Measurements of the dielectric constant, polarization, zero-field specific heat, and field-dependent specific heat of polycrystalline Pb2Nb2O7 at low temperatures are reported. No evidence for a phase transition at 15 K was found, contrary to previous suggestions of an antiferroelectric transition at 15 K based on dielectric data. The peak in the dielectric constant appears to be due to relaxation phenomena.
Properties of stacked SrTiO3/Al2O3 metal-insulator-metal capacitorsMeasurements of the temperature dependence of the dielectric constant and polarization in a constant field have been made on nominally pure SrTi0 3 ceramics and SrTi0 3 ceramics containing vanadium and niobium impurities. The peaks in the dielectric constant and the remanent polarization observed are apparently not due to a ferroelectric or antiferroelectric transition but rather to the presence of a thermoelectret state existing for permanent dipoles in the materials. It is suggested that the permanent dipoles have an origin similar to the impurity-vacancy dipoles found in alkali halides. PACS numbers: 77.30.+d, 77.40.+i, 77.80.Bh. 77.20.+y The specimens were mounted on a thermally isolated block inside a vacuum can immersed in liquid helium.
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