Showing papers on "Perovskite (structure) published in 2011"
TL;DR: The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an eg symmetry of surface transition metal cations in an oxide.
Abstract: The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–δ (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an e g symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an e g occupancy close to unity, with high covalency of transition metal–oxygen bonds.
3,876 citations
TL;DR: Perovskite QD-sensitized 3.6 μm-thick TiO(2) film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm(-2)), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.
Abstract: Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2–3 nm sized perovskite (CH3NH3)PbI3 nanocrystal. Spin-coating of the equimolar mixture of CH3NH3I and PbI2 in γ-butyrolactone solution (perovskite precursor solution) leads to (CH3NH3)PbI3 quantum dots (QDs) on nanocrystalline TiO2 surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO2 film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm−2), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.
2,781 citations
TL;DR: The introduction of the Cl(-) anion in the borate systems generates a new perovskite-like phase, K(3)B(6)O(10)Cl, which exhibits a large second harmonic response, about four times that of KH(2)PO(4) (KDP), and is transparent from the deep UV (180 nm) to middle-IR region.
Abstract: Introduction of the Cl- anion in the borate systems generates a new perovskite-like phase, K3B6O10Cl, which exhibits a large second harmonic response, about four times that of KH 2PO4 (KDP), and is transparent from the deep UV (180 nm) to middle-IR region. K3B6O10Cl crystallizes in the noncentrosymmetric and rhombohedral space group R3m. The structure consists of the A-site hexaborate [B6O10] groups and the BX 3 Cl-centered octahedral [ClK6] groups linked together through vertices to form the perovskite framework represented by ABX 3.
574 citations
TL;DR: It is reported that colossal negative thermal expansion (defined as linear expansion <−10−4 K−1 over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions.
Abstract: The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <-10(-4) K(-1) over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO(3) shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi(0.95)La(0.05)NiO(3) is -137×10(-6) K(-1) and a value of -82×10(-6) K(-1) is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders.
341 citations
TL;DR: The present study shows that artificial hole doping indeed enhances the conductivity of a metal-halide cubic perovskite, and is suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure.
Abstract: The structural and electrical properties of a metal-halide cubic perovskite, CH3NH3SnI3, have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity.
333 citations
TL;DR: In this paper, the effect of doping on the electric and magnetic properties of BiFeO3 perovskite has been summarized and a review of recent studies on doped biFeOO3 ceramics is presented.
Abstract: BiFeO3, the paradigm of single-phase multiferroic materials, has potential applications in information storage, sensors and actuators This perovskite has a rhombohedral R3c crystallographic structure and shows a spin-modulated cycloidal magnetic structure with a modulation period of ∼62 nm It reveals magnetoelectric coupling at room temperature However, its low remanent magnetization and relatively important leakage current are the main limitations for possible applications In this review we summarize recent studies on doped BiFeO3 Special attention is put on obtaining and sintering bulk BiFeO3 ceramics and the effect of doping on the electric and magnetic properties
229 citations
TL;DR: Investigation of the representative compounds SrMO(2)N (M = Nb, Ta) using neutron and electron diffraction revealed a robust 1O/2(O(0.5)N( 0.5)) partial anion order that directs the rotations of MO(4)N.(2) octahedra in the room-temperature superstructure.
Abstract: Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide–nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO2N (M = Nb, Ta) using neutron and electron diffraction. This revealed a robust 1O/2(O0.5N0.5) partial anion order (up to at least 750 °C in the apparently cubic high-temperature phases) that directs the rotations of MO4N2 octahedra in the room-temperature superstructure. The anion distribution is consistent with local cis-ordering of the two nitrides in each octahedron driven by covalency, which results in disordered zigzag M–N chains in planes within the perovskite lattice. Local structures for the full range of oxynitride perovskites are predicted and a future challenge is to tune properties by controlling the order and dimensionality of the anion chains and networks. Oxynitrides of transition metals are emerging materials with useful properties and improved stability over corresponding nitrides, but a full understanding of their anion ordering has been lacking. Now, a neutron and electron diffraction study of the perovskites SrNbO2N and SrTaO2N reveals the chemical principles for anion order and their potential influence on materials properties.
216 citations
TL;DR: The oxynitride CaNbO₂N, was found to be active for hydrogen and oxygen evolution from methanol and aqueous AgNO₃, respectively, even under irradiation by light at long wavelengths (λ<560 nm).
