Temperature Coefficient Of Resistivity Characteristics Research Articles

Preparation of porous (Ba,Sr)TiO3 by adding corn-starch

A new method of preparing porous (Ba,Sr)TiO3 ceramics has been introduced, using an ordinary ceramics processing technique. The effect of corn-starch on the positive temperature coefficient of resistivity characteristics and microstructure of the porous (Ba,Sr)TiO3 ceramics has been investigated. When the corn-starch addition was 1–20wt%, the PTCR jump was over 106 and 1–2 orders higher than that of samples without corn-starch. Also, it was found that the (Ba,Sr)TiO3 ceramics had porous microstructure by the addition of corn-starch. The porosity of the ceramics with 20wt% corn-starch was 44%. The electrical properties of the (Ba,Sr)TiO3 ceramics have been discussed, based on the microstructure, resistivity of grain boundaries, donor concentration of grains and the electrical potential barrier of grain boundaries.

Electrical properties of the positive temperature coefficient of resistivity materials with 490 °C critical temperature

This work successfully obtains a positive temperature coefficient of resistivity characteristics with critical temperature (Tc) at around 490 and 420 °C for PbTiO3 (PT), and (Pb0.9Sr0.1)TiO3 (PST) materials, respectively. The tetragonality of these materials are (c/a)PT=1.065 and (c/a)PST=1.046. In addition, the donor level of Y3+ ions in PT materials [(Ed)PT=0.09–0.11 eV] is smaller than that in PST materials [i.e., (Ed)PST=0.29–0.40 eV]. The resistivity jumping ratios of the two materials are similar, that is, (ρmax/ρmin)PT≅102.2 and (ρmax/ρmin)PST≅101.6. Multiple-Tc resistivity-temperature (ρ-T) characteristics are observed, that is ascribed to the formation of an incomplete core-shell microstructure with the Pb-deficient shell not entirely surrounding the stoichiometric core.

A Novel Method for the Uniform Incorporation of Grain‐Boundary Layer Modifiers in Positive Temperature Coefficient of Resistivity Barium Titanate

The presently developed two‐stage process involves diping the prefired porous disks of n‐BaTiO3 in nonaqueous solutions containing Al‐buty rate, Ti‐isopropoxide, and tetraethyl silicate and subsequent sintering. This leads to uniform distribution of the grain‐boundary layer (GBL) modifiers (Al2O3+ TiO2+ SiO2) and better control of the grain size as well as the positive temperature coefficient of resistivity characteristics. The technique is particularly suited for GBL modifiers in low concentrations (< 1%).

The effect of Mn on the positive temperature coefficient of resistance characteristics of donor doped BaTiO3 ceramics

BaTiO3 positive temperature coefficient of resistance (PTCR) specimens were made from commercial BaTiO3 which was mixed with 0.35 mol. % of Ho2O3 to make it semiconducting and 0.07 mol. % of MnCO3. After sintering at 1320 °C the samples were annealed in batches at 1220 °C for various periods between 0 and 5 h. The effect of Mn was studied by making direct comparison with previous results obtained from Mn free but otherwise identical specimens. Room-temperature dielectric measurements in the audio and radio frequency ranges revealed that Mn had a negligible effect on the grain bulk resistance. Mn was found to result in an increase in the minimum and maximum values of the resistivity, the temperature at which the resistivity is a maximum and the slope of the resistivity-temperature characteristic in the transition region, all of which were attributed to an enhancement of the potential barrier at the grain boundaries. The acceptor state energy of the Mn-doped samples was found to be ∼1.4 eV, while a lower value was obtained for Mn-free material (∼1.12 eV). The effective concentration of Mn acceptors was observed to increase with the annealing time. To explain this behavior a thin Mn-rich boundary layer was assumed to exist, within which there was partial compensation of the Mn ions due to the formation of ionized oxygen vacancies. During annealing in air at 1220 °C, oxidation takes place and more of these vacancies are filled resulting in an increase in the effective Mn concentration. This model is also capable of explaining other phenomena such as the disappearance of the PTCR effect in reduced samples and the effects of cooling rate and quenching on the PTCR behavior.

Industrial Sapphire - A Key to Reliable Microelectronics

The reliability of evaporated thin films of nichrome 1OO to 2,000 angstroms in thickness when deposited onto a ceramic substrate can be related to the physical and electrical properties of the substrate. Through careful selection of materials that are physically and electrically compatible with these extremely thin films, reliability and volumetric efficiency of precision film resistors can be materially improved. Evaluation of commercially available substrate materials resulted in the selection of industrial sapphire as a most superior substrate material. Reliability was improved by one order of magnitude, and volumetric efficiency was increased by a factor of thirty. The evaporated metal film deposited on monocrystalline industrial sapphire exhibited a marked uniformity of characteristics within the lot, as well as between lots of precision film resistors. Temperature coefficient of resistance, voltage coefficient and noise factor characteristics for evaporated nichrome sapphire resistors were found to be superior over alkaline earth and high alumina ceramic precision film resistors produced under identical evaporation conditions. Because of the excellent thermal conductivity of industrial sapphire, electrical ratings ranging between 1/2 watt at 25°C through 1/20 watt at 125°C were achieved for cylindrical resistor rods O.105" long x .050" diameter as compared to MIL-R-10509 resistor styles with rectilinear envelopes four times larger. The industrial sapphire precision film resistors achieve remarkable miniaturization, economical advantages through higher production yields, reduced temperature coefficient of resistance characteristics and substantially greater reli- ability.