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In this work, a modified sintering method, i.e. the three-step sintering technology, has been applied to fabricate the K0.5Na0.5NbO3 ceramics. The impact of the detailed sintering conditions on the...

Electrocaloric (EC) refrigeration, is accepted as an auspicious method to develop eco-friendly cooling devices. Here, the investigations on the EC response and energy storage performance of heterovalent-doped Ba(Sn, Ti)O3 relaxor ferroelectrics are carried out. Doping of aliovalent Mn or Nb elements into Ti site would regulate both the EC and energy storage behaviors. An enhanced EC temperature change up to 1.31 K, and a maximal recoverable energy storage density of 0.24 J cm− 3 with the efficiency as high as 87.11 %, can be observed under 70 kV cm− 1 in 0.5 % acceptor-doped Ba(Sn, Ti)O3 ceramics. It is found that the local internal stress, the local charge fluctuation, and the oxygen deficiencies would benefit the electrical behaviors of this system. These results would shed light on the effect of the heterovalent substitution on the electrical properties of lead-free BaTiO3 system and provide a novel and simple route to further improve the EC response and energy storage performance.

Two-dimensional electron gas (2DEG) at the interface between two insulating perovskite oxides has attracted much interest for both fundamental physics and potential applications. Here, we report the discovery of a new 2DEG formed at the interface between spinel MgAl

Organolead trihalide perovskites have attracted substantial interest with regard to applications in charge-based photovoltaic and optoelectronic devices because of their low processing costs and remarkable light absorption and charge transport properties. Although spin is an intrinsic quantum descriptor of a particle and spintronics has been a central research theme in condensed matter physics, few studies have explored the spin degree of freedom in the emerging hybrid perovskites. Here, we report the characterization of a spin valve that uses hybrid perovskite films as the spin-transporting medium between two ferromagnetic electrodes. Because of the light-responsive nature of the hybrid perovskite, a high magnetoresistance of 97% and a large spin-diffusion length of 81 nm were achieved at 10 K under light illumination in polycrystalline films. Furthermore, by using thin perovskite single crystals, we discovered that the spin-diffusion length was able to reach 1 μm at low temperatures. Our results indicate that the spin relaxation is not significant as previously expected in such lead-containing materials and demonstrate the potential of low-temperature-processed hybrid perovskites as new active materials in spintronic devices.

The search for new superconductors capable of carrying loss-free current has been a research theme in condensed matter physics for the past decade. Among superconducting compounds, titanates have not been pursued as much as Cu2+ (3d9) (cuprate) and Fe2+ (3d6) (pnictide) compounds. Particularly, Ti3+-based compounds or electron systems with a special 3d1 filling are thought to be promising candidates as high-TC superconductors, but there has been no report on such pure Ti3+-based superconducting titanates. With the advent of thin-film growth technology, stabilizing new structural phases in single-crystalline thin films is a promising strategy to realize physical properties that are absent in the bulk counterparts. Herein, we report the discovery of unexpected superconductivity in orthorhombic-structured thin films of Ti2O3, a 3d1 electron system, which is in strong contrast to the conventional semiconducting corundum-structured Ti2O3. This is the first report of superconductivity in a titanate with a pure 3d1 electron configuration. Superconductivity at 8 K was observed in the orthorhombic Ti2O3 films. Leveraging the strong structure-property correlation in transition-metal oxides, our discovery introduces a previously unrecognized route for inducing emergent superconductivity in a newly stabilized polymorph phase in epitaxial thin films. Researchers have discovered a titanate -based single-crystal film with a rare structure that allows superconductivity to emerge at low temperatures. Titanium (III) oxide, Ti2O3, has garnered recent interest for solar and energy harvesting devices because its electrons are easily excited by electromagnetic radiation. A team led by Tom Wu from University of New South Wales in Sydney, Australia and Shuai Dong from Southeast University in Nanjing, China, report that these electrons have a very high density comparable to metals and are strongly coupled with lattice in constrained thin films. The researchers used a sapphire substrate to direct the growth of nanometer-thick Ti2O3 layers into a solid-state structure not normally found in free-grown crystals. One particular combination of growth temperature and film thickness yielded an orthorhombic crystal phase that exhibited an unusual semiconductor-to-superconductor electronic transition when cooled to 8 K. Polymorph-dependent superconductivity was discovered in orthorhombic-structured Ti2O3 thin films, which is in strong contrast to the conventional semiconducting trigonal corundum-structured Ti2O3. Leveraging on the strong structure-property correlation in transition-metal oxides, our discovery introduces a hitherto unrecognized route towards inducing superconductivity in 3d1 electron systems via polymorph engineering.

Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode-type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO3-SrTiO3 interface. Tunable insulator-to-metal transitions, absent in the individual components, are observed as a result of the competing temperature-dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler-Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials.

Titanium nitride (TiN) exhibits extremely high wear resistance and corrosion resistance, leading to a broad range of applications. Despite the extensive theoretical efforts on the structural stability of TiN under pressure, a few experimental observations of the pressure-induced phase transition through x-ray diffraction are still in debate. Here, the Raman spectra of TiN under pressure are studied in a diamond anvil cell up to 36 GPa. The discontinuity in the pressure dependent phonon frequencies suggests a phase transition at around 5 GPa with the bonding between Ti and N hardly changing. The phase transition is ascribed to an isostructural transition or a vacancy filling mechanism.

The compositional manipulation of the multiphase coexistence in relaxor–ferroelectrics has been reported to be an effective approach to generate the giant electrocaloric effect. In this work, we systemically investigate the temperature-dependent electrocaloric effect in BaZr0.18Ti0.82O3–BaSn0.11Ti0.89O3 relaxors, where Zr and Sn are introduced into BaTiO3 to develop the multiphase coexistence at the ferroelectric–paraelectric transition. Through the direct measurement by the heat flux sensor, a large temperature change around 4 K under an electric field of 10 MV m−1, combined with a broad temperature span (20 °C–60 °C), has been observed. For comparison, the electrocaloric properties are also indirectly deduced based on Maxwell equations and Landau–Ginzburg–Devonshire phenomenological theory, and the validity of the indirect methods in this relaxor–ferroelectric system has been discussed. This work would shed light on developing giant electrocaloric materials with a wide operating temperature range.

A large-sized CuZr-based bulk metallic glass (BMG) composite with enhanced mechanical properties is prepared successfully. With the addition of Ta to CuZr-based alloys, the critical composite size changes and the microstructure diversifies. The composite with 0.5 at.% Ta addition has the largest critical size with the microstructure of single CuZr(B2) phase uniformly dispersing in amorphous matrix. This composite exhibits good mechanical properties, i.e., large compressive plasticity and work-hardening ability, which should be attributed to the uniformly distributed CuZr(B2) phase. The increased critical size of CuZr-based BMG composite can be explained by the fact that proper Ta addition can suppress the precipitation of crystalline phases other than B2 CuZr phase during solidification. This study may be helpful for the fabrication of large-sized BMG composites with excellent mechanical properties.

Vacancy engineering can effectively modulate the optical and electronic properties of metal oxides. Here, we demonstrate that high-pressure could be a clean strategy to tune the vacancies in oxides with a high cationic vacancy content. By combining in situ synchrotron x-ray diffraction, Raman scattering, and charge transport measurements in a diamond anvil cell, we systematically study the structure and electrical properties of TiO with ∼16% ordered vacancies up to 50.2 GPa at room temperature. The monoclinic TiO transforms to the cubic phase at ∼37.8 GPa. After decompression to ambient conditions, the cubic phase survives. The vacancies are partially filled and become disordered with a concentration of approximately 12.5%. The charge transport of TiO at high pressure exhibits a metal-insulator transition, which originates from the ordered to disordered transition of vacancies under pressure. Molecular dynamics simulations suggest that the vacancies enhance the mobility of atoms in the lattice under pressure and lead to the pressure-induced amorphization and recrystallization.Vacancy engineering can effectively modulate the optical and electronic properties of metal oxides. Here, we demonstrate that high-pressure could be a clean strategy to tune the vacancies in oxides with a high cationic vacancy content. By combining in situ synchrotron x-ray diffraction, Raman scattering, and charge transport measurements in a diamond anvil cell, we systematically study the structure and electrical properties of TiO with ∼16% ordered vacancies up to 50.2 GPa at room temperature. The monoclinic TiO transforms to the cubic phase at ∼37.8 GPa. After decompression to ambient conditions, the cubic phase survives. The vacancies are partially filled and become disordered with a concentration of approximately 12.5%. The charge transport of TiO at high pressure exhibits a metal-insulator transition, which originates from the ordered to disordered transition of vacancies under pressure. Molecular dynamics simulations suggest that the vacancies enhance the mobility of atoms in the lattice under press...

