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Double-perovskite GdBaCo2Ox exhibits remarkable magnetic properties, including half-metallicity, high magnetic anisotropy, and photoinduced magnetic phase transition. While manipulating these properties through cation arrangement is attractive, addressing the thermodynamic stability of the Gd/Ba order necessitates an unconventional synthesis approach. Herein, we report the synthesis of both A-site-ordered and -disordered GdBaCo2O6 films employing a combination of substrate-induced strain and low-temperature topochemical oxidation reactions. Both types of films displayed metallic and ferromagnetic behaviors. Interestingly, the A-site-disordered film exhibited superior magnetization (11.5 μB f.u.−1 at 40 kOe), a higher Curie temperature (TC = 165 K), and lower resistivity compared to the A-site-ordered film (9.5 μB f.u.−1 at 40 kOe; TC = 115 K). Theoretical calculations predicted that the alterations in the magnetic and conductive properties of the A-site-disordered film stem from a change in its Co spin states associated with a change in ion arrangement. This mechanism diverges from conventional double perovskites, where magnetic properties primarily stem from alterations in the combination of nearest-neighbor magnetic elements or lattice parameters without affecting the spin state. Our results highlight the potential of unconventional synthesis strategies in broadening the tunability of functionalities in double-perovskite materials and manipulating spin states through cation-placement control. [ABSTRACT FROM AUTHOR]

Mn2Mo3O8 is a layered multiferroic material that exhibits unique properties such as two-dimensional magnetism, room-temperature ferroelectric order, and strong magnetoelectric coupling. However, it has a low magnetic transition temperature (TN) of 41 K. Therefore, in this study, we grain engineered polar-axis-oriented Mn2Mo3O8 epitaxial films to enhance the TN. Mn2Mo3O8 films were grown on yttria-stabilized zirconia (111) substrates. These films consisted of two types of hexagonal grains (G1 and G2) that were oriented at an angle of 30° with respect to each other while maintaining the ferroelectric polar axis of the film along the out-of-plane direction. Such a dual grain system is a result of the layered structure of Mn2Mo3O8, in which the Mn and Mo layers are alternately stacked along the polar axis. The volume fraction of G2 was significantly affected by the film thickness and varied widely in the range 2–48%. Importantly, TN of the grain engineered Mn2Mo3O8 films increased to 163 K with increasing the volume fraction. We speculate that this increase in TN is due to the formation of a three-dimensional magnetic network at the grain boundaries. [ABSTRACT FROM AUTHOR]

Ferroic oxides often exhibit exotic behavior, accompanied by phase transitions. Hexagonal rare-earth iron oxides (h-RFeO3), a promising multiferroic system, have been reported to exhibit ferroelectricity (FE) when the lattice parameter ratio (c/a) exceeds 1.93 and antiferroelectricity (AFE) when c/a is equal to 1.89. Although the AFE–FE phase boundary in the h-RFeO3 systems is assumed to exist at c/a ≈ 1.9, the phase transition has not been observed so far due to the lack of samples with such a c/a ratio. In this study, we show the AFE–FE phase transition in h-RFeO3 films, where R = Dy. We fabricated h-DyFeO3 films with c/a ratios of 1.90–1.92 by controlling the film thicknesses. The h-DyFeO3 films with a c/a ratio of 1.91 exhibited AFE at temperatures below 200 K and FE at temperatures up to 300 K. The phase transition temperature (Tp) was modulated by the c/a ratio. The films also underwent an AFE–FE phase transition upon adjusting the frequency of the voltage applied at the Tp. We discuss the possible origin of the AFE–FE phase transition from the viewpoint of the migration length of the FE domain wall motion. [ABSTRACT FROM AUTHOR]

