PTC Ceramics Research Articles

Extra high temperature coefficient in semiconducting BaTiO3-(Bi0.5Na0.5)TiO3-SrTiO3 ceramics

Sr is often doped on the Ba-site of ferroelectric perovskite BaTiO3-based PTC ceramics to move the Curie point of BaTiO3 from ~ 120 °C to a lower value for special applications. However, the addition of Sr often decreases their temperature coefficients. Although many methods were adopted to improve it, the temperature coefficient is still under 25%. In this paper, we introduced a small amount x of (Bi0.5Na0.5)TiO3 into BaTiO3-SrTiO3 PTC ceramics. As a result, the temperature coefficient of (1-x) (BaTiO3-SrTiO3)-x(Bi0.5Na0.5)TiO3 ceramics reached an extra high value ~ 38.3% at x = 0.02 and meanwhile its room temperature resistivity was still a practical value of ~ 555.7 Ω cm. The maximum temperature coefficient reached up to ~ 54.0% at x = 0.03 and the corresponding room temperature resistivity was ~ 4930.2 Ω cm. The shift of the Curie point caused by the addition of BNT can be easily offset because that its amount was small. The excellent temperature coefficient was attributed to the weakened relaxation behavior induced by addition of BNT.

Effect of Defect Characteristics on the Color of BaTiO<sub>3</sub>-Based PTC Ceramic

The barium titanium based PTC ceramic with two kind of colors, light blue and yellow, were obtained by changing sintering processing. In order to reveal the relationship between color and electrical properties of the ceramics. The phase structure and microstructure of as synthesized samples were investigated by powder X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. The micro area elements were characterized by electron probe micro-analyzer (EPMA) and x-ray photoelectron spectrometer (XPS). The thermo-sensitive properties were studied by resistance-temperature measurement system. The results reveal that two kinds of PTC ceramics have the same structure, similar elements, but different microstructure and valence concentration of titanium. It is suggested that difference of color of the PTC ceramics are originated from the defect concentration of titanium.

Modeling of electrical properties of grain boundaries in n-conducting barium titanate ceramics as a function of temperature and dc-bias

Abstract A double Schottky barrier model suitable for the description of the grain boundary resistivity of n-conducting BaTiO 3 ceramics has been modified by taking account of frozen-in diffusion profiles of cation vacancies at the grain boundaries which are formed during the cooling process after sintering. The space charge model has been extended in order to predict the electrical properties of PTC ceramics (positive temperature coefficient of resistivity) under voltage load for maximum dc-bias values around 0.3 – 0.5 V/grain boundary. The effect of the voltage drop across the Schottky barrier on the concentration profiles of electrons in the depletion zone as well as the space charge potential has been elaborated in detail.

A comparative study on positive temperature coefficient effect of BaTiO3–K0.5Bi0.5TiO3 ceramics by conventional and microwave sintering

Abstract As a promising material for lead-free positive temperature coefficient of resistivity (PTCR) ceramics, (1− x )BaTiO 3 – x K 0.5 Bi 0.5 TiO 3 ( x =0.002–0.008) samples were prepared by conventional sintering (CS) and microwave sintering (MS) techniques. The effects of different sintering method on the phase composition, microstructure and PTCR characteristics of the ceramics were investigated. The sintering cycle of ceramics was 2.5 h by MS, whereas it took 14 h by CS. Using the microwave heating, the sintering temperature to get high dense material is lowered by 40 °C compared to CS samples. The XRD results showed that all samples were pure tetragonal phases by both sintering process. Meanwhile, the MS samples had smaller grain size and uniform grain distribution. For PTC ceramics, MS was superior to CS due to rapid processing and uniform temperature distribution throughout the specimen. Thus, it exhibited improved PTC properties with lower room temperature resistivity ( ρ RT ), higher Curie temperature ( T c ) and steep resistance jump (lg( ρ max / ρ min )).

