Dielectric Properties of the Lamellar Niobates and Titanoniobates

The dielectric properties of layer perovskites in the Dion-Jacobson (KCa2Nb3O10, HCa2Nb3O10, CsPb2Nb3O10, HPb2Nb3O10, KCa2NaNb4O13, KLa2NbTi2O10) and Ruddlesden-Poppper (K2La2Ti3O10) series, and of related lamellar oxides (KTiNbO5, HTiNbO5) were measured. Most of these compounds show significant dielectric dispersion and high loss, which are attributed to both grain and grain boundary atomic displacements. The dielectric constant of HPb2Nb3O10, however, is ∼150 between 1 kHz and 10 MHz, and its dielectric loss is <0.1 over the same range. Topochemical dehydration of HTiNbO5 to Ti2Nb2O9 eliminates the loss components associated with intraand intergrain proton movement. HCa2Nb3O10 undergoes a similar topochemical dehydration reaction to make a new metastable phase, Ca4Nb6O19, for which a structural model is proposed. Above 550 °C, Ca4Nb6O19 decomposes to a mixture of microcrystalline CaNb2O6 and Ca2Nb2O7. Unlike HCa2Nb3O10, HPb2Nb3O10 does not dehydrate topochemically, but transforms directly to a mixture of Pb3Nb4O13 and PbNb2O6.