Zhongwu Wang

X-ray diffraction and Raman spectroscopic study of nanocrystalline CuO under pressures

Compressibility of an oxide does not necessarily change due to decrease in particle size. This is found in nanocrystalline CuO, an important semiconductor. We studied nanometric CuO with high energy synchrotron radiation and Raman spectroscopic techniques to pressures of 47 GPa. Our results indicate that nanometric CuO has the same bulk modulus as observed in the macrometric CuO. Combination of results obtained from MgO, Ni, and e-Fe indicates that the contribution of the size-induced surface energy to total internal energy has very little effect on the high pressure behavior of this type of nanomaterials, in which their bulk counterparts exhibit the structural stability over a wide range of pressure. This result is contrary to some observations, showing that the reduction of particle size significantly leads to increased bulk modulus.

Pressure induced phase transformations in nanocrystalline maghemite (γ-Fe2O3)

Abstract Macro-crystalline γ-Fe 2 O 3 transforms to the α-Fe 2 O 3 structure at a pressure of 35xa0GPa. We performed a Raman spectroscopic study to explore the pressure induced phase transformation in nanocrystalline γ-Fe 2 O 3 to 57.5xa0GPa. We found that at a pressure of 26.6xa0GPa, there was a significant transformation of the γ-phase to α-structure. All Raman modes of the α-Fe 2 O 3 nanophase as extrapolated to 1xa0atm are higher than those observed in the bulk counterpart, and also exhibit lower pressure shifts, except one mode at 269.1xa0cm −1 . The α-Fe 2 O 3 phase transforms to a perovskite phase at ∼53.3xa0GPa, which is the same as that observed in the bulk material. Upon release of pressure to ambient conditions, the perovskite phase transforms to the α-Fe 2 O 3 phase by a slow distortional mechanism. The recovered α-Fe 2 O 3 phase exhibits the same Raman characteristics as those in the bulk sample. Particle size affects the transition pressure of the first phase transformation but does not affect the continuous post-phase transformations.

A simple model for assessing the high pressure melting of metals: nickel, aluminum and platinum

High-pressure melting has been of general interest for our understanding of solid-liquid phase transition due to the importance in high-pressure physics and material science, and here a simple mode ...

Volumetric properties and phase relations of silica — thermodynamic assessment

Taking into account various available experimental data, an improved internally consistent data set for the SiO2 system is obtained by thermodynamic assessment. The volumetric properties for SiO2 p ...

The melting of corundum (Al2O3) under high pressure conditions

We have developed a simple model to address the melting of corundum (Al2O3). For this simple model, a critical volume representative for the melting point was determined, and by employing the relat ...

Improved equations for addressing the high pressure melting of metastable silicate perovskites

Based on our previous thermodynamic model ol high pressure melting of any solid that is stable under ambient pressure (Wang et al., J. Alloys Comp. 299 (1000) 287-291), we have derived a few equati ...

The analysis on high pressure melting temperature dependence of the thermodynamic parameters of solids

Based on the relation between thermodynamic properties and temperature, one simple model has been developed to predict the melting of solids under high pressures. For this model, a critical tempera ...