Multilayer thick-film structures based on spinel ceramics

Temperature-sensitive thick films based on spinel-type semiconducting ceramics of different chemical composition Cu0.1Ni0.1Co1.6Mn1.2O4 (with p+-types of electrical conductivity), Cu0.1Ni0.8Co0.2Mn1.9O4 (with p-types of electrical conductivity), and their multilayers of p+-p and p-p+-p structures were fabricated and studied. These thick-film elements possess good electrophysical characteristics before and after long-term ageing test at 170 °C. It is shown that degradation processes connected with diffusion of metallic Ag into grain boundaries occur in one-layer p- and p+-conductive thick films. The p+-p structures were of high stability, the relative electrical drift being no more than 1%. Positron trapping processes in so-called “free” thick-film structures based on spinel-type Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics are studied. It is shown that two-state positron trapping model is appropriate for an adequate description of changes caused by additional glass phase in these materials. The observed behaviour of defect-related component in the fit of the experimentally measured positron lifetime spectra for thick films in comparison with bulk ceramics testifies in favour of agglomeration of free volume entities during technological process.

Study of Nonlinear Current-Voltage Characteristic of Semiconductor Ceramic by the Method of Tilted Energy Band

A analytic method for the calculation of the electrical characteristics of semiconducting ceramics is suggested. This paper put forward the concept of effective carrier concentration. Electrical characteristics under extra electric field have been calculated by the method of tilted energy band. The non-linear current-voltage characteristics with different grain sizes has been obtained. The results pointed out that the current-voltage characteristics divide into three regions: Linear region before breakdown field, nonlinear region near breakdown field and upturn region after breakdown field; The grain boundary barrier leads to the strong non-linear characteristics, which has nothing to do with the grain size. With the grain size decreasing, the breakdown field increases. The results are compared with experimental data.

Processing and characterization of CaTiO3 perovskite ceramics

Calcium titanate (CaTiO3) ceramics with perovskite structure were produced by solid state reaction. Calcium carbonate (CaCO3) and titanium dioxide (TiO2) were mixed (in molar ratios 1/1 and 3/2), and the obtained mixtures were calcined at 1150 ?C in successive thermal cycles. The obtained samples were characterized by differential thermal analysis, thermogravimetry, X-ray diffraction, measurement of particle size distribution and linear thermal shrinkage. XRD results indicated that the samples have perovskite CaTiO3 structure with small amount of secondary CaO and TiO2 phases, and their phase composition depends on the heat treatment conditions. The measured values of electrical resistivity were within the characteristic range of insulating materials and approach values corresponding to semiconducting ceramics.

Integrated Thick-Film P-i-p+ Structures Based on Spinel Ceramics

Multilayered temperature/humidity sensitive thick-film p-i-p+ structures based on spinel-type semiconducting ceramics of different chemical composition Cu0.1Ni0.1Co1.6Mn1.2O4 (with p+-type of electrical conductivity), Cu0.1Ni0.8Co0.2Mn1.9O4 (with p-type of electrical conductivity) and magnesium aluminate i-type MgAl2O4 ceramics, as well as p-p+ and p-p+-p structures were fabricated and studied. Temperature-sensitive thick-film structures possess good electrophysical characteristics before and after long-term ageing test at 170 оС, the relative electrical drift being no more than 1 %. Increase of number of thick-film layers from two to three results in the improvement temperature sensitivity of thick-film structures. It is shown, that just prepared humidity-sensitive thick films in one-layered performance posses good linear dependence of electrical resistance from relative humidity without hysteresis in the range of 40-99 %. Losses of the sensitivity of these elements in time at the normal physical condition are connected with degradation process on contact area. The integrated spinel-type p-i-p+ thick-film structures show humidity-sensitivity within one-order change of electrical resistance and are stable in time. These structures are shown to be successfully applied for integrated environmental sensors.

Fabrication of Lead-Free Semiconducting Ceramics Using BaTiO3-(Bi1/2Na1/2)TiO3 System by Sintering in Air Atmosphere

BaTiO3–(Bi1/2Na1/2)TiO3(abbreviated as BT-BNT) solid solution ceramics, as a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor material usable over 130°C, were synthesized in air atmosphere. By conventional processes, La-doping was not effective in giving semiconducting property to the BT-BNT ceramics because of volatilization of sodium and bismuth during sintering. By preventing the volatilization by lowering the sintering temperature using very fine TiO2powder and by adding calcium oxide to calcined BT-BNT powders, we obtained BT-BNT semiconducting ceramics which shows a resistivity change near Curie temperature.

Characterization of Grain Boundaries of Lead-Free Semiconducting Ceramics Using BaTiO3-(Bi1/2K1/2)TiO3 System

BaTiO3–(Bi1/2K1/2)TiO3 (abbreviated as BT-BKT) solid solution ceramics, as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C, has been synthesized by sintering in N2 atmosphere and after annealing in air over 1200°C. In the BT-BKT ceramics with PTC property, the impedance/modulus spectroscopic plots have revealed that a third resistance-capacitance (RC) response besides grains and grain boundaries. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers in the BT-BKT semiconducting ceramics.