Structures and Role of the Intermediate Phases on the Crystallization of BaTiO3 from an Aqueous Synthesis Route.

Kristine Bakken,Viviann H Pedersen,Koji Ohara,Tor Grande,Anders B Blichfeld,Satoshi Tominaka,Inger-Emma Nylund,Mari-Ann Einarsrud

doi:10.1021/acsomega.1c00089

Abstract

Carbonate formation is a prevailing challenge in synthesis of BaTiO3, especially through wet chemical synthesis routes. In this work, we report the phase evolution during thermal annealing of an aqueous BaTiO3 precursor solution, with a particular focus on the structures and role of intermediate phases forming prior to BaTiO3 nucleation. In situ infrared spectroscopy, in situ X-ray total scattering, and transmission electron microscopy were used to reveal the decomposition, pyrolysis, and crystallization reactions occurring during thermal processing. Our results show that the intermediate phases consist of nanosized calcite-like BaCO3 and BaTi4O9 phases and that the intimate mixing of these along with their metastability ensures complete decomposition to form BaTiO3 above 600 °C. We demonstrate that the stability of the intermediate phases is dependent on the processing atmosphere, where especially enhanced CO2 levels is detrimental for the formation of phase pure BaTiO3.

Highlights

The thermodynamic stability of BaCO3 poses a common synthesis challenge for producing BaTiO3, which is a ferroelectric material widely used in capacitors.[1]
A second stabilizing mechanism was proposed by Ischenko et al.: topotaxial formation of structural domains of calcite-type carbonate (BaCO3 (C)) by templating with oxygen-deficient Ti-rich BaTiO3-like structures.[20]
The models for the intermediate phases have been proposed, it is not known how these phases are affected by processing conditions, such as the heating rate, annealing temperature, and atmosphere, and the intermediate phases influence the formation of BaTiO3

Summary

Introduction

The thermodynamic stability of BaCO3 poses a common synthesis challenge for producing BaTiO3, which is a ferroelectric material widely used in capacitors.[1] The stability of BaCO3 relative to BaTiO3 increases with a high partial pressure of CO2 in the atmosphere and analogously with the activity (concentration) of CO2 in water.[2] the solubility of BaCO3 in water is limited,[3] which combined with the thermodynamic stability makes carbonate secondary phases prevalent both in solid-state reactions and aqueous processing of BaTiO3 materials. Wet chemical synthesis studies of BaTiO3-based powders and thin films generally report BaCO3 compounds as intermediate and secondary phases.[1,5] Using sol−gel-related methods based on organic solvents, the precursors tend to decompose to form aragonite-type carbonate (BaCO3 (A))

Results

Discussion

Conclusion