BaTiO3PTC 써미스터의 미세구조 및 전기적 특성에 대한 SiO2영향

PTCR ceramics of <TEX>$(Ba_{0.998}Sm_{0.002})TiO_3+0.001MnCO_3+xSiO_2$</TEX> (x=1, 2, 3, 4, 5, 6 mol%) were fabricated by solid state method. Disk samples of diameter 5 mm and thickness about 1mm were sintered at <TEX>$1,290^{\circ}C$</TEX> for 2 h in reduced atmosphere of <TEX>$5%H_2-95%N_2$</TEX> followed by re-oxidation at <TEX>$600^{\circ}C$</TEX> for 30 min. in <TEX>$20%O_2-80%N_2$</TEX>.and their microstructures and electrical properties were investigated with SEM and Multimeter. The color of sintered samples was strongly dependent on <TEX>$SiO_2$</TEX> content showing that the color of samples with <TEX>$SiO_2$</TEX> of 1~2 mol% was gray but that of samples with <TEX>$SiO_2$</TEX> of 4~6 mol% was changed from gray to blue, which seems to be related with the reduction of samples due to the oxygen vacancies created during the sintering in reduced atmosphere. <TEX>$SiO_2$</TEX> content had a great influence on the microstructure and the electrical properties. With increasing <TEX>$SiO_2$</TEX> content, the grain size of samples increased and the resistivity as well as the resistivity jump (<TEX>$R_{285}/R_{min}$</TEX>) decreased, which is considered to be attributed to the resistivity change at grain interior and grain boundary due to the fast mass transfer through <TEX>$SiO_2$</TEX> liquide phase during the sintering. Samples with 2 mol% <TEX>$SiO_2$</TEX> has the resistivity of <TEX>$202{\Omega}cm$</TEX> and the resistivity jump of 3.28. It is expected that <TEX>$SiO_2$</TEX> doped <TEX>$BaTiO_3$</TEX> based PTC ceramics can be used for multilayered PTC thermistor due to the resistance to the sintering in reduced atmosphere.

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%.

The Metallization of PTC Ceramic by Magnetron Sputtering

Abstract DC magnetron sputtering was applied in the deposition of the electrodes of the BaTiO 3 -based PTC ceramics. Multi-layered films of Ti/Ni-Cu/Ag and Al/Ni-Cu/Ag were prepared as the electrodes of PTCR ceramics. Experimental results indicated that there could form good ohmic contacts between BaTiO 3 -based PTC ceramics and the electrode materials. Also, the electrodes had good adhesion to the substrates and high-temperature welding characteristics. The proposed method has such advantages as economic consumption of production cost and controllable process, thus is suitable for large-scale industrial production.

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.

Preparation and characterisation of BaTiO3 based PTC ceramics with high performance

The nanocrystalline BaTiO3 based PTC powders had been prepared by a simple sol–gel method starting from comparatively cheap raw materials. The powders and ceramics were characterised by thermogravimetry–differential scanning calorimetry, X-ray diffraction and scanning electron microscopy, while electronic properties of the ceramics were also studied. The good material electronic properties were obtained, including a Curie temperature (TC) of 100°C, a resistivity at room temperature (ρ25°C) of 18 Ω cm, a high resistivity step ratio (ρmax/ρmin) of 1·2×106, a temperature coefficient of resistivity (α30) of 17% °C−1 and a withstand voltage intensity (Vb) of 196 V mm−1.

Microstructure and Electrical Properties of BaTiO&lt;sub&gt;3&lt;/sub&gt;-Based PTC Ceramics Prepared from Nanopowders

Dense PTC ceramics were prepared with BaTiO3 nanopowders synthesized by hydrothermal method. BaCO3 and Ti(OC4H9)4 were used as barium and titanium sources, and Y(NO)3·6H2O as the donor dopant respectively. The average grain size of the powders obtained after hydrothermal treatment at 160°C for 9h was about 30nm with cubic structure. Mn(NO3)2 was introduced to the as-prepared nanopowders in order to improve the PTC effect. After sintered at 1280°C, the PTC ceramic samples exhibited sufficient resistance jump ratio(1.086×103) around Curie temperature, the density of which was 5.81g/cm3(96.5% of the theoretical density).

Fabrication of BaTiO&lt;sub&gt;3&lt;/sub&gt;-Based Semiconducting Ceramic Thick Films by Aqueous Tape Casting

Semiconducting barium titanate powderss with an average particle size less than 40 nm were used for tape casting. Green tapes with a thickness of 100-500 μm were tape-cast from aqueous slurry of barium titanate powders using polyvinyl alcohol (PVA) as binder and polyelectrolyte ammonium salt as dispersant. The solid loading, viscosity and rheological properties of the ceramic slurries were investigated. Slurries with low viscosity were obtained when the concentration of dispersant was 1.5-2.0 wt% (based on ceramic powders weight) with fixed 75 wt% solid loading. The highest solid loading and optimum dispersion were determined through the proper viscosity to cast. Microstructure and PTC effect of the ceramic chips were studied as a function of firing temperature. Yttrium ions were homogeneously diffused into barium lattices at a low temperature of 1240 °C, and fine-grained PTC ceramics with grain size of 1-2 μm were developed successfully. These results can be explained by the higher rate of reactivity of finer powders and stable behavior of the suspension.