Abstract: Photocatalytic activities of perovskite-type niobium oxynitrides (CaNbO2N, SrNbO2N, BaNbO2N, and LaNbON2) were examined for hydrogen and oxygen evolution from water under visible-light irradiation. These niobium oxynitrides were prepared by heating the corresponding oxide precursors, which were synthesized using the polymerized complex method, for 15 h under a flow of ammonia. They possess visible-light absorption bands between 600–750 nm, depending on the A-site cations in the structures. The oxynitride CaNbO2N, was found to be active for hydrogen and oxygen evolution from methanol and aqueous AgNO3, respectively, even under irradiation by light at long wavelengths (λ<560 nm). The nitridation temperature dependence of CaNbO2N was investigated and 1023 K was found to be the optimal temperature. At lower temperatures, the oxynitride phase is not adequately produced, whereas higher temperatures produce more reduced niobium species (e. g., Nb3+ and Nb4+), which can act as electron-hole recombination centers, resulting in a decrease in activity.
212 citations
TL;DR: High-frequency EPR spectrometers and pulsed EPR techniques such as the hyperfine sublevel correlation experiment (HYSCORE) may now routinely be used for dedicated investigations, providing considerably more insight than the application of standard continuous-wave EPR.
Abstract: Multi-frequency and pulsed electron paramagnetic resonance (EPR) provides a sensitive spectroscopic tool to elucidate the defect structure of transition-metal doped perovskite oxides, as well as to monitor dynamic processes of oxygen vacancies in these materials. In this regard, high-frequency EPR spectrometers and pulsed EPR techniques such as the hyperfine sublevel correlation experiment (HYSCORE) may now routinely be used for dedicated investigations, providing considerably more insight than the application of standard continuous-wave EPR. Recent results include the formation of defect complexes between acceptor-type transition-metal centers with either one or two oxygen vacancies for the reason of charge compensation. Furthermore, such defect complexes follow the domain switching upon poling ferroelectric compounds with correspondingly high electric fields. On the other hand, multi-valent manganese functional centers provide trapping centers for electronic and ionic charge carriers (e', ) such that valency altered acceptor states or defect complexes are formed. Additionally, the trapping of charge carriers at the intrinsic 'reduced' B-site ions, and , can be observed by means of EPR spectroscopy.
198 citations
TL;DR: In this article, a small amount of secondary phase on a (001) La0.8Sr0.2CoO3−δ (LSC) surface can either significantly activate or passivate the electrode.
Abstract: Surface-decoration of perovskites can strongly affect the oxygen reduction activity, and therefore is a new and promising approach to improve SOFC cathode materials. In this study, we demonstrate that a small amount of secondary phase on a (001) La0.8Sr0.2CoO3−δ (LSC) surface can either significantly activate or passivate the electrode. LSC (001) microelectrodes prepared by pulsed laser deposition on a (001)-oriented yttria-stabilized zirconia (YSZ) substrate were decorated with La-, Co-, and Sr-(hydr)oxides/carbonates. “Sr”-decoration with nanoparticle coverage in the range from 50% to 80% of the LSC surface enhanced the surface exchange coefficient, kq, by an order of magnitude while “La”-decoration and “Co”-decoration led to no change and reduction in kq, respectively. Although the physical origin for the enhancement is not fully understood, results from atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy suggest that the observed kq enhancement for “Sr”-decorated surfaces can be attributed largely to catalytically active interface regions between surface Sr-enriched particles and the LSC surface.
192 citations
TL;DR: In this article, the effects of Bi nonstoichiometry on (Bi0.5+xNa)TiO3 (BNT) ceramics were investigated at x=−1−+2
Abstract: Effects of Bi nonstoichiometry on (Bi0.5+xNa)TiO3 (BNT) ceramics were investigated at x=−1–+2 mol % of Bi0.5 covering Bi deficiency and excess. At all compositions, rhombohedrally symmetric BNT perovskite formed without secondary phases. Increasing x caused smaller grains. Higher piezoelectric coefficient (d33) but lower depolarization temperature (Td) occurred at Bi excess than at Bi deficiency and vice versa. Leakage current at room temperature decreased with decreasing x. Electrical conductivity of the stoichiometric BNT (x=0) from 700 to 900 °C increased with decreasing partial oxygen pressure from 1 to 10−5 atm suggesting n-type conductivity at elevated temperatures.
