Thermodynamics of Nanoscale Calcium and Strontium Titanate Perovskites

Sahu, Sulata K.; Maram, Pardha Saradhi; Navrotsky, Alexandra

doi:10.1111/jace.12622

Cited by 25 publications

(31 citation statements)

References 42 publications

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“…Since all nanocrystalline samples contain adsorbed water on their surfaces, the ΔHds values were corrected for water content following procedures described previously 41,50 . Since all nanocrystalline samples contain adsorbed water on their surfaces, the ΔHds values were corrected for water content following procedures described previously 41,50 .…”

Section: ) Calculation Of Surface and Formation Enthalpiesmentioning

confidence: 99%

“…High-temperature oxide melt solution calorimetry has been successfully demonstrated to measure the surface energies of an array of binary and ternary oxides directly 41,45,46 but not yet for alkali tantalate and niobate perovskites.…”

Section: Introductionmentioning

confidence: 99%

“…a) shows variation of formation enthalpies of alkali tantalates and niobates with their surface energies, along with the reported formation enthalpies and surface energetics of selected perovskite titanates: CaTiO3, SrTiO3, BaTiO3 and PbTiO341,63 . The perovskites having more exothermic enthalpies of formation, ΔHf ox , appear to have higher surface energies.…”

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confidence: 99%

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Thermodynamic stability of lead-free alkali niobate and tantalate perovskites

et al. 2015

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Lead free niobates and tantalates currently form one of the most promising groups of ferroelectrics, piezoelectrics and related materials, with important applications for the next generation of lead free sensors, actuators and microelectromechanical systems (MEMs). In view of their importance, the enthalpies of formation from binary oxide components at 25 °C, measured by high temperature oxide melt solution calorimetry of a set of alkali tantalates and niobates with perovskite-like structures, LiTaO3, LiNbO3, NaTaO3, NaNbO3 and KNbO3 are reported to be -93.kJ/mol for LiTaO3, LiNbO3, NaTaO3, NaNbO3 and KNbO3, respectively. The surface energies of nanocrystalline perovskites of these alkali tantalates and niobates were experimentally determined for the first time by calorimetry. The energies of the hydrated surface are 1.04 ± 0.34, 1.21 ± 0.78, 1.58 ± 0.29, 2.16 ± 0.57 and 2.95 ± 0.59 J/m 2 for LiTaO3, LiNbO3, NaTaO3, NaNbO3 and KNbO3, respectively. The stability of the lead-free perovskites of I-V type is discussed based on their tolerance factor and acid-base chemistry. The formation enthalpy becomes more exothermic (higher thermodynamic stability) and surface energy increases (greater destabilization for a given particle size) with increase in ionic radius of the A-site cation (Li, Na and K) and with increasing tolerance factor. These correlations provide key insights into how lead free niobates and tantalates behave during synthesis and processing;i.e they explain, for example, why KNbO3 and KTaO3 nanoparticles will be thermodynamically more reactive than their Li and Na counterparts. This understanding will facilitate the development of optimized processing techniques and applications.

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Section: ) Calculation Of Surface and Formation Enthalpiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermodynamic stability of lead-free alkali niobate and tantalate perovskites

et al. 2015

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“…The surface enthalpies (referring to hydrated surfaces) were determined from the drop solution enthalpies as described in our previous work 41,44 . The surface enthalpies (referring to hydrated surfaces) were determined from the drop solution enthalpies as described in our previous work 41,44 .…”

Section: Mn 3 O 4 and The Bulk And Nano (1-x)fe 3 O 4 -Xco 3 O 4 And mentioning

confidence: 99%

“…Surface energy calculations from high temperature drop solution calorimetry data were completed as described in earlier studies41 . Before the drop solution experiments, all samples were equilibrated at 25 ˚C and 50 ± 5 % humidity in the calorimetry suite, and the water contents of these equilibrated samples were determined using TGA as described in the previous section.…”

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confidence: 99%

Thermodynamics of Fe₃O₄–Co₃O₄and Fe₃O₄–Mn₃O₄spinel solid solutions at the bulk and nanoscale

Sahu

Huang

Lilova

et al. 2015

Phys. Chem. Chem. Phys.

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High temperature oxide melt solution calorimetry has been performed to investigate the enthalpies of mixing (ΔmixH) of bulk and nanophase (1 -x)Fe3O4-xM3O4 (M = Co, Mn) spinel solid solutions. The entropies of mixing (ΔmixS) were calculated from the configurational entropies based on cation distributions, and the Gibbs free energies of mixing (ΔmixG) were obtained. The ΔmixH and ΔmixG for the (1 -x)Fe3O4-xCo3O4 system are negative over the complete solid solution range, for both macroscopic and nanoparticulate materials. In (1 -x)Fe3O4-xMn3O4, the formation enthalpies of cubic Fe3O4 (magnetite) and tetragonal Mn3O4 (hausmannite) are negative for Mn3O4 mole fractions less than 0.67 and slightly positive for higher manganese content. Relative to cubic Fe3O4 and cubic Mn3O4 (stable at high temperature), the enthalpies and Gibbs energies of mixing are negative over the entire composition range. A combination of measured mixing enthalpies and reported Gibbs energies in the literature provides experimental entropies of mixing. The experimental entropies of mixing are consistent with those calculated from cation distributions for x > 0.3 but are smaller than those predicted for x < 0.3. This discrepancy may be related to the calculations, having treated Fe(2+) and Fe(3+) as distinguishable species. The measured surface energies of the (1 -x)Fe3O4-xM3O4 solid solutions are in the range of 0.6-0.9 J m(-2), similar to those of many other spinels. Because the surface energies are relatively constant, the thermodynamics of mixing at a given particle size throughout the solid solution can be considered independent of the particular particle size, thus confirming and extending the conclusions of a recent study on iron spinels.

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