Single crystal growth of CoTi₂O₅ by solid state reaction synthesis

Abstract

Materials in single crystal form are often sought after because the absence of grain boundaries can result in unique properties relative to the polycrystal, but producing these materials is typically a slow and complex process. In this work, pseudo single crystals of the pseudobrookite compound CoTi2O5 were synthesized by solid‐state reaction from a duplex grain mixture of CoTiO3 and TiO2. The size of the crystallites was >250 µm. The transformation and subsequent microstructural evolution of the CoTi2O5 was studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and X‐ray diffraction (XRD). A novel growth mechanism was identified whereby a single crystal CoTi2O5 front advances simultaneously along multiple CoTiO3/TiO2 diphasic boundaries. The single crystal domains were composed of subgrains approximately 5 µm in diameter; differences in the subgrain size and misorientation were related to the growth mechanism and the initial grain size of the duplex CoTiO3–TiO2 mixture. CoTi2O5 is a little characterized compound, and this study represents the most significant microstructural study of CoTi2O5 to date. The findings may be applied to similar pseudobrookite compounds such as MgTi2O5 and Al2TiO5.

Pseudo‐single crystal growth of the entropy‐stabilized compound CoTi2O5: Microstructural evolution and kinetics

“…It is worth mentioning that the EBSD maps show that within the transformation zone, the microstructure of the CDT consists of subgrains of similar, but not always identical orientation. In the prior study by Anderson et al., 30 the subgrain sizes were comparable to that of the initial duplex grain size, and it was postulated that the subgrain structure resulted from minor changes in orientation as the intergranular CDT grew past triple points.…”

“…The powder composition was designed to yield a 1:1 molar mixture of CoTiO 3 and TiO 2 . Details of the powder preparation have been described previously 30 . For the unseeded samples, the powder was uniaxially cold pressed (Carver, Wabash, IN) to a pressure of 65 MPa using a steel die assembly.…”

“…In systems such as MgO-Al 2 O 3 , the phase field of C (MgAl 2 O 4 ) lies between those of A (MgO) and B (Al 2 O 3 ) over a continuous span of temperature ranging from ambient to the molten state, hence any heat-treatment that would result in the co-sintering of the A and B reactant powders would also cause reaction to form C. For a compound such as CDT, however, by sintering at T < T c , it is possible to achieve an initial structure consisting of a dense, duplex mixture comprising solely CoTiO 3 and TiO 2 grains; subsequent reaction to CDT takes place only if the system temperature is increased to above Tc. Using this strategy, Anderson et al 30 studied the transformation to CDT in agglomerated powder particles. It was observed that rather than (the expected) multiple random nucleation at the diphase boundaries, the CDT formed as a pseudo-single crystal and grew inward from the surface, propagating along the boundaries between the CoTiO 3 and TiO 2 grains.…”

Use of metamodels for rapid discovery of narrow bandgap oxide photocatalysts

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Revealing electronic structure of nanostructured cobalt titanate via a combination of optical and electrochemical approaches toward water splitting and CO2 reduction

“…CoTiO 3 can be prepared by various methods such as solid‐state reaction, 22 modified Pechini method, 14 sol–gel method 23 and so on. The morphology of the materials, which depends on the preparation method, plays an important role in surface phenomena like heterogeneous water splitting and CO 2 reduction.…”