Synthesis of Barium Titanate Using Deep Eutectic Solvents

Abstract

Novel synthetic routes to prepare functional oxides at lower temperatures are an increasingly important area of research. Many of these synthetic routes, however, use water as the solvent and rely on dissolution of the precursors, precluding their use with, for example, titanates. Here we present a low cost solvent system as a means to rapidly create phase-pure ferroelectric barium titanate using a choline chloride-malonic acid deep eutectic solvent. This solvent is compatible with alkoxide precursors and allows for the rapid synthesis of nanoscale barium titanate powders at 950 °C. The phase and morphology were determined, along with investigation of the synthetic pathway, with the reaction proceeding via BaCl2 and TiO2 intermediates. The powders were also used to create sintered ceramics, which exhibit a permittivity maximum corresponding to a tetragonal-cubic transition at 112 °C, as opposed to the more conventional temperature of ~ 120 °C. The lower-thanexpected value for the ferro-to para-electric phase transition is likely due to undetectable levels of contaminants.

Low‐temperature crystallization of La0.15Sr0.775TiO3 using ionic liquids

“…This initial crystallization of TiO 2 is rapidly followed by strontium carbonate (or more likely a mixed strontium/lanthanum carbonate phase), and interestingly, by 400°C the amount of anatase phase has been reduced to an undetectable level. This is key to the successful low‐temperature phase formation, as large quantities of TiO 2 (as observed in similar titanate syntheses) require elevated temperatures to react. The absence of TiO 2 is concurrent with the emergence of the LST phase (visible as a minor phase in the 400°C sample) indicating that the newly formed carbonate and anatase nanoparticles are acting as reaction sites, with the high surface area promoting rapid formation of the LST phase.…”

“…There are numerous schemes for the direction of crystal morphology in oxides. One such method is the use of ionic liquids or deep eutectic solvents to form transient intermediates which lower the reaction temperature required, either through a high degree of intermediate‐composition nanoparticle mixing, low temperature decomposition, or through complex eutectic mixtures of the reagents themselves. These types of synthesis lend themselves to technologically useful titanate materials as they enable easy incorporation of Ti ions from alkoxide precursors.…”

“…These types of synthesis lend themselves to technologically useful titanate materials as they enable easy incorporation of Ti ions from alkoxide precursors. Choline chloride/malonic acid deep eutectic solvents, for example, has been used to form barium titanate at reduced temperatures through the formation of titanium dioxide nanoparticles and barium chloride, which reacted at lower temperatures than typically encountered in solid‐state reactions . The nanoscale nature of the intermediates formed enabled easy egress of the chloride ions during heating, however, some concerns remain regarding the retention of small (often undetectable) quantities of the chloride ions which can have an effect on functionality …”

The role of ionic liquids in the synthesis of the high-temperature superconductor YBa2Cu3O7−δ

“…It has been proved however that chlorinated phases could also be used for the synthesis of metal oxides provided the temperature of calcination is high enough to allow for recombination. 40 Second, it is very important to identify, for every system, the precursory phases needed to form the target crystal phase. In this case copper oxide, yttrium copper oxide and barium carbonate were clearly identified as the precursor phases, consequently, allowing the formation of such phases at earlier stages will promote the synthesis of the target phase.…”

Synthesis and Dissolution of Metal Oxides in Ionic Liquids and Deep Eutectic Solvents

“…The same IL was used by Boston et al for the synthesis of a barium titanate precursor from barium acetate and titanium isopropoxide. However, the final oxide was obtained after 6-h calcination at 500 • C and 1 h at 950 • C [94].…”