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The resistive functional layer in SrFeOx (SFO) topological phase transition (TPT) memristors is typically epitaxially grown on a perovskite bottom electrode and thus the bottom electrode plays an important role in the microstructure and resistive switching performance of the SFO functional layer. Unfortunately, the excessive diffusion of oxygen in the bottom electrode to SrFeOx causes uncontrollable distortion of the microstructure of the resistive functional layer, thereby compromising the overall device properties. In this study, SFO films were epitaxially grown on two different bottom electrodes of La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) using pulsed laser deposition (PLD). The SFO memristor with a LSMO electrode exhibits excellent cycling stability, ON/OFF ratio, data retention, and endurance performance. In addition, the phase constituents, superlattice-like stripes and elemental valence states of SFO/LSMO and SFO/SRO hetero-structures were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. Furthermore, the oxygen migration free energy barriers of the bottom electrodes in the two devices were calculated by first-principles. All the above research results indicate that the LSMO electrode, being less prone to diffuse oxygen ions, significantly contributes to the superior structural stability and enhanced performance of the SFO/LSMO heterostructure. Finally, the energy band structures and Schottky barriers between BM-SFO and the top electrode of Au and the bottom electrode of LSMO were analyzed by ultraviolet photoelectron spectroscopy and ultraviolet-visible spectroscopy, which provide experimental insights into explaining its conductive mechanism. [ABSTRACT FROM AUTHOR]

An ideal catalyst should have a relative hydrogen adsorption Gibbs free energy (ΔGH) close to zero [J. K. Nørskov, et al., J. Electrochem. Soc., 2005, 152, J23]. However, most of the known catalysts cannot reach this standard. Based on first-principles calculations, we studied the hydrogen evolution reaction (HER) catalytic performance of pristine and defect (including vacancy and heteroatom doping) structures in terms of its ΔGH. We found that the ΔGH values of Co-doped HfS2 and P-doped HfSe2 are extremely close to zero, even closer than that of Pt (111), indicating that they are excellent catalysts. Moreover, we found that the source of the HER catalytic performance of Co-doped HfS2 is the reduction of electron accumulation of the active site S atom. Our work provides two potential ideal catalysts and provides guidance for the experimental group to search for suitable catalysts. [ABSTRACT FROM AUTHOR]

BiFeO3 is the only material with ferroelectric Curie temperature and Néel temperature higher than room temperature, making it one of the most well-studied multiferroic materials. Based on an ab initio evolutionary algorithm, we predicted a new cubic C-type antiferromagnetic structure (Fd3¯m-BiFeO3) at ambient pressure. It was found that Fd3¯m-BiFeO3 is the hardest BiFeO3 (Vickers hardness ∼ 9.12 GPa), about 78% harder than R3c-BiFeO3 (the well-known multiferroic material), which contributes to extending the life of BiFeO3 devices. In addition, Fd3¯m-BiFeO3 has the largest shear modulus (83.74 GPa) and the largest Young's modulus (214.72 GPa). Besides, we found an interesting phenomenon that among the common multiferroic materials (BiFeO3, BaTiO3, PbTiO3, SrRuO3, KNbO3, and BiMnO3), Pnma-BiMnO3 has the largest bulk modulus, and its bulk modulus is about 15% larger than that of Fd3¯m-BiFeO3. However, its Vickers hardness (4.47 GPa) is much smaller than that of Fd3¯m-BiFeO3. This is because the Vickers hardness is proportional to the shear modulus and the shear modulus of Fd3¯m-BiFeO3 is larger than that of Pnma-BiMnO3. This work provides a deeper and more comprehensive understanding of BiFeO3. [ABSTRACT FROM AUTHOR]