We fabricated layered-perovskite Sr2IrO4−xF2x thin films by combining pulsed-laser deposition with topotactic fluorination and investigated their structures, electronic states, and electron transport properties. In the fluorination process, the insertion of fluorine into SrO rock-salt layers and the partial removal of oxygen occurred simultaneously while keeping Ir4+. The fluorine amount was evaluated to be 2x ≈ 3, which was much larger than the bulk value. Optical and photoemission measurements revealed that the effective total angular momentum Jeff = 3/2 is stabilized upon fluorination owing to the large electronegativity of fluorine. The Sr2IrO4−xF2x film exhibited a semiconducting behavior described by Efros–Shklovskii variable-range hopping with ρ(T) ≈ T−1/2. These results will be useful for modifying electronic states by anion doping to explore unprecedented physical properties in Ruddlesden–Popper-type iridates. [ABSTRACT FROM AUTHOR]

We report a series of layered superconductors, anti-ThCr2Si2-type RE2O2Bi (RE = rare earth), composed of electrically conductive Bi square nets and magnetic insulating RE2O2 layers. Superconductivity was induced by separating the Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in RE2O2 layers. Intriguingly, the transition temperature of all RE2O2Bi including nonmagnetic Y2O2Bi was approximately scaled by unit cell tetragonality (c/a), implying a key role in the relative separation of the Bi square nets to induce superconductivity. [ABSTRACT FROM AUTHOR]

Topochemical reactions between CaCrO3 and polyvinylidene difluoride yield the new fluorinated phase CaCrO2.5F0.5, which was characterized by powder synchrotron X-ray diffraction, X-ray photoemission spectroscopy, and magnetic susceptibility measurements. The reaction proceeds via reduced oxide intermediates, CaCrO2.67 and CaCrO2.5, in which CrO6 octahedral and CrO4 tetrahedral layers are stacked in a different manner along the c axis of CaCrO3. These two intermediate phases can be selectively synthesized by the carbothermal reduction with g-C3N4. Both CaCrO3 and CaCrO2.5F0.5 adopt the same orthorhombic space group, Pbnm; however, the fluorinated phase has decreased Cr–O–Cr bond angles as compared to the parent compound in both the ab plane and along the c-direction, which indicates an increased orthorhombic distortion due to the fluorination. While the oxygen vacancies are ordered in both intermediate phases, CaCrO2.67 and CaCrO2.5, a site preference for fluorine in the oxyfluoride phase cannot be confirmed. CaCrO3 and CaCrO2.5F0.5 undergo antiferromagnetic phase transitions involving spin canting, where the fluorination causes the transition temperature to increase from 90 K to 110 K, as a result of the competition between the increased octahedral tilting and the enhancement of superexchange interactions involving Cr3+ ions in the CaCrO2.5F0.5 structure. [ABSTRACT FROM AUTHOR]

Aurivillius-type oxyfluorides are promising ferroelectric and photocatalytic materials. However, their thin films have yet to be fabricated because of the difficulty of synthesis when using both conventional high-temperature gas-phase processes and low-temperature topotactic methods. Here, we present reactive solid phase epitaxy of a layered Aurivillius-type oxyfluoride Bi2TiO4F2 from room-temperature fabricated Bi2TiOx using polyvinylidene fluoride (PVDF) as a fluorine source. Bi2TiO4F2 epitaxial films are obtained by reacting a room-temperature fabricated precursor with PVDF at 330 °C under an Ar flow. However, crystallization does not proceed through PVDF treatment in air, indicating that a reduced atmosphere is crucial to removing oxide ions from the precursor and incorporating fluoride ions. The Bi2TiO4F2 film shows a peak at 240 K in the dielectric constant-versus-temperature curve, which originates from the tilting of Ti(O,F)6 octahedra. This peak temperature is lower than that of the bulk (284 K), suggesting that the local structural distortion is suppressed because of the epitaxial strain from the substrate. Reactive solid phase epitaxy using PVDF as described in this paper should provide a new means of synthesizing transition-metal oxyfluorides in the epitaxial thin-film form. [ABSTRACT FROM AUTHOR]

