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We report an electron transport study of an La-doped perovskite oxide BaSnO3 thin film grown by molecular beam epitaxy on (110) DyScO3 as a function of electron concentration, by etching the film step-by-step with nanometer precision. Inductively coupled plasma-reactive ion etching with BCl3/Ar plasma is used for etching depth control. The local doping and electron density are experimentally determined after each etching step. The results show that the electron mobility is dominated by threading dislocations if the electron concentration is below 7.8 × 1019 cm−3, while ionized impurities and phonon scattering become more dominant at electron concentrations greater than 1.2 × 1020 cm−3. The charging state of thread dislocations is estimated to be 6.2. Furthermore, using the etch process to control the electron concentration and channel thickness, a gate-recessed ferroelectric field effect transistor is fabricated with 10 nm HfO2 as a gate dielectric. The device exhibits a saturation current of 29.9 mA/mm with a current on/off ratio of Ion/Ioff = 8.3 × 108 and a ferroelectric polarization charge density of 1.9 × 1013 cm−2. Under the forward gate bias sweep, the device operates in the enhancement mode with a threshold voltage of 3 V. Under the reverse gate sweeping bias, the device operates in the depletion mode with a threshold voltage of –1.5 V. [ABSTRACT FROM AUTHOR]

Abstract: Atomic resolution Z-contrast images from a series of CeO2 [001] tilt grain boundaries at coincident site lattice (CSL) or near-CSL misorientations can all be explained within a structural unit model. These structural units (which cover all boundaries from 0° to 90°) show striking similarities to comparable CSL boundaries observed in cubic crystal structures that are also derived from dense packing (face centered cubic metal; rocksalt, perovskite, etc.). A general model for the structure of grain boundaries in such similarly structured materials systems has been developed that is based on the crystallography of the parent structures. Changes away from these predicted grain boundary symmetries can be interpreted as showing the frustration of symmetry caused by the incorporation of point defects (vacancies and impurities). This general model for grain boundary structures can, in principle, provide a means to infer the structure–property relationships in broad classes of materials. [Copyright &y& Elsevier]

Double perovskites such as Sr2CrReO6 attract great scientific attention owing to their high Curie temperatures (TC ≥ 550 K) as well as large magnetoresistances. However, both the specific physical mechanism of high TC and magnetic ground state in Sr2CrReO6 remain ill‐defined. In order to clarify and understand these issues, we studied its critical phase transition characteristics using critical behavior analysis. We found that the obtained critical exponents (β = 1.115 and γ = 2.224) are quite different from any traditional universality class. The abnormal critical behavior implies that at the quantum critical point, Sr2CrReO6 exists a strong competition among several magnetic interactions. By analyzing their effective critical exponents, we show that the double perovskite Sr2CrReO6 is really an ordered and homogeneous ferromagnet. With the help of Takahashi's theory, the nature of ferromagnetism in Sr2CrReO6 is confirmed to be localized instead of itinerant. The results of this research will provide new insights into the origins of high TC as well as the magnetic ground state in this double perovskite. [ABSTRACT FROM AUTHOR]

A key to the unique combination of electronic and optical properties in halide perovskite materials lies in their rich structural complexity. However, their radiation sensitive nature limits nanoscale structural characterization requiring dose efficient microscopic techniques in order to determine their structures precisely. In this work, we determine the space-group and directly image the Br halide sites of CsPbBr3, a promising material for optoelectronic applications. Based on the symmetry of high-order Laue zone reflections of convergent-beam electron diffraction, we identify the tetragonal (I4/mcm) structural phase of CsPbBr3 at cryogenic temperature. Electron ptychography provides a highly sensitive phase contrast measurement of the halide positions under low electron-dose conditions, enabling imaging of the elongated Br sites originating from the out-of-phase octahedral rotation viewed along the [001] direction of I4/mcm persisting at room temperature. The measurement of these features and comparison with simulations yield an octahedral rotation angle of 6.5°(±1.5°). The approach demonstrated here opens up opportunities for understanding the atomic scale structural phenomena applying advanced characterization tools on a wide range of radiation sensitive halide-based all-inorganic and hybrid organic-inorganic perovskites. [ABSTRACT FROM AUTHOR]

