'Tuning the electrical properties of B-site d0 perovskites as energetic chameleons: from ‘fast ion’ conduction to ‘weakly coupled relaxor ferroelectrics’

Abstract: Ferroelectricity is a common phenomenon in (d^o) titanate-based perovskites such as BaTiO₃, (Na_1/2Bi_1/2)TiO₃ and Pb(Zr,Ti)O₃. These materials are commercially important electroceramics with applications as high permittivity dielectrics and piezoelectrics in multi-layer ceramic capacitor (MLCC) and/or actuators: over 3 Trillion BaTiO₃-based MLCC’s were produced last year. To improve their performance and develop new applications requires manipulation of their structure-composition-property relationships. For example, by creating changes in stoichiometry, formation of solid solutions with other (often high pressure) perovskites and developing inter- and intra-granular segregation of dopants. We illustrate some of these mechanisms and changes in functional properties using the following three example systems to exemplify some of the ‘chameleon’ characteristics of perovskite oxides:

(i) (Na_1/2Bi_1/2)TiO₃: remarkably small changes in the A-site Na,Bi content can transform this dielectric material into an unexpected and excellent oxide-ion conductor and donor and/or acceptor-doping of the lattice can be used to control the level of defects and therefore ‘tune’ the electrical properties from oxide-ion conduction (type I) via mixed ionic-electronic conduction (type II) to polar dielectric behaviour (type III).

(ii) (BaTiO₃)_1-x-(BiScO₃)_x: forming a solid solution between these two perovskites can transform a classic ferroelectric (BaTiO₃) with very temperature dependent permittivity behaviour into a weakly coupled relaxor ferroelectric with high permittivity (~ 1000) over a remarkably wide temperature range (~ 100 – 400 ^oC).

(iii) Na_1-3xBi_xNbO₃: partial replacement of Na⁺ by Bi³⁺ with the creation of A-site vacancies in NaNbO₃ can induce intrinsic clustering of lattice distortions that leads to displacive order–disorder behaviour with increasing x. This remarkable solid solution initially exhibits interesting polar dielectric phenomena such as anti-ferroelectricty (x =0.00) and relaxor ferroelectricity (x =0.10) before undergoing an order-disorder transition that promotes co-existence of weakly coupled relaxor ferroelectricity and Na⁺ ion conduction (x =0.20).

Biography: Derek is a Professor in Materials Chemistry at the Department of Materials Science and Engineering at the University of Sheffield. He has particular expertise in relating defects in functional oxides to properties, chemistry, and synthesis, through the use of a range of structural and electrical characterisation techniques.

Everyone is welcome to attend, and if anyone wishes to meet with Derek then please get in touch with struan.simpson@warwick.ac.uk.