd0.1Ti0.8Nb0.1O3]0.65[Na0.5Bi0.5TiO3]0.25[BaZrO3]0.10 (BNNT-NBT-BZ) ceramic is prepared through solid state sintering method. The dielectric, impedance and DC resistivity studies are carried out as a function of temperature. Dielectric and impedance studies revealed relaxor behaviour. DC resistivity studies revealed PTCR effect in the present ceramic. Capacitance resonance and anti-resonance studies in free and clamped state are carried out over a wide range of frequency at room temperature. The values of Kt, Keff and d33 at room temperature are 0.112, 0.105 and 1.003 pm.V−1 respectively for ceramic sample studied under free state, whereas for the samples studied under clamped state the values are 0.667, 0.629 and 26.410 pm.V−1 respectively. Stress and temperature induced modulus resonance and anti-resonance studies are carried out over a wide frequency range and temperature. The values of Kt, Keff and d33 at 723K are 0.99926, 0.99911 and 14.188 nm.V−1 respectively.

Nanocrystalline semiconducting donor-doped BaTiO3 ceramics for laminated PTC thermistor

This paper proposed a two-stage thermal processing method combined with the reduction-reoxidation procedure. Samples were firstly sintered in a reducing atmosphere by two stages and then reoxidized in air. Such two-stage thermal processing method was used to adjust density and grain size of ceramics separately. Finally, nanocrystalline semiconducting donor-doped BaTiO3 ceramics were first successfully prepared. Samples with average grain size of 340nm exhibited unexpectedly low room resistivity of 136Ωcm and a significant PTCR effect, with a resistance jump of 4 orders of magnitude. In addition, depletion layer thickness of 40nm and surface acceptor-state densities of 9.52×1013cm−2 were also calculated. Such good properties had not been reported in former publications. It also means that smaller components based on semiconducting BaTiO3 ceramics could be produced and more extensive application field could be proposed in the trend of miniaturization of electronic devices.

Effect of Semiconductor Element Substitution on the Electric Properties of Barium Titanate Ceramics

Abstract The investigated ceramics were prepared by a solid-state reaction from simple oxides and carbonates with the use of a mixed oxide method (MOM). The morphology of BaTi0.96Si0.04O3 (BTSi04) ceramics was characterised by means of a scanning electron microscopy (SEM). It was found that Si+4 ion substitution supported the grain growth process in BT-based ceramics. The EDS results confirmed the high purity and expected quantitative composition of the synthesized material. The dielectric properties of the ceramics were also determined within the temperature range (ΔT=130-500K). It was found that the substitution of Si+4 ions had a significant influence on temperature behavior of the real (ε’) and imaginary (ε”) parts of electric permittivity as well as the temperature dependence of a.c. conductivity. Temperature regions of PTCR effect (positive temperature coefficient of resistivity) were determined for BTSi04 ceramics in the vicinity of structural phase transitions typical for barium titanate. No distinct maximum indicating a low-temperature structural transition to a rhombohedral phase in BTSi04 was found. The activation energy of conductivity was determined from the Arrhenius plots. It was found that substitution of Si ions in amount of 4wt.% caused almost 50% decrease in an activation energy value.

The Influence of Sintering Atmosphere and Reoxidation Temperature on the Electrical Properties of the Chip-Type Ba<sub>1-<i>x</i></sub>Sm<i><sub>x</sub></i>TiO<sub>3</sub> Based Ceramics

The PTCR characteristics of (Ba1-xSmx)TiO3(BSMT) with different donor-doped concentration (x) sintered in a reducing atmosphere and reoxidized in air are investigated. The results reveal that the room temperature resistivity (ρRT) of the semiconducting BSMT ceramics first decreases and then increases with increasing of thexvalues, especially whenxis 0.004, the semiconducting BSMT ceramics reoxidized at 850oC for 1 h after sintering at 1300 °C for 30 min in a reducing atmosphere achieve a lower room temperature resisitivity of 82.6 Ωcm. in addition, the doped 0.1 mol% Sm3+BSMT samples fired at 1300 °C for 30 min in air exhibit remarkable PTCR effect with a resistance jumping ratio of 3.4 orders magnitude; moreover, a lower ρRTof the BSMT specimens sintered in a reducing atmosphere is obtained.

PTCR anomaly in barium-titanate-based composites

We have identified a PTCR anomaly in undoped BaTiO3 (BT) ceramics. This anomaly was ascribed to a disconnection of the semiconducting grains, due to dimensional changes of the BT grains at the Curie point, in a composite composed of two constituent BT phases, one with a low electrical resistivity and the other with a high electrical resistivity. The composite exhibits a significant PTCR effect of three orders of magnitude at the Curie temperature.Using a similar approach, a PTCR anomaly was observed in a composite where copper was used as the conductive matrix, while BT particles were used as the second constitutive phase in the composite, acting as a circuit-breaker, and disconnecting the continuous conducting phase at the Curie temperature.

Microstructures and Electrical Properties of BaTiO<sub>3</sub> PTC Ceramics

The microstructure, especially porosity, of PTC (positive temperature coefficient) thermistor based on BaTiO3 was controlled with a forming pressure. The relationship between theirPTCR properties and microstructureswas investigated with an optical and SEM (Scanning Electron Microscope) images and digital multimeter. Disk samples were fabricated by pressinguniaxially at various pressures of 100~15000kg/cm2 and sintering at 1265°C in reducing atmosphere and finally re-oxidizing at 700°C in air. The porosity of the samples decreased rapidly from 45% to 8% with increasing the forming pressure from 100 to 1000kg/cm2andbecame 4% at 15000kg/cm2with slowdecreasing of porosity in the pressure range of 1000~15000kg/cm2.With increasing the forming pressure, the resistivity jump of samplesdecreased rapidlyfrom 0.5 to 2.9 at about1000kg/cm2that corresponds tothe porosity of 15% and was saturated above this pressure. It is considered that there is a critical amount of porosity for having PTCR effect, which was about 15% in our samples. In addition, the porosity of the sample has a greater influence on the resistivity jump than on theresistivity at room temperature, which is due to the oxidation of grain boundary through a favorable channel of oxygen such as a pore.