TL;DR: In this article, specific heat and 1H NMR measurements have been used to study the phase transition in the metal-organic framework (MOF) compound [(CH3)2NH2]Zn(HCOO)3], which possesses a perovskite-type architecture, undergoing a remarkable order-disorder phase transition at 156 K.
Abstract: Transitions associated with orientational order–disorder phenomena are found in a wide range of materials and may have a significant impact on their properties. In this work, specific heat and 1H NMR measurements have been used to study the phase transition in the metal-organic framework (MOF) compound [(CH3)2NH2]Zn(HCOO)3. This compound, which possesses a perovskite-type architecture, undergoes a remarkable order–disorder phase transition at 156 K. The (DMA+) cationic moieties that are bound by hydrogen bonds to the oxygens of the formate groups (N─H⋯O ∼ 2.9 A) are essentially trapped inside the basic perovskite cage architecture. Above 156 K, it is the orientations of these moieties that are responsible for the disorder, as each can take up three different orientations with equal probability. Below 156 K, the DMA+ is ordered within one of these sites, although the moiety still retains a considerable state of motion. Below 40 K, the rotational motions of the methyl groups start to freeze. As the temperature is increased from 4 K in the NMR measurements, different relaxation pathways can be observed in the temperature range approximately 65–150 K, as a result of a “memory effect.” This dynamic behavior is characteristic of a glass in which multiple states possess similar energies, found here for a MOF. This conclusion is strongly supported by the specific heat data.
TL;DR: The ground state of (Mg,Fe)(Si,Fe)O(3) perovskite, the major mineral phase in Earth's lower mantle, has high-spin ferric iron at both dodecahedral (A) and octahedral (B) sites, suggesting a possible source of seismic-velocity anomalies in the lower mantle.
Abstract: Using density functional theory plus Hubbard U calculations, we show that the ground state of (Mg,Fe)(Si,Fe)O(3) perovskite, the major mineral phase in Earth's lower mantle, has high-spin ferric iron (S=5/2) at both dodecahedral (A) and octahedral (B) sites. With increasing pressure, the B-site iron undergoes a spin-state crossover to the low-spin state (S=1/2) between 40 and 70 GPa, while the A-site iron remains in the high-spin state. This B-site spin-state crossover is accompanied by a noticeable volume reduction and an increase in quadrupole splitting, consistent with recent x-ray diffraction and Mossbauer spectroscopy measurements. The anomalous volume reduction leads to a significant softening in bulk modulus during the crossover, suggesting a possible source of seismic-velocity anomalies in the lower mantle.
TL;DR: A large-size single crystal of nearly stoichiometric SrCoO(3) was prepared with a two-step method combining the floating-zone technique and subsequent high oxygen pressure treatment, indicative of the possible effect of orbital fluctuation in the intermediate spin ferromagnetic metallic state.
Abstract: A large-size single crystal of nearly stoichiometric SrCoO(3) was prepared with a two-step method combining the floating-zone technique and subsequent high oxygen pressure treatment. SrCoO(3) crystallizes in a cubic perovskite structure with space group Pm3m, and displays an itinerant ferromagnetic behavior with the Curie temperature of 305 K. The easy magnetization axis is found to be along the [111] direction, and the saturation moment is 2.5 µ(B)/f.u., in accord with the picture of the intermediate spin state. The resistivity at low temperatures (T) is proportional to T(2), indicative of the possible effect of orbital fluctuation in the intermediate spin ferromagnetic metallic state. Unusual anisotropic magnetoresistance is also observed and its possible origin is discussed.
TL;DR: In this paper, a mixed conducting perovskite materials system, SrTi1-xFexO3-δ, is selected, offering the ability to systematically control both the levels of ionic and electronic conductivity as well as the energy band structure.
