Martensitic Phase Transition in Yttrium-Stabilized ZrO2 Nanopowders by Adsorption of Water

The present study was aimed at revealing the influence of the mechanical stress induced by water molecules adsorption on the composition of crystalline phases in the ZrO2–3mol%Y2O3-nanoparticles. Three basic methods have been used to determine the phase transition: neutron diffraction, Raman microspectroscopic scanning, and X-ray diffraction. The fact of phase-structural β → α transformation and the simultaneous presence of two polymorphic structural modifications (β is the phase of the tetragonal syngony and α of monoclinic syngony in nanosized particles (9nm)) under normal physical conditions was established by these methods. Satisfactory consistency was achieved between the results obtained using different techniques.

Martensitic Phase Transition in Yttrium-Stabilized ZrO2 Nanopowders by Adsorption of Water

The present study was aimed at revealing the influence of the mechanical stress induced by water molecules adsorption on the composition of crystalline phases in the ZrO2–3mol%Y2O3-nanoparticles. Three basic methods have been used to determine the phase transition: neutron diffraction, Raman microspectroscopic scanning, and X-ray diffraction. The fact of phase-structural β → α transformation and the simultaneous presence of two polymorphic structural modifications (β is the phase of the tetragonal syngony and α of monoclinic syngony in nanosized particles (9nm)) under normal physical conditions was established by these methods. Satisfactory consistency was achieved between the results obtained using different techniques.

Phase Transition in Iron Thin Films Containing Coherent Twin Boundaries: A Molecular Dynamics Approach

Using molecular dynamics (MD) simulation, the austenitic and martensitic phase transitions in pure iron (Fe) thin films containing coherent twin boundaries (TBs) have been studied. Twelve thin films with various crystalline structures, thicknesses and TB fractions were investigated to study the roles of the free surface and TB in the phase transition. In the austenitic phase transition, the new phase nucleates mainly at the (112)bcc TB in the thicker films. The (111¯)bcc free surface only attends to the nucleation, when the film is extremely thin. The austenitic transition temperature shows weak dependence on the film thickness in thicker films, while an obvious transition temperature decrease is found in a thinner film. TB fraction has only slight influence on the austenitic temperature. In the martensitic phase transition, both the (1¯10)fcc free surface and (111)fcc TB attribute to the new body-center-cubic (bcc) phase nucleation. The martensitic transition temperature increases with decreased film thickness and TB fraction does not influent the transition temperature. In addition, the transition pathways were analyzed. The austenitic transition obeys the Burgers pathway while both the Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) relationship are observed in the martensitic phase transition. This work may help to understand the mechanism of phase transition in the Fe nanoscaled system containing a pre-existing defect.

Normal-to-topological insulator martensitic phase transition in group-IV monochalcogenides driven by light

A material potentially exhibiting multiple crystalline phases with distinct optoelectronic properties can serve as a phase-change memory material. The sensitivity and kinetics can be enhanced when the two competing phases have large electronic structure contrast and the phase change process is diffusionless and martensitic. In this work, we theoretically and computationally illustrate that such a phase transition could occur in the group-IV monochalcogenide SnSe compound, which can exist in the quantum topologically trivial Pnma-SnSe and nontrivial $$Fm\bar 3m$$Fm3¯m-SnSe phases. Furthermore, owing to the electronic band structure differences of these phases, a large contrast in the optical responses in the THz region is revealed. According to the thermodynamic theory for a driven dielectric medium, optomechanical control to trigger a topological phase transition using a linearly polarized laser with selected frequency, power and pulse duration is proposed. We further estimate the critical optical electric field to drive a barrierless transition that can occur on the picosecond timescale. This light actuation strategy does not require fabrication of mechanical contacts or electrical leads and only requires transparency. We predict that an optically driven phase transition accompanied by a large entropy difference can be used in an “optocaloric” cooling device.

Эластокалорический эффект в быстрозакаленном сплаве Ti-=SUB=-2-=/SUB=-NiCu при периодическом воздействии растягивающей силы с частотой до 50 Hz

The elastocaloric effect (ECE) is studied in samples of rapidly quenched ribbons of a Ti_2NiCu alloy at a periodic action by a mechanical stress to 300 MPa at a frequency to 50 Hz. ECE is maximal near the temperatures of a first-order thermoelastic martensitic phase transition. The ECE maximum is observed in a point corresponding to the completion of the reverse martensitic transition ( T = 67.5°C) and is 21 and 6 K at cyclic mechanical loads of 300 and 100 MPa, respectively. The ECE value is shown to be independent of the frequency of the external loads in the range from 0 to 50 Hz. The specific power of a rapidly quenched ribbon as a thermal energy transformer is estimated at the external mechanical stress of 100 MPa; its value is 150 W/g at a frequency of 50 Hz and ECE is 6 K.

Structure Determination of Er Doped Ti-Al-Nb Alloy by Neutron Diffraction Analysis

Neutron diffraction experiments with both conventional powder diffraction setup and under in-situ compressive loading were conducted to investigate the structural origins of large strength and toughness enhancements in Ti-16Al-27Nb alloy after Er addition. The primary phase is determined to be the ordered B2 structure form, in agreement with the previous electron microscopy study. Lattice strains of {210} and {100} planes were measured as a function of applied stress, and elastic anisotropy was found for both, and strong plastic nonlinearity was discovered for (210) reflection. The grain refinement during plastic deformation was proposed by both the 2D diffraction intensity distribution and SEM observations, while stress-induced martensitic phase transition was not observed in this study. It is believed that the activation of different slip systems and grain refinement might be the structural origin of the novel mechanical properties of this alloy.