title: Towards novel multiferroic and magnetoelectric materials: dipole stability in tetragonal tungsten bronzes.
abstract: We discuss the strategy for development of novel functional materials with the tetragonal tungsten bronze structure. From the starting composition Ba6GaNb9O30, the effect of A- and B-site substitutions on the dielectric properties is used to develop an understanding of the origin and stability of the dipolar response in these compounds. Both tetragonal strain induced by large B-site cations and local strain variations created by isovalent A-site substitutions enhance dipole stability but result in a dilute, weakly correlated dipolar response and canonical relaxor behaviour. Decreasing cation size at the perovskite A2-site increases the dipolar displacements in the surrounding octahedra, but insufficiently to result in dipole ordering. Mechanisms introducing small A-site lanthanide cations and incorporation of A-site vacancies to induce ferroelectricity and magnetism are presented.
authors.affiliation: EaStCHEM School of Chemistry, University of St Andrews, , North Haugh, St Andrews, Fife KY16 9ST, UK.
authors.forename: Andrei
authors.initials: A
authors.lastname: Rotaru
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Miller
authors.forename: Donna C
authors.initials: DC
authors.lastname: Arnold
authors.forename: Finlay D
authors.initials: FD
authors.lastname: Morrison
keywords: dielectric properties; ferroelectric; multiferroic; relaxor; structure–property relationships