Dielectric Properties of the Lamellar Niobates and Titanoniobates AM₂Nb₃O₁₀ and ATiNbO₅ (A = H, K, M = Ca, Pb), and Their Condensation Products Ca₄Nb₆O₁₉ and Ti₂Nb₂O₉

The dielectric properties of layer perovskites in the Dion−Jacobson (KCa 2 Nb 3 O 10, HCa 2 Nb 3 O 10, CsPb 2 Nb 3 O 10, HPb 2 Nb 3 O 10, KCa 2 NaNb 4 O 13, KLa 2 NbTi 2 O 10 ) and Ruddlesden−Poppper (K 2 La 2 Ti 3 O 10 ) series, and of related lamellar oxides (KTiNbO 5, HTiNbO 5 ) 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 HPb 2 Nb 3 O 10, however, is ∼150 between 1 kHz and 10 MHz, and its dielectric loss is <0.1 over the same range. Topochemical dehydration of HTiNbO 5 to Ti 2 Nb 2 O 9 eliminates the loss components associated with intra- and intergrain proton movement. HCa 2 Nb 3 O 10 undergoes a similar topochemical dehydration reaction to make a new metastable phase, Ca 4 Nb 6 O 19, for which a structural model is proposed. Above 550 °C, Ca 4 Nb 6 O 19 decomposes to a mixture of microcrystalline CaNb 2 O 6 and Ca 2 Nb 2 O 7 . Unlike HCa 2 Nb 3 O 10, HPb 2 Nb 3 O 10 does not dehydrate topochemically, but transforms directly to a mixture of Pb 3 Nb 4 O 13 and PbNb 2 O 6 .