Abstract: Identifying the important factors governing the oxygen reduction kinetics at solid oxide fuel cell cathodes is critical for enhanced performance, particularly at reduced temperatures. In this work, a model mixed conducting perovskite materials system, SrTi1–xFexO3–δ, is selected, offering the ability to systematically control both the levels of ionic and electronic conductivity as well as the energy band structure. This, in combination with considerably simplified electrode geometry, serves to demonstrate that the rate of oxygen exchange at the surface of SrTi1–xFexO3–δ is only weakly correlated with either high electronic or ionic conductivity, in apparent contradiction with common expectations. Based on the correlation found between the position of the Fermi energy relative to the conduction band edge and the activation energy exhibited by the exchange rate constant, it is possible to confirm experimentally, for the first time, the key role that the minority electronic species play in determining the overall reaction kinetics. These observations lead to a new conceptual model describing cathode kinetics and provide guidelines for identifying cathodes with improved performance.
TL;DR: The reversibility of the semiconducting-to-metallic transitions of the electronic structure discovered here, coupled to the strain state and temperature, underscores the necessity of in situ investigations on SOFC cathode material surfaces.
Abstract: In-depth probing of the surface electronic structure on solid oxide fuel cell (SOFC) cathodes, considering the effects of high temperature, oxygen pressure, and material strain state, is essential toward advancing our understanding of the oxygen reduction activity on them. Here, we report the surface structure, chemical state, and electronic structure of a model transition metal perovskite oxide system, strained La0.8Sr0.2CoO3 (LSC) thin films, as a function of temperature up to 450 °C in oxygen partial pressure of 10–3 mbar. Both the tensile and the compressively strained LSC film surfaces transition from a semiconducting state with an energy gap of 0.8–1.5 eV at room temperature to a metallic-like state with no energy gap at 200–300 °C, as identified by in situ scanning tunneling spectroscopy. The tensile strained LSC surface exhibits a more enhanced electronic density of states (DOS) near the Fermi level following this transition, indicating a more highly active surface for electron transfer in oxygen ...
TL;DR: In this paper, BaTiO3 and Bi(Mg1/2Ti 1/2)O3 polycrystalline ceramics were obtained via solid-state processing techniques.
Abstract: (1−x)BaTiO3–xBi(Mg1/2Ti1/2)O3 [(1−x)BT–xBMT] polycrystalline ceramics were obtained via solid-state processing techniques. The solubility limit for (1−x)BT–xBMT was determined to be about x=0.07. A systematic structural change from the ferroelectric tetragonal phase to pseudocubic phase was observed at about x≥0.05 at room temperature. Dielectric measurements revealed a gradual change from normal ferroelectric of pure BaTiO3 to highly dispersive relaxor-like characteristics in the solid solution with 30–60 mol% Bi(Mg1/2Ti1/2)O3, showing low-temperature coefficients of capacitance over a wide temperature range. The properties of Nb2O5-doped 0.85BT–0.15BMT ceramics were investigated to better understand the formation mechanism of core-shell structure, for further improving the temperature stability of the dielectric behavior.
TL;DR: The results imply that the emission from substituted Er3+ ions may be used as a structural probe for the ferroelectric titanates.
Abstract: Upconversion photoluminescence (PL) of Er3+-doped BaTiO3 (BTO) with perovskite ABO3 structure is studied in terms of Er3+ substitutions for Ba (A-) and Ti (B-site) with different Er3+ doping concentrations. PL quenching with an increase Er3+ doping concentration is investigated based on the structural change and energy transfer of cross-relaxation process in BTO: Er, i.e. 2H11/2 + 4I15/2→4I9/2 + 4I13/2. Temperature dependence of the PL in BTO: Er is revealed, which is associated with phase transitions of BTO host. The results imply that the emission from substituted Er3+ ions may be used as a structural probe for the ferroelectric titanates.
TL;DR: The cubic perovskite BaFeO(3) (see picture), which is obtained by a low-temperature reaction using ozone as an oxidant, exhibits ferromagnetism with a fairly large moment above a small critical field of approximately 0.3 T.
Abstract: Magnetic attraction: The cubic perovskite BaFeO(3) (see picture, Ba blue, Fe brown, O white), which is obtained by a low-temperature reaction using ozone as an oxidant, exhibits ferromagnetism with a fairly large moment of 3.5 μ(B) per Fe ion above a small critical field of approximately 0.3 T. This specific ferromagnetism is attributed to the enhancement of O→Fe charge transfer that arises from deepening of the Fe(4+) d levels.
TL;DR: In this article, the effects of dopant content on their structural and electrochemical properties including crystalline structure, oxygen nonstoichiometry, stability in presence of CO2, compatibility with electrolytes, thermal expansion coefficient, electrical conductivity, and cathodic interfacial polarization resistance are evaluated as cathode materials for intermediate-temperature solid oxide fuel cells.