BiFeO3 is one of the most widely studied multiferroic materials, because of its large spontaneous polarization at room temperature, as well as ferroelasticity and antiferromagnetism. Using an ab initio evolutionary algorithm, we found two new dynamically stable BiFeO3 structures (P63 and P6322) at ambient pressure. Their energy is only 0.0662 and 0.0659 eV per atom higher than the famous R3c–BiFeO3, and they have large spontaneous polarization, i.e., 71.82 μC cm−2 and 86.06 μC cm−2, respectively. The spontaneous polarization is caused by the movement of the Bi3+ atom along the [001] direction and mainly comes from the 6s electron of Bi3+. Interestingly, there is no lone pair electron of Bi3+, which is different from R3c–BiFeO3. The new structures have the same magnetic configurations as R3c–BiFeO3 (G-type antiferromagnetism), but they are characterized by one-dimensional channels linked by a group of two via surface-sharing oxygen octahedra. Due to the similarity of the two structures, both of them have indirect bandgap structures, and the bandgaps are 2.62 eV and 2.60 eV, respectively. This work not only broadens the structural diversity of BiFeO3 but also has constructive significance for the study of spontaneous polarization of new structures of multiferroic materials. [ABSTRACT FROM AUTHOR]

An ideal catalyst should have a relative hydrogen adsorption Gibbs free energy (Δ G H ) close to zero [J. K. Nørskov, et al., J. Electrochem. Soc. , 2005, 152 , J23]. However, most of the known catalysts cannot reach this standard. Based on first-principles calculations, we studied the hydrogen evolution reaction (HER) catalytic performance of pristine and defect (including vacancy and heteroatom doping) structures in terms of its Δ G H . We found that the Δ G H values of Co-doped HfS 2 and P-doped HfSe 2 are extremely close to zero, even closer than that of Pt (111), indicating that they are excellent catalysts. Moreover, we found that the source of the HER catalytic performance of Co-doped HfS 2 is the reduction of electron accumulation of the active site S atom. Our work provides two potential ideal catalysts and provides guidance for the experimental group to search for suitable catalysts.

BiFeO 3 is the only material with ferroelectric Curie temperature and Néel temperature higher than room temperature, making it one of the most well-studied multiferroic materials. Based on an ab initio evolutionary algorithm, we predicted a new cubic C-type antiferromagnetic structure ( Fd 3̄ m -BiFeO 3 ) at ambient pressure. It was found that Fd 3̄ m -BiFeO 3 is the hardest BiFeO 3 (Vickers hardness ∼ 9.12 GPa), about 78% harder than R 3 c -BiFeO 3 (the well-known multiferroic material), which contributes to extending the life of BiFeO 3 devices. In addition, Fd 3̄ m -BiFeO 3 has the largest shear modulus (83.74 GPa) and the largest Young's modulus (214.72 GPa). Besides, we found an interesting phenomenon that among the common multiferroic materials (BiFeO 3 , BaTiO 3 , PbTiO 3 , SrRuO 3 , KNbO 3 , and BiMnO 3 ), Pnma -BiMnO 3 has the largest bulk modulus, and its bulk modulus is about 15% larger than that of Fd 3̄ m -BiFeO 3 . However, its Vickers hardness (4.47 GPa) is much smaller than that of Fd 3̄ m -BiFeO 3 . This is because the Vickers hardness is proportional to the shear modulus and the shear modulus of Fd 3̄ m -BiFeO 3 is larger than that of Pnma -BiMnO 3 . This work provides a deeper and more comprehensive understanding of BiFeO 3 .

BiFeO 3 is one of the most widely studied multiferroic materials, because of its large spontaneous polarization at room temperature, as well as ferroelasticity and antiferromagnetism. Using an ab initio evolutionary algorithm, we found two new dynamically stable BiFeO 3 structures ( P 6 3 and P 6 3 22) at ambient pressure. Their energy is only 0.0662 and 0.0659 eV per atom higher than the famous R 3 c -BiFeO 3 , and they have large spontaneous polarization, i.e. , 71.82 μC cm -2 and 86.06 μC cm -2 , respectively. The spontaneous polarization is caused by the movement of the Bi 3+ atom along the [001] direction and mainly comes from the 6s electron of Bi 3+ . Interestingly, there is no lone pair electron of Bi 3+ , which is different from R 3 c -BiFeO 3 . The new structures have the same magnetic configurations as R 3 c -BiFeO 3 (G-type antiferromagnetism), but they are characterized by one-dimensional channels linked by a group of two via surface-sharing oxygen octahedra. Due to the similarity of the two structures, both of them have indirect bandgap structures, and the bandgaps are 2.62 eV and 2.60 eV, respectively. This work not only broadens the structural diversity of BiFeO 3 but also has constructive significance for the study of spontaneous polarization of new structures of multiferroic materials.