In an effort to explore new electronic devices with multiple functionalities, there are numerous studies of depositing perovskite oxides on flexible substrates to replace rigid silicon‐based wafer in device applications. In this study, the growth of pseudocubic SrRuO3 single‐crystal thin film on a transparent and flexible muscovite is established. The experimental results confirm that the Curie temperature TC and the magnetic properties can be effectively tuned via the mechanical strain due to the facilitation of flexible substrate. It is found that the tensile strain increases while the compressive strain decreases the spontaneous magnetization for the thin film suffering the same ±0.24% strain. Based on the study of critical behavior, the critical exponents β = 0.543(19) and γ = 1.262(1) with the critical temperature TC = 159.04(5) K and TC = 159.10 K, respectively, are obtained by the modified Arrott plot. The set of critical exponents matches well with Widom scaling relation and the scaling equation, indicating these critical exponents are intrinsic for SrRuO3 thin films. Moreover, it is achieved that the SrRuO3 thin films exhibit a long‐range interaction coupled with 3D‐Heisenberg type. [ABSTRACT FROM AUTHOR]

Adequate hole mobility is the prerequisite for dopant‐free polymeric hole‐transport materials (HTMs). Constraining the configurational variation of polymer chains to afford a rigid and planar backbone can reduce unfavorable reorganization energy and improve hole mobility. Herein, a noncovalent conformational locking via S–O secondary interaction is exploited in a phenanthrocarbazole (PC) based polymeric HTM, PC6, to fix the molecular geometry and significantly reduce reorganization energy. Systematic studies on structurally explicit repeats to targeted polymers reveals that the broad and planar backbone of PC remarkably enhances π–π stacking of adjacent polymers, facilitating intermolecular charge transfer greatly. The inserted "Lewis soft" oxygen atoms passivate the trap sites efficiently at the perovskite/HTM interface and further suppress interfacial recombination. Consequently, a PSC employing PC6 as a dopant‐free HTM offers an excellent power conversion efficiency of 22.2 % and significantly improved longevity, rendering it as one of the best PSCs based on dopant‐free HTMs. [ABSTRACT FROM AUTHOR]

Adequate hole mobility is the prerequisite for dopant‐free polymeric hole‐transport materials (HTMs). Constraining the configurational variation of polymer chains to afford a rigid and planar backbone can reduce unfavorable reorganization energy and improve hole mobility. Herein, a noncovalent conformational locking via S–O secondary interaction is exploited in a phenanthrocarbazole (PC) based polymeric HTM, PC6, to fix the molecular geometry and significantly reduce reorganization energy. Systematic studies on structurally explicit repeats to targeted polymers reveals that the broad and planar backbone of PC remarkably enhances π–π stacking of adjacent polymers, facilitating intermolecular charge transfer greatly. The inserted "Lewis soft" oxygen atoms passivate the trap sites efficiently at the perovskite/HTM interface and further suppress interfacial recombination. Consequently, a PSC employing PC6 as a dopant‐free HTM offers an excellent power conversion efficiency of 22.2 % and significantly improved longevity, rendering it as one of the best PSCs based on dopant‐free HTMs. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) was applied extensively to probe the phase separation and spin relaxation mechanism in the perovskite manganites. In this study, we conducted the measurement of EPR for the perovskite manganites (La 0.5 Pr 0.5 ) 0.67 Ca 0.33 MnO 3 . We found that both paramagnetic and ferromagnetic resonance peaks simultaneously emerged on resonance spectrum near below T C , exhibiting a typical characteristic of phase separation. The linewidth of EPR spectrum progressively enlarged upon the rising of temperature in the temperature range of T > T C and a quasilinear variation of peak-peak width was observed at T C < T < 500 K. In contrast to the usual beliefs that the variation of peak-peak linewidth can be understood either by spin-lattice relaxation or by spin-spin relaxation, however, the linewidth behavior observed here shows a coexistence of two spin relaxation mechanisms. We proposed that the inhomogeneous electronic phases due to the intrinsic self-organizing growth were responsible for the appearance of multiple spin exchange interactions and variational relaxation mechanism. This finding would be possible to pave a new way for further investigating magnetic correlations and spin dynamics in the paramagnetic hole-doped manganites. [ABSTRACT FROM AUTHOR]

Dielectric relaxation in ABO3 perovskite oxides can result from many different charge carrier-related phenomena. Despite a strong understanding of dielectric relaxations, a detailed investigation of the relationship between the content of oxygen vacancies (VO) and dielectric relaxation has not been performed in perovskite oxide films. In this work, we report a systematic investigation of the influence of the VO concentration on the dielectric relaxation of Eu0.5Ba0.5TiO3-δ epitaxial thin films. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration in Eu0.5Ba0.5TiO3-δ films. We found that dipolar defects created by VO interact with the off-centered Ti ions, which results in the dielectric relaxation in Eu0.5Ba0.5TiO3-δ films. Activation energy gradually increases with the increasing content of VO. The present work significantly extends our understanding of relaxation properties in oxide films. [ABSTRACT FROM AUTHOR]

