Omega phase in materials

There is great interest in iron oxides, especially in nanosized form, for both fundamental and practical reasons. Because of its polymorphism, iron(III) oxide (ferric oxide, Fe2O3) is one of the most interesting and potentially useful phases of the iron oxides. Each of the four different known crystalline Fe2O3 polymorphs (alpha-, beta-, gamma-, and epsilon-Fe2O3) has unique biochemical, magnetic, catalytic, and other properties that make it suitable for specific technical and biomedical applications. High temperature treatment is a key step in most syntheses of iron(III) oxides but often triggers polymorphous transformations that result in the formation of undesired mixtures of Fe2O3 polymorphs. It is therefore important to control the parameters that induce polymorphous transformations when seeking to prepare a given Fe2O3 polymorph as a single phase; identifying and understanding these parameters is a major challenge in the study of the polymorphism of solid compounds. This review discusses the depende...

Polymorphous Transformations of Nanometric Iron(III) Oxide: A Review

The ruby luminescence method is widely used for pressure measurement in the diamond anvil cell and other optically transparent pressure cells. With this application in mind, we briefly review the ground-state physical properties of corundum (α-Al2O3) with some emphasis on its behavior under high pressure, survey the effects of temperature and stress on the R-line luminescence of ruby (Cr-doped corundum), and address the recent efforts towards an improved calibration of the R-line shift under hydrostatic pressures beyond the 50 GPa mark.

Ruby under pressure

The effects of uniaxial stress on the pressure-induced α → ω transition in pure titanium (Ti) are investigated by means of angle dispersive X-ray diffraction in a diamond-anvil cell. Experiments under four different pressure environments reveal that: (1) the onset of the transition depends on the pressure medium used, going from 4.9 GPa (no pressure medium) to 10.5 GPa (argon pressure medium); (2) the α and ω phases coexist over a rather large pressure range, which depends on the pressure medium employed; (3) the hysteresis and quenchability of the ω phase is affected by differences in the sample pressure environment; and (4) a short-term laser heating of Ti lowers the α → ω transition pressure. Possible transition mechanisms are discussed in the light of the present results, which clearly demonstrate the influence of uniaxial stress in the α → ω transition.

Pressure-induced α → ω transition in titanium metal: a systematic study of the effects of uniaxial stress

A description of the martensitic transformations between the , , and phases of titanium that includes nucleation and growth requires an accurate classical potential Optimization of the parameters of a modified embedded atom potential to a database of density-functional calculations yields an accurate and transferable potential as verified by comparison to experimental and density-functional data for phonons, surface and stacking fault energies, and energy barriers for homogeneous martensitic transformations Molecular-dynamics simulations map out the pressure-temperature phase diagram of titanium For this potential the martensitic phase transformation between and appears at ambient pressure and 1200 K, between and at ambient conditions, between and at 1200 K and pressures above 8 GPa, and the triple point occurs at 8 GPa and 1200 K Molecular-dynamics explorations of the kinetics of the martensitic - transformation show a fast moving interface with a low interfacial energy of 30 meV/A 2  The potential is applicable to the study of

Classical potential describes martensitic phase transformations between the α, β, and ω titanium phases

Impurity effects and reaction kinetics of the pressure-induced α→ω transformation in Ti

High pressure AC resistivity and compressibility study on Al2(WO4)3

High pressure and high temperature quench experiments on f -MnO 2 , Mn 2 O 3 and sol gel derived manganese oxides have been carried out to identify any new phases to which the materials may transform under high pressure and high temperature conditions Results of ESR, DTA and TGA investigations on sol gel derived manganese oxide have shown it to be hausmannite Mn 3 O 4 , instead of n -Mn 2 O 3 as reported earlier in the literature The sol gel derived manganese oxide transforms to n -Mn 2 O 3 when heated above 700°C Sol gel derived Mn 3 O 4 , when quenched from 5 GPa and temperature range 800-1200°C, gives a mixture of Mn 3 O 4 (hausmannite) and a phase having CaMn 2 O 4 (marokite)-type structure f -MnO 2 undergoes partial amorphization when pressure-quenched from 8 GPa at room temperature The high pressure and high temperature quench experiments up to 5 GPa and 700°C showed that the decomposition temperature of f -MnO 2 increases with pressure The new phase reported by Liu (1976) from diamond-anvil c

S. N. Vaidya

Papers

Impurity effects and reaction kinetics of the pressure-induced α→ω transformation in Ti

High pressure AC resistivity and compressibility study on Al2(WO4)3

High pressure and high temperature studies on manganese oxides

Mean-square atomic displacements in f.c.c. crystals

Toroid-anvil high-pressure high-temperature AC conductivity measurements on fast-ion conductors