Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on (001) Nb-doped SrTiO3 (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a p-type semiconductor and formed a p-n heterojunction with an n-type semiconductor Nb-STO. The current density versus voltage (J-V) and capacitance versus voltage (C-V) characteristics of the heterojunction were investigated. A typical rectifying J-V effect was observed with a large rectifying ratio of 5×104. Reverse C-V characteristics exhibited a linear 1∕C2 versus V plot, from which a built-in potential of 0.6V was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.
In this work we analyze the influence of random point defects introduced by 3 MeV proton irradiation on the critical current density (J c ) and vortex dynamics of a Ba(Fe 0.925 Co 0.075 ) 2 As 2 single crystal. The results show that at low temperatures (T ) the irradiation produces an enhancement of J c of up to 2.6 times. However the J c (T ) retention at different magnetic fields (H ) in the elastic regime, estimated by the n exponent in J c vs (1 − (T /T c ) 2 ) n , is poorer after the irradiations due to the thermal softening of the pinning by the random point defects. We found that the elastic-to-plastic crossover and melting lines are only affected by the reduction of the superconducting critical temperature (T c ); they are exactly the same after rescaling the phase diagram by T /T c . The pinning mechanisms in the single crystals can be associated with a mixed pinning landscape that produces a modulation in S(H , T ) as a consequence of a fishtail or second peak in the magnetization.
Atomistic modeling shows that Cu-Nb and Cu-V interfaces contain high excess atomic volume due to constitutional vacancy concentrations of ~5%at. and ~0.8%at., respectively. This finding is supported by experiments demonstrating that a ~5-fold higher He concentration is required to observe He bubbles via throughfocus transmission electron microscopy at Cu-Nb interfaces than in Cu-V interfaces.Interfaces with structures tailored to minimize precipitation and growth of He bubbles may be used to design damage-resistant composites for fusion reactors.Unlike pure metals 1 , some materials contain constitutional vacancies that are thermodynamically stable at arbitrarily low temperature, for example grain boundaries (GBs) in ceramics 2 and semiconductors 3 , compounds with wide phase fields like NiAl 4 , and certain metal hydrides 5 . We use atomistic modeling to show that Cu-Nb and Cu-V interfaces contain high constitutional vacancy concentrations.Indirect experimental verification of this prediction is obtained by measuring the critical He concentration at which bubbles become detectable at these interfaces in transmission electron microscopy (TEM).
Ion irradiation experiments and atomistic simulations were used to demonstrate that irradiation-induced lattice swelling in a complex oxide, Lu2Ti2O7, is due initially to the formation of cation antisite defects. X-ray diffraction revealed that cation antisite formation correlates directly with lattice swelling and indicates that the volume per antisite pair is approximately 12 Å3. First principles calculations revealed that lattice swelling is best explained by cation antisite defects. Temperature accelerated dynamics simulations indicate that cation Frenkel defects are metastable and decay to form antisite defects.
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