The dielectric constant of monoclinic zirconia and of lime-zirconia (up to a CaO content of 20% mole) has been measured at 25 °C by the powder method. For pure Z r02 the D.C. is 13.5, while for lime-zirconia a non linear dependence on the CaO content has been observed in the measured range, with a maximum at about 14% mole CaO. The results are discussed, in the light of the authors previous density data for the same systems, in terms of the width of the homo geneity range of the solid solutions. In tro d u c tio nThus, the questions of the dielectric constant of A large scattering exists within the literature values of the dielectric constant of pure Z r0 2 (11 < e < 2 8 ), measurements having been made mostly on thermal or anodic films and only in very few cases on bulk material. In particular, H a r r o p and Wanklyn 1 gave a value of 22 + 3 obtained on little single crystals 2, while C ox 3 reported a value of 11 + 1 for thermal and anodic films. Such strong discrepancies might be accounted for, among other factors, by the influence of the morphology of the samples and of the experimental methods, as it was recognized by the same authors 1> 3.As for lime-zirconia, K r ö g e r 4 quoted a value of 12.5, while emphasizing that the dielectric constant of such system had not been systematically investi gated as a function of lime concentration. From data reported by H a r r o p and W a n k l y n 1 on calcia-and magnesia-stabilized zirconia, it might be inferred that the dielectric constant in these cases is practically insensitive to quite large changes in com position. This would be somewhat surprising, if one considers, e. g., that V a n V e s s e m 5 showed the di electric constants of NaCl + NaBr and KJ + KBr solid solutions to be strongly in excess over the additive values. pure zirconia and of lime-zirconia are still open to further investigation. The latter presents some in teresting theoretical connections with the defect solid state of solid solutions or, at least, with the equi librium phase diagram of the system Z r0 2 -CaO. Moreover, to our knowledge, no other research has been carried out after that of Van Vessem on the dielectric constant of solid solutions of ionic solids.In this paper, the results of dielectric constant measurements, by the powder method, on pure Z r0 2 and some Z r0 2 + CaO solid solutions in the com position range 8 -f-20 mole % CaO are reported. Although the powder method suffers from a largely approxim ate theoretical treatment, it turns out con venient since it allows the use of finely ground pow ders instead of large and flat slabs of single crystals or large size pressed pellets, being at the same time free from the errors involved in the film method.T h e P o w d e r M ethod By this method one determines the apparent di electric constant of the heterogeneous system form ed with the investigated solid, in powdered form, and a gaseous phase (or the vacuum ). The pre-