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The positron annihilation lifetime spectra and their temperature dependence for the YBa2Cu3Oy superconducting ceramics doped with Sn have been studied. The results of analyses indicate that the element Sn is substituted for Cu(1) sites, and this leads to the ordering of the oxygen atoms as well as the increase of local electronic density in the Cu(1)-O layer where Cu(1) is substituted by Sn.

The superconductivity of YBa2Cu3Oy ceramics doped with SnO2 was studied. The superconducting transition temperature Tc was increased slightly as the SnO2 content changed from 0 to 5 wt.%. The results of the Mossbauer effect and the positron annihilation spectra showed that the Sn ions did substitute for Cu(1) sites. The increase in Tc may be attributed to the optimal carrier concentration as well as to the fine and dense microstructure obtained by doping with SnO2.

Perovskite-type La 1− x Sr x FeO3 (0⩽ x ⩽0.7) electronic ceramics are synthesized in an oxygen atmosphere using the solid phase reaction method. The resistance versus relative humidity (r.h.) characteristics as well as the dielectric and complex impedance spectra are investigated. The results indicate that the charge carriers are ions and electrons. The resistance of LaFeO 3 decreases with increasing r.h.; however, that of La 1− x Sr x FeO 3 (0.1⩽ x ⩽0.4) increases with increasing r.h. and its sensitivity increases with increasing x value. The experimental results are treated by a non-Debye model, and the equivalent circuit parameters are calculated. The model separates the samples into three regions: crystal grain, grain surface and electrode surface. The electrode surface resistance R e decreases with increasing r.h., but the grain resistance R g is not affected by water vapour. Whether the resistance—humidity characteristic is negative or positive is mainly determined by the crystal surface resistance R gs . R gs of LaFeO 3 decreases with increasing r.h., while R gs of La 1− x Sr x FeO 3 increases with increasing r.h.

A cadmium-antimony-oxide semiconductor ceramic synthesized by heating CdO and Sb/sub 2/O/sub 5/ is discussed. Its composition, structure, phase transition, and electrical properties have been systematically studied. The study indicates that the material is an n-type semiconductor, Cd/sub 6/Sb/sub 2/O/sub 10/. A reversible structural phase transformation occurs at about 240 degrees C. The transition temperature of the heating and cooling processes are 246 degrees C and 228 degrees C, respectively. The R-T curves can be divided into three temperature regions. The conduction mechanism in the three regions and the associated defect structure and phase transformation properties are discussed. The activation energy and carrier mobilities are calculated. >

The synthesizing process and mass transport mechanism of CdO-Sb2O5 ceramics are discussed. Two compounds with stable structure have been obtained and the crystal structures and microstructures are examined by XRD and SEM. A differential scanning calorimeter is used to determine the phase transformation and latent heat. The defect structure of these semiconducting ceramics are investigated by varying the atmosphere, trivalent ion doping, and Seebeck effect experiments.