Impact of Oxalate Ligand in Co-Precipitation Route on Morphological Properties and Phase Constitution of Undoped and Rh-Doped BaTiO3 Nanoparticles

Abstract

In order to design and tailor materials for a specific application like gas sensors, the synthesis route is of great importance. Undoped and rhodium-doped barium titanate powders were successfully synthesized by two routes; oxalate route and classic route (a modified conventional route where solid-state reactions and thermal evaporation induced precipitation takes place). Both powders were calcined at different temperatures. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX) and Brunauer-Emmet-Teller (BET) analyses are employed to identify the phases and polymorphs, to determine the morphology, the chemical composition and the specific surface area of the synthesized materials, respectively. The so-called oxalate route yields pure BaTiO3 phase for undoped samples at 700 °C and 900 °C (containing both cubic and tetragonal structures), while the classic route-synthesized powder contains additional phases such as BaCO3, TiO2 and BaTi2O5. Samples of both synthesis routes prepared by the addition of Rh contain no metallic or oxide phase of rhodium. Instead, it was observed that Ti was substituted by Rh at temperatures 700 °C and 900 °C and there was some change in the composition of BaTiO3 polymorph (increase of tetragonal structure). Heat-treatments above these temperatures show that rhodium saturates out of the perovskite lattice at 1000 °C, yielding other secondary phases such as Ba3RhTi2O9 behind. Well-defined and less agglomerated spherical nanoparticles are obtained by the oxalic route, while the classic route yields particles with an undefined morphology forming very large block-like agglomerates. The surface area of the synthesized materials is higher with the oxalate route than with the classic route (4 times at 900 °C). The presence of the oxalate ligand with its steric hindrance that promotes the uniform distribution and the homogeneity of reactants could be responsible for the great difference observed between the powders prepared by two preparation routes.

Hydrothermal Synthesis of Iridium-Substituted NaTaO3 Perovskites

“…The materials we have prepared show stability on heating in air to only 600 • C, which demonstrates how it would be impossible to prepare the same samples by conventional solid-state synthesis, or even coprecipitation methods that require an annealing step. It is interesting to note that Rh 3+ -containing BaTiO 3 prepared by an oxalate-aided coprecipitation route showed extrusion of rhodium metal when heated above its synthesis temperature [30]. This illustrates the tendency for the precious metals to be reduced, but also how this may be aided by embedding in a host lattice by replacement of a cation of higher charge.…”

“…LaCr 1−x M x O 3 (LCMO) (x = 0.01, 0.05, 0.10 with M = Pd, Co, Ir) materials were prepared using conventional solid-state synthesis from single metal oxide precursors at 1200 • C, with a reduction in band gap observed for all substituted materials [29]. Rh-doped BaTiO 3 nanoparticles, with 2% of the substituent, were prepared by a co-precipitation route using oxalate as solution additive at temperatures between 700 and 900 • C [30]. The Rh was found in the +3 oxidation state and on heating to higher temperatures the rhodium was lost, with phase transformation of the perovskite.…”

Solution‐Based Synthesis Routes for the Preparation of Noncentrosymmetric 0‐D Oxide Nanocrystals with Perovskite and Nonperovskite Structures

“…The chelating‐agent assisted synthesis of BaTiO 3 was reported several decades ago and was, since then, largely reproduced, in particular with the aim of elaborating new multifunctional transition metal or rare‐earth doped BaTiO 3 nanocrystals that combine, for instance, SHG and up‐conversion emission properties. [ 151,152 ] However, if the synthesis method efficiently produces BaTiO 3 nanocrystals, the required thermal annealing inevitably induces particle aggregation. Among the oldest papers, one can mention the synthesis of cubic and tetragonal BaTiO 3 nanocrystals in the 50–300 nm size range that can be easily obtained after a thermal decomposition above 550°C of barium titanyl oxalate (BaTiO(C 2 O 4 ) 2 ·4H 2 O).…”

“…As a consequence, the crystallization of BaTiO 3 is observed at 700 °C, leading to nanostructured, spherical but still aggregated nanopowders. [ 151 ] Very interestingly, a recent study demonstrates the importance of time‐resolved in situ infrared and XRD measurements to elucidate the formation mechanism of BaTiO 3 nanocrystals after drying at 150 °C of a mixture of Ti‐ and Ba‐solutions stabilized with citric acid and EDTA. If crystallization above 500 °C results from the reaction between two poorly crystallized, intermediate metastable phases (namely BaTi 4 O 9 and a calcite‐type BaCO 3 ), lowering the CO 2 partial pressure has been found key to avoid the formation of stable carbonates.…”

Electrospun Fibre Webs Templated Synthesis of Mineral Scaffolds Based on Calcium Phosphates and Barium Titanate

“…Moving to the possibility of local stimulation at the affected area, this can be achieved by using piezoelectric, ferroelectric, or ferromagnetic materials that are distributed in a controlled manner and activated by the application of external electric or magnetic fields, subsequently improving the speed and quality of tissue regeneration by modifying the biological routes travelled by the cells [45]. One such example is barium titanate (BaTiO 3 ), which is a well-known ceramic with unique properties [16,[46][47][48][49]. It was demonstrated that the integration of hydroxyapatite and barium titanate powders in a collagen matrix can improve the osseointegration process of the resulting hybrid scaffolds [47], the influence of barium titanate being afterwards evaluated through numerical simulation [46].…”