We demonstrated selective fluorination of a SrFeO2.5 layer in a SrFeO2.5/SrRuO3 epitaxial bilayer film via a topotactic reaction with polyvinylidene difluoride while maintaining the epitaxial relationship. Physical property measurements of the SrFeO2F/SrRuO3 heterostructure confirmed that the SrRuO3 layer could work as a good bottom electrode. [ABSTRACT FROM AUTHOR]

Herein, we investigated the domain morphologies of defect-perovskite LaCuOx (2.5 ≤x≤ 3.0) thin films grown on cubic SrTiO3 (100) and orthorhombic NdGaO3 (110) substrates by pulsed-laser deposition. Both films were composed of narrow rectangular-shaped domains, which extended in the [001] direction of LaCuOx. The LaCuOx film grown on SrTiO3 showed a labyrinth-like domain pattern composed of 90° domains, whereas the film on NdGaO3 displayed a stripe pattern with 180° domains. Furthermore, we observed anisotropy in the resistivity; the resistivity along the length of the domains was about three times lower than that across their width. This indicated that the domain boundaries behaved as carrier scattering centers. [ABSTRACT FROM AUTHOR]

A-site cation-ordered perovskite cobaltite, RBaCo2Ox (R = rare earth element), exhibits fascinating physical properties, such as spin-state ordering and high oxygen conductivity, because of the large tetragonal distortion of the Co orbital. However, the distorted coordination geometry prefers oxygen vacancies, resulting in a difficulty in obtaining the stoichiometric phase (x = 6). For example, x in YBaCo2Ox, which has largely distorted Co orbitals because of the small size of Y3+, has so far been limited to 5.52. To expand the available range of x, in this study, we performed a low-temperature topotactic oxidation of YBaCo2O5.3 epitaxial films using a strong oxidizing agent NaClO. The x value can be varied in a wide range of 5.3–6.0, maintaining the A-site cation-ordered perovskite structure, by changing the pH and temperature of NaClO. The single crystalline film with x = 6 exhibits large tetragonal distortion (c/a = 0.968) because of the small ionic radius of Y3+ and substrate-induced tensile strain. Unlike antiferromagnetic insulating YBaCo2O5.5, the fully oxidized film with x = 6 exhibits in-plane ferromagnetism and metallicity with a Curie temperature of 130 K possibly because of the double-exchange interaction between Co3+ and Co4+. Moreover, the YBaCo2O6 film exhibits huge magnetic anisotropy with a magnetic anisotropy constant of 1.5 × 108 erg cm−3, demonstrating that the A-site cation-ordered perovskite structure is promising for obtaining high magnetocrystalline anisotropic materials. [ABSTRACT FROM AUTHOR]

This study reports improved performance of inverted organic solar cells by using high working-pressure sputtered ZnO. Sputtering produces highly crystalline ZnO without the need for thermal annealing. However, photovoltaic devices fabricated by using sputtered ZnO have shown lower power conversion efficiencies than those made by using sol–gel ZnO. On the other hand, sol–gel ZnO limits the flexible application of inverted organic solar cells because of high-temperature annealing. Therefore, a new method of sputtering under high working pressure is developed. The power conversion efficiency of inverted organic solar cells fabricated using this high working-pressure-sputtered ZnO (η = 8.6%, VOC = 0.77 V, JSC = 15.6 mA cm−2, and FF = 0.72) is superior to that of conventional sol–gel ZnO-based devices (η = 7.8%, VOC = 0.73 V, JSC = 16.0 mA cm−2, and FF = 0.63). Furthermore, utilizing the low temperature process of sputtering, flexible application is successfully achieved using polyethylene terephthalate indium tin oxide films. [ABSTRACT FROM AUTHOR]

Porous organic salt (POS) crystals composed of 9-(4-sulfophenyl)anthracene (SPA) and triphenylmethylamine (TPMA) were impregnated with fullerenes (C60 and C70), which were arranged in one dimensional close contact. POS crystals of SPA and TPMA without fullerenes exhibit blue fluorescence due to SPA, whereas the fluorescence was quenched in POS with fullerenes due to electron transfer from the singlet excited state of SPA to fullerenes. [ABSTRACT FROM AUTHOR]

