No abstract

To improve photoelectrochemical (PEC) activity of hematite, the modification of energy band by doping 3d transition metal ions Cu and Ti into α-Fe2O3 were studied via the first-principles calculations with density function theory (DFT)+U method. The results show that the band gap of hematite is ∼2.1 eV and n-type dopant Ti improves the electric conductivity, confirmed by recent experiments. The p-type dopant Cu enhances the utilization ratio of solar energy, shifts both valance, and conduction band edges to a higher energy level, satisfying hydrogen production in the visible light driven PEC water splitting without voltage bias.

An analytical solution shows that the maximal strain of an impurity-free metallic monatomic chain (MC), or a defect-free nanowire (NW), varies inapparently with mechanical stress but apparently with the separation between the melting point ͓T m ͑K͔͒ and the temperature of operation in terms of exp͕͓T m ͑K͒ − T͔ −1 ͖, where K is the dimension of the NW (for a MC, K = 1.5). Reconciliation of the measured data of Au-MC breaking limit suggests that the discrepancy in measurement arises from thermal and mechanical fluctuations near the T m of the MC that is ͑1 / 4.2͒-fold of the bulk value. Findings also favor the mechanism for the high extensibility of a nanograined NW and further indicate that bond unfolding of the lower-coordinated atoms dominates the grain boundary activities, particularly at temperatures approaching surface melting.

Orientation-engineered 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) thin films were deposited on La0.7Sr0.3MnO3-coated SrTiO3 single-crystalline (001), (110), and (111) substrates by off-axis radio-frequency magnetron sputtering. X-ray diffraction confirmed a highly epitaxial growth of all the as-deposited films. It is believed the strong orientation dependence of ferroelectric and piezoelectric properties on the films is attributed to the relative alignment of crystallites and spontaneous polarization vector. The optimal ferroelectric response lies in the [001] direction, whereas a comparatively large effective piezoelectric coefficient d33,eff of 100.1 ± 5 pm/V was attained in [111] BZT-BCT thin film, suggesting its potential application for high-performance lead-free piezoelectric devices.