The PTCR Effect Induced by Grain Boundary Segregation in Acceptor

The conductive properties of donor doped BaTiO3 semiconductor ceramic was studied with a quantitative model in this paper. Considering the influence of acceptor grain boundary segregation, a differential equation of electron level was established. According to a four order Runge-Kutta formula, the energy level of the grain boundary barrier was obtained at different temperatures numerically. Further, the PTCR effect of BaTiO3 semiconductive ceramics was calculated.

Effect of Reoxidation Temperature on Electrophysical Properties of High-T<sub>C</sub> Barium Titanate-Based PTCR Ceramics

Ceramic samples of (1 x)BaTiO3–xNa0.5Bi0.5TiO3 system were prepared by sintering in reducing atmosphere of N2/H2 and were subsequently reoxidized in air. The influence of reoxidation temperature firing on the PTCR effect of (1 x)BaTiO3–xNa0.5Bi0.5TiO3 ceramics was investigated. The effect of Na0.5Bi0.5TiO3 concentration on resistivity and microstructure of the reoxidized samples was investigated by means of complex impedance spectroscopy and scanning electron microscopy. It has been found that the grain size decreases with the increase in Na0.5Bi0.5TiO3 content. The values of minimum ρmin and maximum ρmax resistivities of the samples were observed to increase with the increase in reoxidation temperature in the 600 – 1000°C temperature range. It was shown that with increasing in reoxidation temperature of (1-x)BaTiO3-xNa0.5Bi0.5TiO3 solid solutions, potential barrier at grain boundaries increases.

The preparation of fine-grained positive temperature coefficient resistance with superior electrical properties

The electrical characteristics of positive temperature coefficient resistance (PTCR effects) mainly come from the grain boundary. The useful way to enhance electrical characteristics of PTC ceramics is to decrease the grain size and add the number of grain boundary. In the paper, the grain size and PTCR effects of ceramics were investigated on the effects of the molar ratio of donor and acceptor, the sintering process and high-energy ball milling. The formulation of prepared ceramics were Ba0.8Sr0.2Ti1.01O3+0.03mol% Mn(NO3)2+x mol Y2O3+2wt% SiO2. The grain size of these PTC ceramics was decreased to only [email protected] by adding Sr^2^+ and Y^3^+ to substitute the A-site barium ions, which were calcined at 1220^oC and sintered at 1300^oC after high-energy ball milling for powders. The prepared ceramics exhibited room temperature resistivity of [email protected], resistance rising rate more than 10^4unit through the Curie temperature, and relative density between 75% and 90%.

Phase transition and PTCR effect in erbium doped BT ceramics

Abstract In this work the dielectric behaviour and main features of the phase transition of BaTiO 3 and Ba 0.99 Er 0.01 TiO 3 ceramics were carefully investigated. The temperature and frequency dependences of the dielectric properties of erbium doped BaTiO 3 ceramics were measured in the 25–225 °C and 100 Hz to 10 MHz ranges, respectively. From this study, a dielectric anomaly in the ferroelectric–paraelectric phase transition of the Ba 0.99 Er 0.01 TiO 3 ceramic was observed. The features of the samples phase transition were analysed by using Curie–Weiss, Santos–Eiras’ and order parameter local phenomenological models. In the BaTiO 3 system, all models showed a normal phase transition, while was not possible to establish the character of the phase transition in the Ba 0.99 Er 0.01 TiO 3 system. The relaxation parameters of conductive processes for the study ferroelectric materials, analysed in the time domain, did not show any influence on the ferroelectric–paraelectric phase transition. Finally, it was demonstrated that the anomaly observed on the phase transition of the erbium doped BaTiO 3 ceramics is associated with the processes that results in the PTCR effect.

The Positive Temperature Coefficient of Resistivity Effect in (<i>1-x</i>)KNbO<sub>3</sub>-<i>x</i>BaGeO<sub>3</sub> Based Ceramics

(1-x)KNbO3-xBaGeO3 based PTCR ceramic materials are prepared using high purity K2CO3, Nb2O5, GeO2, Al2O3 and BaCO3 powders as starting materials, and the structural and electrical properties have been investigated. The results indicated that the samples doped with minute Ba as donor show excellent PTCR effect above the temperature of about 36°C. For the 0.40at% Ba-doped sample, the minimum resistance of 4.2×104Ω·cm, temperature coefficient (αk) of 24.37%/°C, PTCR anomaly lg(Rmax/Rmin) of 3.82 and transition temperature (Tmin) of 36°C are obtained.

The structure and PTCR effects of Mg-doped ZnTiO3 ceramics

Zinc titanate doped with magnesium was produced by a conventional solid state reaction technique using metal oxides. The X-ray powder diffraction pattern showed a single phase of ZnTiO3. The magnesium can replace the zinc ions and form a solid solution in the ZnTiO3 phase, and the intensities of the ZnTiO3 peaks decreased with increasing addition of Mg. The materials thus produced are semiconductors, with a positive temperature coefficient of resistivity. Increased addition of magnesium decreases the electrical resistivity. In addition, the sintered density and c/a ratio also rise with the increasing addition of Mg, while the open porosity decreases. Moreover, the Curie temperature (Tc) of the (Zn1−xMgx)TiO3 materials can be shifted to a higher temperature by increasing the Mg2+ concentration.