Multiple photosynthetic reaction centres have been successfully constructed using strong supramolecular complexes of free base porphyrin polypeptides with lithium ion-encapsulated C60 (Li+@C60) as compared with those of C60. Efficient energy migration and electron transfer occur in the supramolecular complexes. [ABSTRACT FROM AUTHOR]

We report a series of layered superconductors, anti-ThCr 2 Si 2 -type RE 2 O 2 Bi (RE = rare earth), composed of electrically conductive Bi square nets and magnetic insulating RE 2 O 2 layers. Superconductivity was induced by separating the Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in RE 2 O 2 layers. Intriguingly, the transition temperature of all RE 2 O 2 Bi including nonmagnetic Y 2 O 2 Bi was approximately scaled by unit cell tetragonality (c/a), implying a key role in the relative separation of the Bi square nets to induce superconductivity.

Topochemical reactions between CaCrO3 and polyvinylidene difluoride yield the new fluorinated phase CaCrO2.5F0.5, which was characterized by powder synchrotron X-ray diffraction, X-ray photoemission spectroscopy, and magnetic susceptibility measurements. The reaction proceeds via reduced oxide intermediates, CaCrO2.67 and CaCrO2.5, in which CrO6 octahedral and CrO4 tetrahedral layers are stacked in a different manner along the c axis of CaCrO3. These two intermediate phases can be selectively synthesized by the carbothermal reduction with g-C3N4. Both CaCrO3 and CaCrO2.5F0.5 adopt the same orthorhombic space group, Pbnm; however, the fluorinated phase has decreased Cr-O-Cr bond angles as compared to the parent compound in both the ab plane and along the c-direction, which indicates an increased orthorhombic distortion due to the fluorination. While the oxygen vacancies are ordered in both intermediate phases, CaCrO2.67 and CaCrO2.5, a site preference for fluorine in the oxyfluoride phase cannot be confirmed. CaCrO3 and CaCrO2.5F0.5 undergo antiferromagnetic phase transitions involving spin canting, where the fluorination causes the transition temperature to increase from 90 K to 110 K, as a result of the competition between the increased octahedral tilting and the enhancement of superexchange interactions involving Cr3+ ions in the CaCrO2.5F0.5 structure.

Aurivillius-type oxyfluorides are promising ferroelectric and photocatalytic materials. However, their thin films have yet to be fabricated because of the difficulty of synthesis when using both conventional high-temperature gas-phase processes and low-temperature topotactic methods. Here, we present reactive solid phase epitaxy of a layered Aurivillius-type oxyfluoride Bi2TiO4F2 from room-temperature fabricated Bi2TiOx using polyvinylidene fluoride (PVDF) as a fluorine source. Bi2TiO4F2 epitaxial films are obtained by reacting a room-temperature fabricated precursor with PVDF at 330 °C under an Ar flow. However, crystallization does not proceed through PVDF treatment in air, indicating that a reduced atmosphere is crucial to removing oxide ions from the precursor and incorporating fluoride ions. The Bi2TiO4F2 film shows a peak at 240 K in the dielectric constant-versus-temperature curve, which originates from the tilting of Ti(O,F)6 octahedra. This peak temperature is lower than that of the bulk (284 K), suggesting that the local structural distortion is suppressed because of the epitaxial strain from the substrate. Reactive solid phase epitaxy using PVDF as described in this paper should provide a new means of synthesizing transition-metal oxyfluorides in the epitaxial thin-film form.

Multiple photosynthetic reaction centres have been successfully constructed using strong supramolecular complexes of free base porphyrin polypeptides with lithium ion-encapsulated C60 (Li(+)@C60) as compared with those of C60. Efficient energy migration and electron transfer occur in the supramolecular complexes.