W. Jakubowski

Studies on preparation and electrical conductivity of BICOVOX

Abstract A member of the BIMEVOX family with vanadium partially substituted by cobalt (Bi 2 Co 0.1 V 0.9 O 5.35 -BICOVOX.1) was synthesized. The synthesis process was investigated by means of DTA. Dense ceramic samples were obtained after several minutes of sintering at 850°C, which is a higher temperature than that required for BICUVOX.1 (800°C). The Arrhenius plots of the total electrical conductivity for the obtained samples consist of two straight line sections with distinctly different values of activation energy. Between 400 and 500°C a rapid increase of conductivity with increasing temperature is observed. At temperatures above 500°C the conductivity of BICOVOX.1 is slightly higher than that of BICUVOX.1. Except for the first heating, the conductivity values during heating and cooling cycles are approximately the same.

Transition from ionic to electronic conduction in silver–vanadate–phosphate glasses

A series of silver-vanadate-phosphate glasses of the AgI-Ag 2 O-V 2 O 5 -P 2 O 5 system has been prepared and their electrical properties have been studied. Compositions of high AgI content and low V 2 O 5 content exhibited pure ionic conduction. On the other hand, vanadium-rich and silver-poor glasses were almost pure electronic conductors, for which, depending on temperature, the models of phonon-assisted hopping of small polarons or variable range hopping can be applied. Samples of intermediate compositions exhibited mixed ionic-electronic conductivity. The observed transition from ionic- to electronic-type conduction in the frame of the same system could be of interest for possible practical applications, e.g. in integrated microbatteries.

Influence of preparation procedure on some physical properties of BICUVOX

Abstract The influence of preparation conditions on some physical properties of BICUVOX.10 (Bi 2 V 0.90 Cu 0.10 O 5.35 ) is reported. Differential thermal and X-ray analyses indicate that synthesis of the compound can be accomplished at 610 °C. The densification characteristics show that high density BICUVOX ceramic can be obtained after several minutes of sintering at 800 °C. The electrical conductivity was studied by a.c. impedance methods. Separation of the contributions of grain interiors and grain boundaries to the total resistance was possible at temperatures below around 350 °C. The Arrhenius plots of the total conductivity consist of two straight line sections with a change in slope at around 500 °C. The activation energy was about 0.48 eV at high temperatures for all the samples. Below around 500 °C the activation energy was in the range from 0.62 to 0.72 eV depending on the preparation procedure. Lower values of activation energy and higher values of conductivity were obtained for well-sintered samples, which is related to the smaller contribution of the grain boundaries to the total electrical resistance of a sample.

Electrical properties of AgI–Ag2O–V2O5–P2O5 glasses

Abstract Mixed conductive silver vanadate–phosphate glasses were prepared and their electrical properties were studied. Compositions of the glasses were characterized by parameters: x (AgI content) and r =[Ag 2 O]/[V 2 O 5 +P 2 O 5 ]. Total conductivity σ t ( x , r =constant) of a series of samples with fixed r values exhibited minima when plotted vs. x . The conductivity minima were accompanied by maxima of apparent activation energy E t ( x , r =constant). The observed dependencies were attributed to the ion–polaron effect (IPE), i.e. to electrostatic attraction between mobile species: electrons (polarons) and Ag + ions.

Some properties of mixed electronic-ionic glassy conductors of the AgIAg2OV2O5P2O5 system

Abstract The mixed electronic-ionic conducting glasses of the AgIAg2OV2O5P2O5 system have been prepared. XRD and DTA analyses have confirmed the amorphous nature of these glasses. DTA analysis was used to determine glass transition and recrystallization temperatures. EPR measurements showed that at the V2O5-rich end of the compositions, the number of V4+ ions, essential for electronic conduction, is considerable. Electrical properties have been studied using complex immittance spectroscopy. Numerical analysis of the admittance spectra showed that the ionic transference number at the AgI-rich end of the compositions is close to one and for the compositions with high V2O5 content it is considerably lower.

Bulk and grain boundary electrical conductivities of NASICON

Abstract The ionic conductivity of ceramic samples of NASICON was investigated by the use of the complex admittance method. Measurements were made in the frequency range 5−5×10 5 Hz from room termparature (RT) up to 400°C. The existence of three activation energies for both the bulk and the grain boundary conductivities is reported. A diffusive Warburg-like behaviour of electrical conductivity was revealed at temperatures where the value of the bulk conductivity approaches that of the grain boundary.

On some properties of NASICON doped with MgO and CoO

Abstract The influence of MgO or CoO doping on the chemical composition and on the electrical conductivity of NASICON ceramics was studied. It was found that the grain and intergrain electrical conductivities behave differently as a function of doping rate and the kind of dopant.

Effect of selected mobile ions on moisture uptake by beta″ alumina

Abstract The effect of mobile Na+, Ag+ and Li+ ions on water uptake of lithia stabilized beta″ alumina ceramics was investigated. The extent of water uptake was deduced from ionic a.c. conductivity, TGA and DTA measurements done on “moist” samples. It was found that contact with humid air influences electrical properties of bulk and grain boundary regions of Na+ beta″ alumina. The most influenced was Li+ Na+ beta″ alumina, the least Ag+ beta″. The TGA/DTA data are in good agreement with the electrical results.

Influence of doping on some physical properties of NASICON

Abstract NASICON samples were intentionally doped with Cu 2+ , Co 2+ and/or Zn 2+ ions. It is assumed that they substitute the Zr 4+ ions because of nearly the same ionic radii. The doping influences mostly the physical properties /electrical and mechanical/ of the grain boundaries but small alteration of the bulk electrical conductivity is also visible. The improvement of the mechanical properties of the NASICON samples under doping seems to be promising.

Electrical properties of glasses of the Na2OV2O5P2O5 system

Abstract Three series of glasses of the Na2OV2O5P2O5 system corresponding to different V2O5:P2O5 ratios have been prepared and their electrical properties have been studied. Each series consisted of samples of various sodium contents. It has been found that materials of compositions xNa2O·(1−x)(0.7V2O5·0.3P2O5) and xNa2O·(1−x)(0.6V2O5·0.4P2 O5) are predominantly electronic conductors. Activation energies for both series increase from 0.46 eV to 1.0 eV on increasing sodium content. The electrical conductivity at 300°C for the same range of x decreases from 1.2×10-3 S/cm (for x=0) to 1×10-4 S/cm (for x=0.5). The glasses with the lowest V2O5:P2O5 ratio (4:6) (a series xNa2O·(1−x)(0.4V2O5·0.6P2O5) for 0.3 ⩽ x⩽0.5) exhibit mixed electronic-ionic conductivity. Activation energies for that series are in the 0.7–0.8 eV range.