Although known since the late 19th century, organic–inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic–inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.

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Optical Response of High-Dielectric-Constant Perovskite-Related Oxide

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

Synthesis of multifunctional magnetic nanoparticles (MFMNPs) is one of the most active research areas in advanced materials. MFMNPs that have magnetic properties and other functionalities have been demonstrated to show great promise as multimodality imaging probes. Their multifunctional surfaces also allow rational conjugations of biological and drug molecules, making it possible to achieve target-specific diagnostics and therapeutics. This review first outlines the synthesis of MNPs of metal oxides and alloys and then focuses on recent developments in the fabrication of MFMNPs of core/shell, dumbbell, and composite hybrid type. It also summarizes the general strategies applied for NP surface functionalization. The review further highlights some exciting examples of these MFMNPs for multimodality imaging and for target-specific drug/gene delivery applications.

Synthesis, Functionalization, and Biomedical Applications of Multifunctional Magnetic Nanoparticles

Extraordinary electron systems can be generated at well-defined interfaces between complex oxides. In recent years, progress has been achieved in exploring and making use of the fundamental properties of such interfaces, and it has become clear that these electron systems offer the potential for possible future devices. We trace the state of the art of this emerging field of electronics and discuss some of the challenges and pitfalls that may lie ahead.

http://science.sciencemag.org/content/sci/327/5973/1607.full.pdf

Oxide Interfaces—An Opportunity for Electronics

We report the first successful preparation of thin films of Y‐Ba‐Cu‐O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.

Preparation of Y‐Ba‐Cu oxide superconductor thin films using pulsed laser evaporation from high Tc bulk material

We report the observation of large low-field magnetoresistance (MR) behavior in ${\mathrm{CaCu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ with a perovskite-related $({\mathrm{AA}}^{\ensuremath{'}}_{3}B_{4}{\mathrm{O}}_{12})$ structure. ${\mathrm{Ca}}^{2+}{\mathrm{Cu}}_{3}^{2+}{\mathrm{Mn}}_{4}^{4+}{\mathrm{O}}_{12}$ is semiconducting and orders ferromagnetically at 355 K. However, it has neither mixed valency of Mn for double-exchange magnetic interactions, nor Jahn-Teller ${\mathrm{Mn}}^{3+}$ ions, nor a metal-insulator transition. The MR smoothly increases with decreasing temperature and is $\ensuremath{-}40%$ at 20 K. The low-field MR response does not show the strong temperature-dependent decay characteristic of the ${\mathrm{LnMnO}}_{3}$ perovskite-based systems and appears consistent with an intergrain-interdomain tunneling origin.

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Large Low-Field Magnetoresistance in Perovskite-type CaCu 3 Mn 4 O 12 without Double Exchange

Double-perovskites Sr2MMoO6 (M = Co, Ni) have been investigated as anode materials for a solid oxide fuel cell. At room temperature, both Sr2CoMoO6 and Sr2NiMoO6 are tetragonal (I4/m). X-ray absorption spectroscopy confirmed the presence of Co2+/Mo6+ and Ni2+/Mo6+ pairs in the oxygen-stoichiometric compounds. The samples contain a limited concentration of oxygen vacancies in the reducing atmospheres at an anode. Reoxidation is facile below 600 °C; they become antiferromagnetic at low temperatures TN = 37 and 80 K for M = Co and Ni, respectively. As an anode with a 300 μm thick La0.8Sr0.2Ga0.83Mg0.17O2.815 electrolyte and SrFe0.2Co0.8O3−δ as a cathode, Sr2CoMoO6 exhibited maximum power densities of 735 mW/cm2 in H2 and 527 mW/cm2 in wet CH4 at 800 °C; Sr2NiMoO6 shows a notable power output only in dry CH4. The high performance of Sr2CoMoO6 in wet CH4 may be due to its catalytic effect on steam reforming of methane, but some degradation of the structure that occurred in CH4 obscures identification of the ca...

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Double-Perovskite Anode Materials Sr2MMoO6 (M = Co, Ni) for Solid Oxide Fuel Cells

The charge carriers in all of the well-known layered copper oxide high-temperature superconductors1– are holes located in the CuO2planes, the common structural element of these systems. Recently, Tokura et al.5 have reported that doping of Ln2CuO4, where Ln represents Pr, Nd or Sm, with formally tetravalent Ce can produce a high-temperature superconductor with electron carriers. To determine the character of the carrier states in Nd2–xCexCuO4, we have performed X-ray absorption measurements at the Cu K and Ce L3 edges for several different Ce concentrations. We find clear evidence that the electrons introduced by doping fill 3d holes on the Cu atoms, thus converting some Cu2+ ions to Cu+. Hence the nature of the states nearest to the Fermi energy (that is, those responsible for conduction) is qualitatively different from that in the hole-doped superconductors, in which the holes move in a band formed predominantly from O 2p states8–10. As a result, the details of the electron-pairing mechanism could be very different in the two systems11.

Nature of the charge carriers in electron-doped copper oxide superconductors

Systematic Mn K-edge x-ray-absorption spectroscopy (XAS) measurements on samples of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ca}}_{\mathrm{x}}$${\mathrm{MnO}}_{3}$ are reported. Detailed results on the chemical shift and pre-edge feature spectral strength (both indicators of the Mn d-hole count) are discussed. The overall chemical shift across the series is compared to standard materials and is consistent with the identification of the endpoint perovskites with the ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ states. The detailed compositional dependence of the chemical shift and the strength of the pre-edge feature both indicate a uniform Ca-induced increase in the Mn d-hole count for xg0.2 and an anomalous break from this behavior for x values less than x\ensuremath{\approx}0.2. Careful x-ray-diffraction measurements of the lattice parameter variation are also found to manifest changes near x\ensuremath{\approx}0.2 and the chemical shift results are shown to scale with the lattice parameter results. Additional XAS results on air prepared and oxygen annealed samples reveal a variation in the chemical shift response to excess oxygen across this series. These XAS results are discussed in terms of the important Mn d-hole count variation across this system.

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Mark Croft

Papers

Preparation of Y‐Ba‐Cu oxide superconductor thin films using pulsed laser evaporation from high Tc bulk material

Large Low-Field Magnetoresistance in Perovskite-type CaCu 3 Mn 4 O 12 without Double Exchange

Double-Perovskite Anode Materials Sr2MMoO6 (M = Co, Ni) for Solid Oxide Fuel Cells

Nature of the charge carriers in electron-doped copper oxide superconductors

Systematic Mn d-configuration change in the La 1 − x Ca x MnO 3 system: A Mn K-edge XAS study