Titanium oxides have many fascinating optical and electrical properties, such as the superconductivity at 2 K in cubic titanium monoxide (TiO) polycrystalline bulk. However, the lack of TiO single crystals or epitaxial films has prevented systematic investigations on its superconductivity. Here, we report the basic superconductivity characterizations of cubic TiO films epitaxially grown on (0001)-oriented α-Al 2 O 3 substrates. The magnetic and electronic transport measurements confirmed that TiO is a type-II superconductor and the recorded high T c is about 7.4 K. The lower critical field (H c1 ) at 1.9 K, the extrapolated upper critical field H c2 (0), and coherence length are about 18 Oe, 13.7 T, and 4.9 nm, respectively. With increasing pressure, the value of T c shifts to lower temperature while the normal state resistivity increases. Our results on the superconducting TiO films confirm the strategy to achieve higher T c in the epitaxial films, which may be helpful for finding more superconducting materials in various related systems.

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The vortex phase transition in BaFe1.8Co0.2As2 single crystals was studied systematically via measuring the current–voltage (I-V) characteristics by rotating the crystals in magnetic fields from H // c to H // ab. The angle-resolved I-V curves clearly show a three-dimensional vortex glass (VG) scaling collapse. The angular dependent VG transition field Hg and critical current density Jc can be approximately described by the anisotropic Ginzburg-Landau model, and no peaks representing c-axis correlated pinning were recorded for H // c, which reveals that the vortex pinning is mainly caused by randomly distributed uncorrelated-defects. While in the vicinity of H // ab, Jc deviates from the model due to the in-plane intrinsic pinning. Based on the above results, the angle-resolved vortex phase diagram is constructed, indicating the anisotropic superconducting properties of the system.

The photovoltaic properties of YBa2Cu3O7−δ/Nb-doped SrTiO3 (SNTO) heterostructures were investigated systematically under laser irradiation of different wavelengths from 365 nm to 640 nm. A clear photovoltaic effect was observed, and the photovoltage Voc ranged from 0.1 V to 0.9 V depending on the wavelength. The Voc appeared under laser illumination with a photon energy of 2.4 eV, far below the band gap (3.2 eV) of Nb-doped SrTiO3. The temperature dependencies of the Voc and short-current density showed kinks near the structural phase transition of the Nb-doped SrTiO3. Our findings are helpful for understanding the photovoltaic effect in transition-metal oxide based heterojunctions and designing such photovoltaic devices.

A series of uni-axial tensile cycling tests were conducted at room temperature in superelastic NiTi strip specimens with nano-grain size. The NiTi superelastic strip specimen's Apparent Young's Modulus (AYM) and the critical stress decrease when the specimen is subjected to an external uni-axial stress and the strain being higher than 1.5%. Both of the AYM and the critical stress become steady after 10-time cycling. The number of the (111)½1 4 43 oriented grains increases with extending the strain value. The sub-grain size grows with increasing mechanical cycling number due to the annihilation of the small angle boundaries. The AYM-softening is related to the grain re-orientation (texture evolution) and the formation of irreversible-stabilized B19 0 martensitic variants. The softness of the critical stress is principally attributed to the aspect that the grains re-orient to align along the two textural components (111)½1 1 10 and (111)½1 4 43 when the external stress being applied. The rotation of grains towards the observed orientation gives higher Schmid factor for the transformation and is one of the reasons for the decrease in AYM and critical stress. The orientation relationships between B2 parent phase and the strain-induced B19 0 martensite are observed to be:

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There are many fascinating properties in titanium oxides such as the enhanced superconductivity in cubic TiO epitaxial thin films with the superconducting transition temperature of 7.65 K, which is much higher than that of the bulk polycrystalline TiO. To explore the superconductivity of the TiO thin films in more detail, we investigated the magnetic field and temperature dependences of the current–voltage (I–V) characteristics and the critical current density Jc in magnetic fields perpendicular to the film surface. The I–V curves show a quasi-two-dimensional vortex glass (VG) scaling collapse in different magnetic fields, and a vortex phase diagram is constructed from the VG and vortex liquid regions to the normal state. Through the critical current density investigation, we found that δl pinning dominates the pinning behavior, which is in accordance with the analyzed results of the vortex pinning force associated with defects in the film, such as grain boundaries. The findings of the magnetic phase diagram and critical current properties should be helpful for practical applications of the TiO family.