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Measurements of the dielectric constant κ in high-purity BaTiO3 ceramics as a function of temperature show that κ is quite dependent on grain size in the ferroelectric state while it is almost independent of grain size in the paraelectric state. In the ferroelectric orthorhombic and rhombohedral phases, κ decreases rapidly with lowering temperature when grain size is reduced smaller than 3 μm. It is also observed that the Curie temperature Tc is decreased very slightly, but the lower two transition points are shifted to higher temperatures as grain size decreases.

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Measurement of the Hall coe%cient in the Ba2Yl -Pr"Cu307-& system has revealed that an increase in Pr concentration reduces the Hall carrier number (1/eRH) and its strong temperature dependence. The Cu formal valence calculated from the Pr valence, which has been determined to be -+3. 5, shows a weakly decreasing dependence on Pr concentration. T, shows a stronger dependence on the Hall carrier number and the Cu-0 formal valence than in the oxygen-depleted Ba2YCu307-g system. The persistence of the chain band explains this observed difference, suggesting that the actual Cu-0 valence dependence of the 90-K superconductor is stronger than that of the 40-K superconductor.Of known Ba2[lanthanide]Cu307s compounds, only the Pr compound shows neither superconductivity nor metallic conduction, although it has an orthorhombic structure isomorphic to that of Ba2YCu307 (Refs. 1 and 2). Thus, the difference in the electronic and/or the crystal structure between these compounds might be a key parameter controlling superconductivity as well as normalstate properties of the high-T, copper oxides. It is known that a series of single-phase Ba2Y1-"Pr"Cu307-s can be synthesized. 34 They continuously range from superconductors to insulators. It is generally accepted that in high-T, copper oxides, the total carrier density is a crucial parameter by which the conduction properties are determined.There are several systems, for example,

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