TL;DR: Perovskite YFe0.5Cr 0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky-Moriya interaction as discussed by the authors.
Abstract: Perovskite YFe0.5Cr0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky–Moriya interaction. Below a compensation temperature (Tcomp), a tunable bipolar switching of magnetization is demonstrated by changing the magnitude of the field while keeping it in the same direction. The present compound also displays both normal and inverse magnetocaloric effects above and below 260 K, respectively. These phenomena coexisting in a single magnetic system can be tuned in a predictable manner and have potential applications in electromagnetic devices.
TL;DR: In this article, the conventional mixed oxide method (1−x)Bi(Mg 1/2Ti1/2)O3+xBaTiO3 +xBT, x = 0.2−1.4, a bismuth-rich phase was observed beside the perovskite phase, while the tetragonal phases were formed when x ≥ 0.94.
Abstract: By the conventional mixed oxide method (1−x)Bi(Mg1/2Ti1/2)O3–xBaTiO3 ((1−x)BMT–xBT, x = 0.2−1.0) ceramics were prepared. For x ≤ 0.4, a bismuth-rich phase was observed beside the perovskite phase. For 0.5 ≤ x ≤ 0.92 ceramics, all the compositions belong to the pseudocubic phase, while the tetragonal phases were formed when x ≥ 0.94. With the increase of BT content, a change from a relaxor-like behavior to a normal ferroelectric behavior was observed, while the change of Tmax is in the form of “U” curve. Furthermore, stable dielectric permittivity (1500–3000) and low losses (tan δ < 2%) were obtained in the 0.4 ≤ x ≤ 0.6 ceramics in the temperature range 200°C–400°C, indicating a potential for high-temperature applications.
TL;DR: It is demonstrated that the magnetic order suppresses the ferroelectric lattice dilation and increases the soft-phonon energy by ∼50%, indicating the largest magnetoelectric effects yet attained.
Abstract: We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ∼70% and increases the soft-phonon energy by ∼50%, indicating the largest magnetoelectric effects yet attained.
TL;DR: In this article, the first-order displacive phase transitions from the high-temperature nonpolar phase to the low temperature polar (x ≤ 0.125) and antipolar (0.125 ≤ x ≥ 0.25) phases were investigated.
Abstract: Neutron powder diffraction was used to determine changes in the nuclear and magnetic structures of Bi1−xNdxFeO3 polymorphs involved in the first-order displacive phase transitions from the high-temperature nonpolar phase to the low temperature polar (x ≤ 0.125) and antipolar (0.125 ≤ x ≤ 0.25) phases, respectively. The high-temperature phase (O1), which crystallizes with a structure similar to the room-temperature form of NdFeO3, exhibits Pbnm symmetry and unit cell √2ac × √2ac × 2ac (where ac ≈ 4 A is the lattice parameter of an ideal cubic perovskite), determined by a−a−c+ octahedral tilting. The low-temperature polar structure (R) is similar to the β-phase of BiFeO3 and features rhombohedral symmetry determined by a−a−a− octahedral rotations and cation displacements. The recently discovered antipolar phase (O2) resembles the antiferroelectric Pbam (√2ac × 2√2ac × 2ac) structure of PbZrO3 but with additional displacements that double the PbZrO3 unit cell along the c-axis to √2ac × 2√2ac × 4ac and yield ...
TL;DR: In this article, the existence of spontaneous magnetization in Mn-doped polycrystalline BaTiO3 thin films was shown to be inconsistent with the presence of ferroelectricity.
Abstract: Single-phase perovskite 5 at. % Mn-doped and undoped polycrystalline BaTiO3 thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO3, Mn-doped BaTiO3 reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure and is attributed to the formation of bound magnetic polarons (BMPs). This BMP formation is enhanced by oxygen vacancies. The present work confirms a theoretical work from C. Ederer and N. Spaldin on ferroelectric perovskites [Nature Mat. 3, 849 (2004)] that shows that the existence of ferroelectricity is incompatible with the existence of a spontaneous magnetization in Mn-doped BaTiO3 thin films.