We investigated the influence of minor additions of B, Al and Nb that have representative atomic sizes on the glass forming ability (GFA) and stability of Zr-Ni amorphous alloys during mechanical alloying. The results show that the minor addition of B, Al or Nb does not shorten the initial time of the full amorphization reaction or improve the glass forming ability of the Zr-Ni alloys at a low rotation speed. However, B addition can effectively improve the mechanical stability of the amorphous phase against mechanically induced crystallization. Furthermore, the amorphous phase gradually transforms into a metastable fcc-phase with increasing milling time. The addition of Al and Nb that have similar atomic sizes has a similar effect on the GFA and the mechanical stability of the Zr-Ni amorphous phase. Moreover, Al and Nb addition can alter the crystallization behavior and improve the thermal stability of the Zr-Ni amorphous phase.

Materials with mesoscopic structural and electronic phase separation, either inherent from synthesis or created via external means, are known to exhibit functionalities absent in the homogeneous counterparts. One of the most notable examples is the colossal magnetoresistance discovered in mixed-valence manganites, where the coexistence of nano- to micrometer-sized phase-separated domains dictates the magnetotransport. However, it remains challenging to pattern and process such materials into predesigned structures and devices. In this work, a direct laser interference irradiation (LII) method is employed to produce periodic stripes in thin films of a prototypical phase-separated manganite Pr0.65 (Ca0.75 Sr0.25 )0.35 MnO3 (PCSMO). LII induces selective structural amorphization within the crystalline PCSMO matrix, forming arrays with dimensions commensurate with the laser wavelength. Furthermore, because the length scale of LII modification is compatible to that of phase separation in PCSMO, three orders of magnitude of increase in magnetoresistance and significant in-plane transport anisotropy are observed in treated PCSMO thin films. Our results show that LII is a rapid, cost-effective and contamination-free technique to tailor and improve the physical properties of manganite thin films, and it is promising to be generalized to other functional materials.

In this paper, we investigate the electric field effect on epitaxial Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films in electric double-layer transistors. Different from the conventional transistors with semiconducting channels, the sub(micrometer)-scale phase separation in the manganite channels is expected to result in inhomogeneous distribution of mobile carriers and local enhancement of electric field. The field effect is much larger in the low-temperature phase separation region compared to that in the high-temperature polaron transport region. Further enhancement of electroresistance is achieved by applying a magnetic field, and a 250% modulation of resistance is observed at 80 K, equivalent to an increase of the ferromagnetic metallic phase fraction by 0.51%, as estimated by the general effective medium model. Our results illustrate the complementary nature of electric and magnetic field effects in phase-separated manganites, providing insights on such novel electronic devices based on complex oxides. Published version

We report the electrostatic modulation of transport in strained Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films grown on SrTiO3 by gating with ionic liquid in electric double layer transistors (EDLT). In such manganite films with strong phase separation, a cluster glass magnetic state emerges at low temperatures with a spin freezing temperature of about 99 K, which is accompanied by the reentrant insulating state with high resistance below 30 K. In the EDLT, we observe bipolar and asymmetric modulation of the channel resistance, as well as an enhanced electroresistance up to 200% at positive gate bias. Our results provide insights on the carrier-density-dependent correlated electron physics of cluster glass systems. Published version

Many commonly used electrical resistive switching devices are based on films of metal-oxide-metal ``sandwiches.'' Now scientists have observed ultrafast and reversible resistive switching in a thin-film device composed of a metallic platinum layer and two ultrathin layers of insulating oxides, LaAlO${}_{3}$ and SrTiO${}_{3}$, and revealed its origin in the oxides' charge-carrying oxygen vacancies.

