Structure and properties of Bi2Ti2O7 pyrochlore type phase stabilized by lithium

Abstract

A study of the Li 2 O-Bi 2 O 3-TiO 2 ternary system evidenced a Bi 2 Ti 2 O 7 pyrochlore phase in a large range of composition, centered on (Li 1/2 Bi 1/2)TiO 3 (LBT). This composition led to a pyrochlore phase stable up to 1100°C, while pure Bi 2 Ti 2 O 7 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" Bi 2 Ti 2 O 7 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" Bi 2 Ti 2 O 7. Because of its large thermal stability range, this pyrochlore phase appears to be a promising material for dielectric or tunability applications.

Ab Initio and Experimental Insights on Structural, Electronic, Optical, and Magnetic Properties of Cr-Doped Bi2Ti2O7

“…This is one of the reasons for the low thermal stability of the stoichiometric Bi 2 Ti 2 O 7 phase . The substitution of part bismuth cations to the others with a smaller ionic radius can improve its stability. − Furthermore, the new doped compounds can exhibit novel properties, which differ from those of the pure BTO.…”

Highly transparent Bi4Ti3O12 thin-film electrodes for ferroelectric-enhanced photoelectrochemical processes

“…This phase, which has often been observed both in Bi 4 Ti 3 O 12 powder samples and films [52][53][54][55][56][57][58][59][60][61][62][63][64] depending on synthesis temperature, Bi:Ti molar ratio, substrate, and film growth condition, has been proven to decompose at temperatures higher than 600°C ( †ESI, Figure S1), in accordance with the literature. 65 However, such heating conditions cannot be employed in the fabrication of the BiTO layers due to the use of FTO-coated glass substrates ( †ESI, section S1). As it is shown, because of the thin nature of the deposited layers, in the spin-coated samples FTO peaks are predominant in intensity compared to the BiTO ones, and secondary phases could not be detected.…”

“…S1 †), in accordance with the literature. 65 However, such heating conditions cannot be employed in the fabrication of the BiTO layers due to the use of FTO-coated glass substrates (ESI, Section S1 †). As is shown, because of the thin nature of the deposited layers, in the spin-coated samples FTO peaks are predominant in intensity compared to the BiTO ones, and secondary phases could not be detected.…”

Low-temperature synthesis of bismuth titanate by modified citrate amorphous method

“…Moreover, the Bi 2 Ti 2 O 7 pyrochlore phase is a well-known secondary phase that can appear during the production of the BiT [15,36]. This pyrochlore phase is metastable at temperatures higher than 650 °C [23,37], thereby it is not observed in the samples treated at 700 °C and 800 °C. Another specific feature in the XRD pattern (Figure 2) is the narrowing of the diffraction peaks with the increase in the calcination temperature.…”