Electrical properties of Y- and Mn-doped BaTiO 3-based PTC ceramics

A series of nano-Ba 0.85− x Y x Sr 0.07Ca 0.08Mn y Ti 1− y O 3 (0.7% ≤ x ≤ 1.2%, 0% ≤ y ≤ 0.06%) solid solutions have been synthesized by solid-state reaction at low temperature. The experiment of doping different content Y and Mn shows that the room-temperature resistance decreases by doping Y, and the resistance jump increases dramatically by doping Mn. The optimum donor level increases significantly with increasing acceptor level. The room-temperature resistance changes as a U-type curve with an increase of Mn additive concentration while the resistance jump is on the reverse. Meanwhile, the influence of sintering temperature and soaking time on property of PTC materials was discussed.

Ni/Graphite/BaTiO&lt;sub&gt;3&lt;/sub&gt; PTCR Composites

Nickel/graphite/BaTiO3 PTC composites with lower room-temperature resistivity and higher resistance jump were fabricated by adding graphite and nickel powders into BaTiO3 PTC ceramics. Characteristics and conductive mechanism of the composites were discussed based on the experimental results.

Impedance Analysis Study on the Sensing Process of BaTiO&lt;sub&gt;3&lt;/sub&gt; Based PTC Ceramics in CO Gas

Impedance spectroscopy is suitable to evaluate the electric structure and behavior by probing the relaxational processes during the charge transport within this kind of electrically inhomogeneous PTCR ceramics. This technique has been used to characterize the change of structure and behavior in sensing process of La-doped PTC-type BaTiO3 as a CO gas sensor. The kinetic behavior of PTCR-CO ceramics in sensing process was detected. The sensitivity of the PTCR-CO comes from the change in the grain-boundary resistance of the ceramics with different temperatures in surrounding atmosphere. An important indirect evidence for the creation of new electron traps in grain boundaries of the semiconducting PTCR ceramics have been found using by impedance spectrum. And the creation of the new defects and electron traps in grain boundaries, [VO •], [e¢], and/or [Vo ×], still plays a dominate role.

Air-fired Ni for ohmic electrode of PTCR

The constitution and furing-technology of Ni paste were experimentally investigated. The experimental results show that the contact resistance could be lowered by adding glass powder and Boron powder, respectively used as adhesive and antioxidant when the content of Ni powder is higher than 65 wt%. By firing at 810 °C, Ni paste obtained could form a good ohmic contact to PTC ceramics, as shown by SEM iamges. In addition, we compared the electrical properties of PTCR ceramics measured with various electrodes and found that fired-Ni contact is superior to contacts made by fired-Al and sputtered-Ni.

PREPARING DOUBLE-BASE THERMO-SENSITIVE CERAMICS WITH NANOPOWDERS

The preparing process and the properties of thick-film double-based thermo-sensitive material were studied. The preparing steps were as follows: (i) preparing Ba 1-x Sr x TiO 3 micro-powders with chemical co-precipitation method; (ii) adding dispersants and surface active agents into crushing medium powders to prepare Ba 1-x Sr x TiO 3 nanopowders; (iii) preparing V 2 O 3-based micro-powders; (iv) mixing Ba 1-x Sr x TiO 3 nanopowders, V 2 O 3-based micro-powders, donor impurities, acceptor impurities and micro additives according to a certain ratio to make thick-film thermo-sensitive ceramic material. The presintering and sintering temperature of the prepared PTC ceramics were both reduced, which is very meaningful in using cheaper SiC instead of more expensive MoSi 2, prolonging the kiln's life, and lowering the production cost. The samples we prepared did not contain PbO , so they are safe to the environment.

住宅基礎コンクリートの冬期養生方法の開発(材料施工)

There was a problem of always securing prevention of an initial frost damage and prescribed strength in construction in winter of housing foundation concrete. PTC ceramics were developed as a new technology to solve the problem and the heater element heat curing seat industrial method was developed. It is a safe, reliable care method because PTC ceramics are the resistance bodies into which resistance sensitively changes depending on the temperature, and the ambient temperature is detected and it controls the calorific value automatically. It was confirmed that it was a concrete care method with effective this care method from the care performance examination result and the construction data compared with the method of taking care of one's health the heating of the past etc.

Grain Boundary Potential Barrier in Barium Titanate PTC Ceramics

Grain Boundary Potential Barrier in Barium Titanate PTC Ceramics

Mössbauer study of iron in V2O3-based PTC ceramics

Mössbauer study of iron in V2O3-based PTC ceramics

XPS study of (V0.995Al0.005)2O3 PTC ceramics

XPS study of (V0.995Al0.005)2O3 PTC ceramics