To provide a complete picture of the energy landscape of Al 2 O 3 at the nanoscale, we directed this study toward understanding the energetics of amorphous alumina (a-Al 2 O 3 ). a-Al 2 O 3 nanoparticles were obtained by condensation from gas phase generated through laser evaporation of α-Al 2 O 3 targets in pure oxygen at25 Pa. As-deposited nanopowders were heat-treated at different temperatures up to 600 °C to provide powders with surface areas of 670−340 m 2 /g. The structure of the samples was characterized by powder X-ray diffraction, transmission electron microscopy, and solid-state nuclear magnetic resonance spectroscopy. The results indicate that the microstructure consists of aggregated 3−5 nm nanoparticles that remain amorphous to temperatures as high as 600 °C. The structure consists of a network of AlO 4 , AlO 5 , and AlO 6 polyhedra, with AlO 5 being the most abundant species. The presence of water molecules on the surfaces was confirmed by mass spectrometry of the gases evolved on heating the samples under vacuum. A combination of BET surface-area measurements, water adsorption calorimetry, and high-temperature oxide melt solution calorimetry was employed for thermodynamic analysis. By linear fit of the measured excess enthalpy of the nanoparticles as a function of surface area, the surface energy of a-Al 2 O 3 was determined to be 0.97 ± 0.04 J/m 2 . We conclude that the lower surface energy of a-Al 2 O 3 compared with crystalline polymorphs γand α-Al 2 O 3 makes this phase the most energetically stable phase at surface areas greater than 370 m 2 /g.

This work brings insights into the defect chemistry of YBZ solid solutions by measuring enthalpies of formation. We find a correlation between the obtained thermodynamic data and the known trend of the proton conductivity of YBZ solid solutions. This study is important for informed thermodynamic history-based materials selection and processing for specific applications.

The surface enthalpies of nanocrystalline CaTiO 3 and SrTiO 3 perovskites were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The nanocrystalline samples were synthesized by a hydrothermal method and characterized using powder X-ray diffraction, FTIR spectroscopy, and Brunauer-Emmett-Teller surface area measurements. The integral heats of water vapor adsorption on the surfaces of nanocrystalline CaTiO 3 and SrTiO 3 are À78.63 AE 4.71 kJ/mol and À69.97 AE 4.43 kJ/mol, respectively. The energies of the hydrous and anhydrous surfaces are 2.49 AE 0.12 J/m 2 and 2.79 AE 0.13 J/m 2 for CaTiO 3 and 2.55 AE 0.15 J/m 2 and 2.85 AE 0.15 J/m 2 for SrTiO 3 , respectively. The stability of the perovskite compounds in this study is discussed according to the lattice energy and tolerance factor approach. The energetics of different perovskites suggest that the formation enthalpy becomes more exothermic and surface energy increases with an increase in ionic radius of the "A" site cation (Ca, Sr, and Ba), or with the tolerance factor. PbTiO 3 shows a lower surface energy, weaker water binding, and a less exothermic enthalpy of formation than the alkaline-earth perovskites.

Water adsorption on the surface of LiCoO2 nanoparticles was investigated. As the water coverage increases the adsorption enthalpy decreases reaching the enthalpy of water condensation (−44 kJ mol−1). The experimentally observed average surface energy corresponding to all facets agree well with those reported from DFT calculations. The observed low surface energy is attributed to the surface Co3+ spin transition in nanophase LiCoO2.