Role of entropy in the stability of cobalt titanates

Jacob, Κ. T.; Rajitha, G.

doi:10.1016/j.jct.2010.02.016

Cited by 22 publications

(20 citation statements)

References 20 publications

(64 reference statements)

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“…Similar to the other pseudobrookite compounds, the mixing of cations on particular crystallographic sites results in the entropy stabilization of CoTi 2 O 5 . 15 The phase diagram predicts that CoTi 2 O 5 will undergo eutectoid decomposition below ~1140°C to CoTiO 3 + TiO 2 , however, as seen in this study, depending on the heat-treatment conditions, CoTi 2 O 5 can be retained at room temperature.…”

Section: Introductionmentioning

confidence: 51%

“…Single crystal CoTi 2 O 5 has been produced through a melt process utilizing an optical floating zone furnace, however the solid‐state single crystal growth demonstrated in this work has not been previously reported in this system. Similar to the other pseudobrookite compounds, the mixing of cations on particular crystallographic sites results in the entropy stabilization of CoTi 2 O 5 . The phase diagram predicts that CoTi 2 O 5 will undergo eutectoid decomposition below ~1140°C to CoTiO 3 + TiO 2 , however, as seen in this study, depending on the heat‐treatment conditions, CoTi 2 O 5 can be retained at room temperature.…”

Section: Introductionmentioning

confidence: 54%

“…The standard Gibbs free energy change for the reaction in Equation was determined by Jacob and Rajitha to be:

Δ G_{2}^{0} \pm 76 / false(J \cdot {mol}^{- 1} false) = 13 400 - 9.474 false(T false/ K false)

…”

Section: Discussionmentioning

confidence: 99%

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Single crystal growth of CoTi₂O₅ by solid state reaction synthesis

et al. 2019

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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.

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Section: Introductionmentioning

confidence: 51%

Section: Introductionmentioning

confidence: 54%

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Single crystal growth of CoTi₂O₅ by solid state reaction synthesis

et al. 2019

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“…because the Gibbs free energy of formation of CoTiO 3 [20] is less negative than that of FeTiO 3 [18]. When the two displacement reactions are away from equilibrium, in addition to the dissociation of NiTiO 3 according to reaction (4), there is an additional titanate dissociation reaction involving CoTiO 3 :…”

Section: Complex Microstructuresmentioning

confidence: 99%

“…Consider the couple Fe-(Mg 0:5 Co 0:5 /TiO 3 . Because the Gibbs energy of formation of MgTiO 3 is very much more negative than those of CoTiO 3 [20] and FeTiO 3 [18], metallic Fe will not reduce MgTiO 3 component of the ilmenite solid solution. Metallic Fe will only displace Co in the ilmenite solid solution, resulting in a microstructure consisting of Fe-Co alloy and a ternary oxide solid solution (Mg,Co,Fe)TiO 3 .…”

Section: Complex Microstructuresmentioning

confidence: 99%

Reactive Interdiffusion: A Method for Making Composition Graded Metal-ceramic Composites

Reddy

Jacob

Rajitha

2012

High Temperature Materials and Processes

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Presented is a new method for making composition graded metal-ceramic composites using reactive interdiffusion between a metal and a complex ceramic. Composition variation in both metal and ceramic phases with distance along the direction of diffusion is achieved. The design criteria for developing such composites are discussed. The system should exhibit extensive solid solubility in both metallic and ceramic phases, a defined gradation in the stabilities of the oxides, and mobility of electrons or holes in the oxide solid solution. The complex ceramic used for making the composite should be polycrystalline with sufficient porosity to accommodate the volume expansion caused by alloy precipitation. An inert atmosphere to prevent oxidation and high processing temperature to facilitate diffusive transport are required. The process is illustrated using the reaction couples Fe-NiTiO 3 , Fe-(Mg,Co)TiO 3 and Fe-(Ni,Co)TiO 3 .

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