We report that electrode engineering, particularly tailoring the metal work function, measurement configuration and geometric shape, has significant effects on the bipolar resistive switching (RS) in lateral memory devices based on self-doped SrTiO3 (STO) single crystals. Metals with different work functions (Ti and Pt) and their combinations are used to control the junction transport (either ohmic or Schottky-like). We find that the electric bias is effective in manipulating the concentration of oxygen vacancies at the metal/STO interface, influencing the RS characteristics. Furthermore, we show that the geometric shapes of electrodes (e.g., rectangular, circular, or triangular) affect the electric field distribution at the metal/oxide interface, thus plays an important role in RS. These systematic results suggest that electrode engineering should be deemed as a powerful approach toward controlling and improving the characteristics of RS memories. Published version

We report on the magnetic properties of cuprate/manganite bilayers composed of antiferromagnetic (AFM) La2CuO4 and ferromagnetic La0.70Sr0.30MnO3. The temperature dependent magnetization data indicate an interfacial spin-glass state. Furthermore, the bilayer exhibits significant enhancement of coercivity compared to the La0.70Sr0.30MnO3 single layer and reaches 705 Oe at 5 K. The dependence of coercivity on the AFM layer thickness indicates that the enhancement cannot be explained by the interfacial charge diffusion. Our results suggest that the exchange coupling between Mn and Cu spins and the magnetic frustration at the La2CuO4/La0.70Sr0.30MnO3 interface must be considered to harness the properties of cuprate/manganite heterostructures. Published version

International audience; Emerging physical phenomena at the unit-cell-controlled interfaces of transition-metal oxides have attracted lots of interest because of the rich physics and application opportunities. This work reports a reentrant spin glass behavior with strong magnetic memory effect discovered in oxide heterostructures composed of ultrathin manganite La 0.7 Sr 0.3 MnO 3 (LSMO) and cuprate La 2 CuO 4 (LCO) layers. These heterostructures are featured with enhanced ferromagnetism before entering the spin glass state a Curie temperature of 246 K is observed in the superlattice with six-unit-cell LSMO layers, while the reference LSMO film with the same thickness shows much weaker magnetism. Furthermore, an insulator–metal transition emerges at the Curie temperature, and below the freezing temperature the superlattices can be considered as a glassy ferromagnetic insulator. These experimental results are closely related to the interfacial spin reconstruction revealed by the first-principles calculations, and the dependence of the reentrant spin glass behavior on the LSMO layer thickness is in line with the general phase diagram of a spin system derived from the infinite-range SK model. The results of this work underscore the manganite/cuprate superlattices as a versatile platform of creating artificial materials with tailored interfacial spin coupling and physical properties. © 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

This work was supported in part by the National Research Foundation, Singapore (Grant No. NRF-CRP4-2008-04).

Solid oxide electrolyser cells (SOECs) have been considered effective to produce hydrogen at a high conversion efficiency through high temperature electrolysis (HTE) process and has a potential to scale up to a large-scale economy hydrogen source. The crucial issue for the SOEC moving into practical applications is stability. In this paper, investigation was conducted with the focus on the anode degradation using SOEC cells with strontium doped lanthanum manganite (LSM) anode and strontium doped lanthanum ferro-cobaltites (LSCF) anode. The results showed a more stable performance in LSM cells than LSCF cells when testing at 750ºC anode degradation and anode delamination contributed most of performance drop. The LSM cell is thus more suitable for HTE than the LSCF cell due to its better bonding between the electrolyte and anode.