Nonstoichiometry and Ferroelectric Properties of PbNb2O6-Type Compounds

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Abstract
The crystal structure of PbNb2O6 consists of a framework of NbO6 octahedra linked through corners. The Pb2+ ions occupy 5 out of the 6 available interstitial sites in this framework. Single‐phase compositions have been prepared by solid‐state reactions to yield nonstoichiometric compounds of the form A1+xB2O6 where A and B may consist of two ions of different valency and x has values between —0.08 and 0.15. In these materials, the number of unfilled interstitial sites inherently present in PbNb2O6 lattice has been varied. Lattice parameter and x‐ray intensity data confirm that the additional ions introduced occupy the same sites as Pb2+ ions. The ferroelectric Curie temperature has been studied as a function of the composition of these dielectric solids. For compositions with x>0, the Curie temperature is not very sensitive to composition. As the number of unfilled interstitial sites increases (x<0), the Curie temperature decreases sharply.