Polycrystalline La 0.825 Sr 0.175 MnO 3 was prepared by solid state reaction method. It exhibits a ferromagnetic–paramagnetic phase transition at T C ∼ 286 K. The intrinsic magnetic properties were clarified by the scaling theory and the isothermal magnetization measured around T C. Based on the modified Arrott plot, Kouvel–Fisher method and Widom relation, the critical exponents are determined to be β = 0. 308 (7) , γ = 1. 065 (8) , δ = 4. 457 (17). Normalization of the critical exponents shows that the extended exchange interaction decays with J ∼ r − 4. 861 , consistent with Tricritical mean field model. Rhodes–Wohlfarth ratio P C / M S >1 suggests that La 0.825 Sr 0.175 MnO 3 is completely itinerant ferromagnet. [Display omitted] • La 0.825 Sr 0.175 MnO 3 shows FM–PM phase transition at 286 K. • Its critical exponents (β = 0.308, γ = 1.065) were determined by the scaling theory. • Its phase transition belongs to Tricritical mean field model. [ABSTRACT FROM AUTHOR]

A novel Sr 3 Ti 2 O 7 :Eu 3+ red phosphor with double-layered perovskite structure was successfully synthesized by solid-state reaction method using Li + ions as charge compensators. Its crystal structure, morphology and photoluminescence under different calcination temperatures and different compensation styles of Li + were investigated. The phosphor could obtain pure tetragonal perovskite phase with I4/ mmm space group at 1300 °C. Non-stoichiometric (NSC) compensation could keep more Sr 2+ ions to hold the perovskite structure stable for higher doping concentration of Eu 3+ . The emission was dominated by the electric-dipole transition with obvious peak splitting due to two different doping sites with lower symmetry of Sr 2+ . Layered structure provided bigger space to hold more Li + ions and NSC style had bigger advantage on the luminescence enhancement for higher doping concentration. Better excitation matches, higher quantum yield (25.1%, λ ex = 395 nm) and better color rendering properties provided a potential red material for white LEDs. [ABSTRACT FROM AUTHOR]

Series of Eu 3+ substituted Na(Gd 1− x Eu x )MgWO 6 phosphors were successfully synthesized by a EDTA-citric acid complexing method. The crystal structure, doping site, morphology, and luminescent properties under different Eu 3+ concentrations were investigated by XRD, Rietveld refinement, Raman spectra, FTIR, SEM and fluorescence spectra as well as Judd–Ofelt analysis and quenching theory. The phosphors had monoclinic double perovskite structure with space group C2/m , rock-salt ordering of B-site (Mg/W) and layered ordering of A-site (Na/Gd/Eu). The redshift of Raman T 2g (1) mode proved Eu 3+ ions had uniformly substituted into A-site. The rare alternative excitation appeared in phosphors that the charge transfer band (CTB) altered from O–W into O–Eu and the strongest excitation altered from CTB into f – f transition of Eu 3+ . The quenching concentration for hypersensitive 5 D 0 – 7 F 2 transition of Eu 3+ reached up to 50.0 mol%, while both the intensity ratio of 5 D 0 – 7 F 2 / 5 D 0 – 7 F 1 and Judd–Ofelt parameter Ω 2 reached the maximum. These two channels of alternative excitation and delayed concentration quenching dually enhanced the luminescence of NaGdMgWO 6 :Eu 3+ phosphor. It is a potential red material for NUV and blue LED chips. [ABSTRACT FROM AUTHOR]

• Low-cost flexible transparent conductive oxide (TCO) film. • Low-cost, indium-free and flexible perovskite CaVO 3 TCO films grown on mica substrates. • Superior stable optical transparency and electrical conductivity after 105 bending cycles. Transparent conducting oxides (TCOs), such as indium-tin oxide (ITO) and indium gallium zinc oxide (IGZO), are essential components in the design of flexible optoelectronic devices. However, it is still a challenge to prepare low-cost flexible transparent conductive film for achieving the flexible functionality together with high optical transparency and electrical conductivity. Herein, fluorphlogopite (mica) is selected as the bendable and transparent substrate for the fabrication of low-cost perovskite CaVO 3 TCO epitaxial film. Benefitting from thin mica substrate with high Young's modulus of 200 GPa, flexible CaVO 3 TCO epitaxial film exhibits high mechanical stability in terms of electrical conductivity and optical transparency after bending up to 105 cycles. The change of resistance can reflect the bending curvature and strain state. Our results provide a new pathway to design superior mechanical flexibility and stability CaVO 3 TCO films for application in flexible, light-weight, and portable smart optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: Double perovskite (Sr0.98− m Ba m Eu0.02)2Ca(Mo1− n W n )O6 phosphors were successfully synthesized by an improved citrate–EDTA complexing method. The structure evolution and the resulting luminescence variation were systematically investigated by X-ray diffraction with Rietveld structure refinement, Fourier transform infrared spectra, Raman spectra, diffuse reflection spectra and photoluminescence spectra. The increased crystal symmetry and increased lattice parameters were observed from (Sr0.98− m Ba m Eu0.02)2CaMoO6 phosphors. These series of phosphors could be effectively excited by near ultraviolet light and emitted a dominant 594nm (5D0–7F1). The hypersensitive 5D0–7F2 transition (615nm) varied with the changed structure symmetry. The CIE chromaticity coordinates were tuned from (0.642, 0.348) to (0.601, 0.389). The luminescence intensity of W6+ substituted powders was greatly enhanced by the blue shift of charge transition band of (Mo/W)O6 with stable emission color. The composition-optimized Sr2Ca(Mo0.5W0.5)O6:Eu phosphor had the highest luminescence intensity and quantum yield comparing to the commercial red phosphors. [Copyright &y& Elsevier]