TL;DR: This work demonstrates a perovskite heteroepitaxial metal-base transistor operating at room temperature, enabled by interface dipole engineering, which provides a platform for incorporating the exotic ground states of perovkite oxides, as well as novel electronic phases at their interfaces.
Abstract: 'More than Moore' captures a concept for overcoming limitations in silicon electronics by incorporating new functionalities in the constituent materials. Perovskite oxides are candidates because of their vast array of physical properties in a common structure. They also enable new electronic devices based on strongly-correlated electrons. The field effect transistor and its derivatives have been the principal oxide devices investigated thus far, but another option is available in a different geometry: if the current is perpendicular to the interface, the strong internal electric fields generated at back-to-back heterojunctions can be used for oxide electronics, analogous to bipolar transistors. Here we demonstrate a perovskite heteroepitaxial metal-base transistor operating at room temperature, enabled by interface dipole engineering. Analysis of many devices quantifies the evolution from hot-electron to permeable-base behaviour. This device provides a platform for incorporating the exotic ground states of perovskite oxides, as well as novel electronic phases at their interfaces.
TL;DR: In this paper, the existence of spontaneous magnetization in Mn-doped polycrystalline BaTiO3 thin films was shown to be inconsistent with the presence of ferroelectricity.
Abstract: Single-phase perovskite 5 at.% Mn-doped and undoped polycrystalline BaTiO3 thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO3, Mn-doped BaTiO3 reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure and is attributed to the formation of bound magnetic polarons (BMPs). This BMP formation is enhanced by oxygen vacancies. The present work confirms a theoretical work from C. Ederer and N. Spaldin on ferroelectric perovskites [Nature Mat. 3, 849 (2004)] which shows that the existence of ferroelectricity is incompatible with the existence of a spontaneous magnetization in Mn-doped BaTiO3 thin films.
TL;DR: In this paper, high surface area perovskite-based oxygen carriers, LaCoO3, LaCeCoO 3 and LaMnO3 were synthesized by the reactive grinding method (S. Kaliaguine, A. van Neste, US Pat., 6 017 504, 2000; Applied Catalysis, A, 2001, 209, 345-358).
Abstract: Chemical looping combustion is a novel technique with inherent separation of the greenhouse gas CO2 from atmospheric nitrogen in combustion of gaseous fuels. The selection of a suitable oxygen carrier which circulates between two fluidized bed reactors is a key issue for the performance of this technology. In this work, high surface area perovskite-based oxygen carriers, LaCoO3, LaCeCoO3 and LaMnO3, were synthesized by the reactive grinding method (S. Kaliaguine, A. van Neste, US Pat., 6 017 504, 2000; Applied Catalysis, A, 2001, 209, 345-358). LaMnO3 was also prepared by another method designated as nanocasting. The perovskites were characterized using different methods such as XRD, SEM, N2 adsorption, H2-TPR, TPD-O2 and finally the reactivity and stability of the carrier materials were tested in a CREC fluidized riser simulator using multiple reduction–oxidation cycles under two conditions: with low and high amount of CH4 (0.5 and 10 ml) as a feed. It was found from TPD-O2 and H2-TPR studies that the LaMnO3 perovskite, particularly the one prepared by the nanocasting method (LaMn-NC), has a high amount of available α-O2 (surface oxygens) and high density of surface anion vacancies. Moreover, the Mn-based perovskites showed easier reducibility compared to the Co-based oxygen carriers. The results obtained under two different conditions of CH4 pressure confirmed the strong dependency of the CLC results on this factor. Higher stability and no CO formation during the multiple redox cycles were indeed observed while using low pressure of CH4. Higher reactivity of the carriers was however obtained while using higher CH4 pressure but CO was detected in the products in this case. The higher reactivity of Mn-based perovskites could not only be due to the higher amount of surface oxygen and reducible sites present in the sample but also to the higher specific surface area of the perovskite. The formation of lanthanum and manganese silicate was observed for LaMn-NC which could be the reason for the reduction in CH4 conversion observed between the eighth and tenth redox cycles. This compound could be as a result of interaction between remnant silica in the sample with La and Mn from the perovskite lattice. No coke formation was detected on the oxygen carriers however, some agglomeration of the particles occurred, as confirmed by SEM images, XRD data and N2 sorption tests. Furthermore, XRD patterns confirmed that the structure of all perovskites remained unchanged after multiple redox cycles.