The effect of adding 0.05 to 16.2 mol.% CeO2 on the dielectric properties and loss tangent of sintered BaTiO3 was investigated at different temperatures. The permittivity increased with CeO2 additions up to 0.5 mol%, then decreased with increasing concentrations. In the samples doped with 5.6 and 16.2 mol.% CeO2 the curves show a slight increase in the permittivity with temperature, without any significant tendency to a peak value, down to room temperature. Smaller additions of CeO2 (0.05 to 2 mol.%) lower the Curie temperature to 92 degrees C. The loss tangent maximum (tan delta )max at the Curie temperature was less than 0.035 for pure BaTiO3 and 0.0120 for samples containing 16.2 mol.% CeO2. X-ray measurement shows that the lattice parameters change with the concentration of additive, the a axis expanded while the c axis shrank, approaching a cubic structure at room temperature for 5.6 mol.% CeO2(c/a=1.001249). Shrinking of the c axis reached its maximum at 16.2 mol.% CeO2 (c/a=0.994341).

The dielectric constant (E) and the loss tangent (tan 6) of barium titanate doped with ytterbium oxide with different concentrations (0 to 6 mol%), were investigated at different temperatures. The peak value at the transition temperature of both E and tan 6 continuously decreased with increasing dopant concentration and the ferroelectric behavior disappeared in the samples with a Ybz03 concentration of 6 mol%. The X-ray diffraction studies showed that the group of lines (103) of BaTi03 coalesced in one broad line at a concentration of 6 mol% Ybz03 and the structure changed from tetragonal to cubic at room temperature. Micrographs taken by SEM showed a continuous decrease in the grain size of BaTi03 on increasing the Yb concentration. On adding 6 mol% Yb203, the grain size decreased from 25.7 to 1.9 pm and the matrix became fine-grained, with no significant domain pattern.

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The permittivity of BaTiO3 doped with small concentrations of Gd2O3 (0.01 approximately 0.1 mol.%) are found to be remarkably dependent on the type of the solid solution formed between Gd2O3 and BaTiO3. The decrease of permittivity at the Curie peak with decreasing grain size for BaTiO3 doped with concentrations of Gd2O3 from 0.5 approximately 3 mol.% is attributed to the formation of defective non-ferroelectric grain boundary layers of low permittivity.

shows a single isotropic electron spin resonance line a t g = 2.011. The resonance is attributed t o conduction electron spin resonance of colloidal, small-size, sodium metal clusters. The process of aggregation of sodium and the general behaviour of the isotropic line are discussed with reference to some of the postulated mechanisms.Blaues Sodalit Na,(Al,Si,O,,)Cl, zeigt eine isolierte isotrope Elektronenspinresonanzlinie bei g = 2,011. Die Resonanz wird der Leitungselektronen-Spinresonanz von kleinen kolloidalen Natriummetallclustern zugeordnet. Der AggregationsprozeB von Natrium und das allgemeine Verhalten der isotropen Linie werden beziiglich einiger der postulierten Mechanismen diskutiert.