Graphical picture represents the distorted orthorhombic perovskite structure of TmFeO 3 (left) and Temperature dependence of the magnetic entropy change (−ΔS M) for TmFeO 3 with different external magnetic field H = 1–6 T (right). • Polycrystalline TmFeO3 successfully synthesized using solid-state reaction route. • The magnetocaloric properties of TmFeO3 have been studied. • Maximal entropy change increases with an increase in the external magnetic field. • RCP increases with increasing the external magnetic field. • TmFeO3 is a potential candidate for energy-efficient magnetic refrigeration applications. We presented the structural, magnetic, and magnetocaloric data for perovskite TmFeO 3. XRD revealed distorted orthorhombic structure (Pbnm) for TmFeO 3. Spin-reorientation transition was confirmed through magnetic susceptibility. −ΔS M(max) is 13.72 Jkg-1 K−1 at the temperature of 85 K under ΔH = 6 T, with the RCP value of 676 J/kg. −ΔS M(max) and RCP values were increased with the applied field, possibly due to the d-f exchange interactions. The magnetic hysteresis cycles are established for different values of temperatures. These properties make it a potential candidate used for magnetic refrigerants. For magnetic refrigeration application, very large refrigeration capacity is also required along with large entropy change value. [ABSTRACT FROM AUTHOR]

Au@Pt@Au core-shell nanoparticles, synthesized through chemical reduction, are utilized to improve the photoelectric performance of perovskite solar cells (PSCs) in which carbon films are used as the counter electrode, and the hole-transporting layer is not used. After a series of experiments, these Au@Pt@Au core-shell nanoparticles are optimized and demonstrate outstanding optical and electrical properties due to their local surface plasmon resonance and scattering effects. PSC devices containing 1 wt.% Au@Pt@Au core-shell nanoparticles have the highest efficiency; this is attributable to their significant light trapping and utilization capabilities, which are the result of the distinctive structure of the nanoparticles. The power conversion efficiency of PSCs, with an optimal content of plasmonic nanoparticles (1 wt.%), increased 8.1%, compared to normal PSCs, which was from 12.4% to 13.4%; their short-circuit current density also increased by 5.4%, from 20.5 mA·cm−2 to 21.6 mA·cm−2. The open-circuit voltages remaining are essentially unchanged. When the number of Au@Pt@Au core-shell nanoparticles in the mesoporous TiO2 layer increases, the photovoltaic parameters of the former shows a downward trend due to the recombination of electrons and holes, as well as the decrease in electron transporting pathways. [ABSTRACT FROM AUTHOR]

The Sr3Ti2O7:Eu3+(5%) red phosphor with double-layered perovskite structure is prepared by ball milling (8 h) of SrCO3, TiO2, and Eu2O3 prior to calcination in air (1000-1300 °C, 2 h). [ABSTRACT FROM AUTHOR]

The six-fold symmetry possessed by the (111) surfaces of perovskite oxides allows the epitaxial growth of novel quantum materials such as topological insulators. The dielectric SrTiO3(111) thin film is an ideal buffer layer, providing the readily tunability of charge density in gate-controlled structures. But the high-quality film growth is challenging due to its strong surface polarity as well as the difficulty of obtaining the chemical stoichiometry. Here we show that the layer-by-layer growth of homoepitaxial SrTiO3(111) thin films can be achieved in molecular beam epitaxy method by keeping the growing surface reconstructed. And the cation stoichiometry is optimized precisely with the reflective high energy electron diffraction as the feedback signal that changes sensitively to the variation of metal concentration during growth. With atomically well-defined surfaces, the SrTiO3(111) films show high dielectric performance with the charge density modulated in the range of 2 × 1013/cm2 with the back gate voltage lower than 0.2 V. Methods of further broadening the range are also discussed. [ABSTRACT FROM AUTHOR]