Phase Transition Path Research Articles

Microstructure, morphology and their annealing behaviors of alumina films synthesized by ion beam assisted deposition

Alumina films have been synthesized by ion beam assisted deposition (IBAD). X-ray photoelectron spectroscopy (XPS) and Rutherford back-scattering (RBS) analysis show that films synthesized by IBAD are stoichiometrical Al 2O 3 films. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction analysis (XRD) have been applied to characterize the microstructures and morphologies of Al 2O 3 films and their annealing behaviors. We have found that the films are dominated by amorphous Al 2O 3 phase when the substrate temperatures are lower than 500 °C. The path of phase transition of film is amorphous Al 2 O 3 → 800 ° C/6 h rgamma -Al 2 O 3 → 1000 ° C/6 h γ-Al 2 O 3+ α-Al 2 O 3 → 1200 ° C/2 h α-Al 2 O 3 . The film morphology is related with the phase transition of films during annealing.

EpitaxialPb(Zr,Ti)O3thin films with coexisting tetragonal and rhombohedral phases

Epitaxial ${\mathrm{P}\mathrm{b}(\mathrm{Z}\mathrm{r},\mathrm{}\mathrm{T}\mathrm{i})\mathrm{O}}_{3}$ thin films having coexisting tetragonal and rhombohedral phases have been successfully fabricated with the film compositions that correspond to the Zr-rich region of the morphotropic phase boundary (MPB). The key to the present success is to quantitatively understand the shift of the MPB under a film stress. The present fabrication has been theoretically justified by superimposing the computed temperature-dependent film stress on the theoretical temperature-stress (T-S) phase diagram and by delineating a probable phase-transition path upon cooling the film from the processing temperature.

In situ composite formation in TiAlSi ternary system

Abstract Three stoichiometric TiAlSi-based metastable alloys (i.e. Ti14Al21Si, Ti11Al21Si and Ti9Al27Si, at.%) have been synthesized by mechanical alloying (MA). It has been found, by means of X-ray diffraction (XRD) and transmission electron microscope (TEM), that these metastable phases (or precursors) are mainly in nano-structures, with partially amorphous phases as for the alloy Ti14Al21Si. Importantly, investigation of these metastable phases during heating (by using differential thermal analysis, DTA) shows a hierarchical change in phase transition, and particularly Ti 5 Si3 is in situ formed via a phase transition path TiSi 2 →TiSi→Ti 5 Si 4 →Ti 5 Si 3 . This is meaningful in materials design using a kinetics bias strategy. Microstructures of fully densified Ti 5 Si 3 /TiAl in situ composites have been observed by optical microscope.

Transition paths between phases IV, III and II of ammonium nitrate predicted from X-ray powder diffractometer and differential scanning calorimeter data by partial least-squares regression

Ammonium nitrate solid phase transition paths between phases IV, III and II were explained and predicted on the basis of X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) data by applying partial least-squares regression (PLS) and principal component analysis (PCA). The samples were clustered according to their different transition paths with the PLS and PCA models, and the transition paths were predicted with PLS component clusters. The best PLS clusters were formed by a few first components. Prediction of the transition path with the PLS clusters made a semiquantitative prediction of the transition energy possible. In PCA, principal components 6 and 11, which best clustered the samples, explained 7% of the variation of the XRD data. The clustering showed that most of the variance is due to other factors than those affecting the transition path. The correlation between the structural data and the transition energies obtained by differential scanning calorimetry was calculated by PLS method. The correlation between the predicted and the observed energies of an independent predictor set varied from zero to over 0.7 depending on the 2θ range. The PLS analysis of the XRD and DSC measurements proved that the different phase transition paths are of structural origin.

DSC studies on the effect of particle size on NH 4NO 3 at temperatures between 25 and 100°C

According to DSC measurements, NH 4NO 3 samples with particle sizes between 0.062 and 2 mm have different structural phase transition paths in the temperature range 25–100°C. Samples with particle sizes of about 2 mm underwent the transition path IV→III→II, whereas those with particle size near 0.06 mm were more likely to undergo the transition path IV→II.

Effect of the crystallization on the phase transitions IV ⇐ III and IV ⇐ II of ammonium nitrate

The solid state phase transition path of ammonium nitrate is influenced by the manner of crystallization. Slow crystallization from water gives ideal crystals, which behaved differently from crystals prepared by rapid crystallization from the melt.