Constitutive Relationship and Hot Processing Maps of Mg-Gd-Y-Nb-Zr Alloy

The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain rate range of 703-773 K and 0.01-5 s^（-1）, respectively. Improved Arrhenius-type equation incorporated with strain compensations was used to predict flow behavior of the alloy, and the predictability was evaluated using correlation coefficient, root mean square error and absolute relative error. Processing maps were constructed at different strains for Mg-Gd-Y-Nb-Zr alloy based on dynamic materials model.The processing maps are divided into three domains and the corresponding microstructure evolutions are referred to the forming of straight grain boundaries, twinning, dynamic recrystallization and grain growth. Instability occurred mainly at the strain rate range of 0.3s^（-1）-0.5s^（-1）. The optimum processing domain is mainly at the temperature range of 703-765 K with the strain rate range of 0.01-0.1 s^（-1）.

Bond valence parameters linearly dependent on the molybdenum oxidation states

Based on the available crystal data, a linear correlation between R0, the bond valence parameter for a Mo-containing chemical bond, and the Mo oxidation state n was developed for the first time. Using the 'universal' value of the parameter B = 0.037 nm, the linear equations of R0-n for Mo-X (X: O, S, N, Cl and F) bonds were established. The oxidation-state independent Mo-O bond valence parameters, R0 = 0.18788 nm and B = 0.03046 nm, published recently have been shown to be a special case of the linearly correlated functions. Some bond valence sum calculations in compounds containing only Mo-O bonds using these parameters are presented.

Photoinduced small electron polarons generation and recombination in hematite

Polarons generally affect adversely the photochemical and photophysical properties of transition metal oxides.However,the excited-state dynamics of polarons are not fully established to date and thus require an atomistic understanding.We focus onα-Fe_(2)O_(3)with photoexcitation,electron injection,and heterovalent doping as the small polaron models,and conduct simulations of ab initio adiabatic molecular dynamics(AIMD)and nonadiabatic molecular dynamics(NA-MD).The elaborately designed AIMD simulations show that localization of electron at a single Fe site is an adiabatic and ultrafast process within sub-15 fs.Fe_(2)O_(3)doping with an electron or a Si and Ti dopant forms a localized electron polaron while photoexcitation forms localized electron and hole polarons simultaneously,leading to diverse electron–hole recombination dynamics.NA-MD simulations demonstrate that recombination of an electron polaron created by doping with a delocalized hole at the valence band maximum ofα-Fe_(2)O_(3)takes place around 5 ps,while recombination between a pair of small electron and hole polarons in photoexcited Fe_(2)O_(3)delays to about 110 ps owing to weak NA coupling and fast decoherence process.The ultrafast formation of small electron polarons inα-Fe_(2)O_(3)impedes the accumulation of delocalized holes in the valence band that directly participate in water oxidation at photoanodes.The detrimental effect can be partially circumvented in photoexcited Fe_(2)O_(3)for slowing electron–hole recombination despite polarons may retain low charge mobility.These findings provide a fundamental understanding of the excited-state dynamics of small electron polaron inα-Fe_(2)O_(3)and may help design efficient transition metal oxides photoanodes.