Structure and properties of Bi2Ti2O7 pyrochlore type phase stabilized by lithium

• Published in: Journal of alloys and compounds 2018-01, Vol.732, p.178-186
• Main Authors: Lelievre, Jerome, Marchet, Pascal
• Format: Article
• Language: English
• Subjects: Dielectric response; Ionic conduction; Li2O-Bi2O3-TiO2 phase-diagram; Neutron diffraction; Pyrochlore; Solid state reaction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.10.128

A study of the Li2O - Bi2O3 - TiO2 ternary system evidenced a Bi2Ti2O7 pyrochlore phase in a large range of composition, centered on (Li1/2Bi1/2)TiO3 (LBT). This composition led to a pyrochlore phase stable up to 1100 °C, while pure Bi2Ti2O7 phase has been reported as metastable, with decomposition temperature around 600 °C. According to previous studies, this pyrochlore phase was not obtained without lithium and here only a few percent of lithium was necessary for stabilization. The structural study, performed by neutron diffraction, evidenced a cubic Fd3¯m structure (a = 10.317 Å), similar to the one of “pure” Bi2Ti2O7 pyrochlore phase. The Li-ion is probably located on the Bi-site and is responsible for the stabilization of the pyrochlore structure. The electrical properties of the LBT composition were studied and appeared as very similar to the one of “pure” Bi2Ti2O7. Because of its large thermal stability range, this pyrochlore phase appears to be a promising material for dielectric or tunability applications. [Display omitted] •Bi2Ti2O7 pyrochlore type phase was stabilized in Li2O-Bi2O3-TiO2 ternary system.•This phase exists in a large range of composition centered on (Li1/2Bi1/2)TiO3.•This phase is stable up to 1100 °C, against 600 °C for metastable “pure” Bi2Ti2O7.•The stabilization results from the substitution of part of the Bi-ions by lithium.•This phase appears as promising material for dielectric or tunability applications.