A2B′B″O6 perovskites: A review

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Recent development in lead-free perovskite piezoelectric bulk materials

Although both A- and B-site cations have the same simple cubic topology in the perovskite structure they typically adopt different patterns of chemical order. As a general rule B-site cations order more readily than A-site cations. When cation ordering does occur, rock salt ordering of B/B′ cations is favored in A2BB′X6 perovskites, whereas layered ordering of A/A′ cations is favored in AA′B2X6 and AA′BB′X6 perovskites. The unexpected tendency for A-site cations to order into layers stems from the bond strains that would result at the anion site if A and A′ cations of different size were to order with a rock salt arrangement. The bonding instabilities that are created by layered ordering are generally offset either by anion vacancies or second order Jahn–Teller distortions of a B-site cation. Novel types of A-site cation ordering can be stabilized by a+a+a+ or a+a+c− tilting of the octahedra.

Cation ordering in perovskites

Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol−gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM) and optical microscopy, UV/vis transmission and absorption spectra, photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 400 °C and the crystallinity increased with the increase of annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of grains with an average size of 90 nm. Patterned gel and crystalline phosphor film bands with different widths (5−60 μm) were obtained. Significant shrinkage and a few defects were observed in the patterned films during the heat treatment process. The doped rare earth ions (A) show...

Fabrication, Patterning, and Optical Properties of Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) Phosphor Films via Sol−Gel Soft Lithography

Influence of cation order-disorder phenomena on the crystal structure, magnetic, and electrical transport properties of new CMR perovskites for LBaMn 2 O 6 - γ (L=Pr, Nd, Sm, Eu, Gd, Tb) series has been investigated. For each rare-earth ion three compounds have been synthesized by the topotactic reduction-oxidation method. Structural investigations have shown the oxygen-stoichiometry LBaMn 2 O 6 compound obtained in air to be cubic with disordered L 3 + and Ba 2 + cations whereas the oxygen-deficient LBaMn 2 O 5 is tetragonal with ordered L 3 + and Ba 2 + and alternate stacking of rare earth and barium containing layers along c. This crystal structure is similar to the YBaCuFeO 5 related one. Another form of oxygen-stoichiometry LBaMn 2 O 6 compound obtained by reoxidation of oxygen-deficient LBaMn 2 O 5 is also tetragonal and retains the ordering of L 3 + and Ba 2 + cations. It is notable that the reoxidized EuBaMn 2 O 6 compound has an orthorhombic unit cell. It is observed that this type of cation ordering leads to considerable increase of transition temperature to paramagnetic state. For example, disordered EuBaMn 2 O 6 compound has magnetic properties similar to spin glass and shows freezing temperature of magnetic moments T f 40 K while ordered EuBaMn 2 O 6 is an inhomogeneous ferromagnet with Curie point T C 260 K. Electrical resistivity behavior correlates with magnetization. Below the T C the Pr, Nd, Sm based compounds undergo a transition to metallic state and demonstrate a peak of magnetoresistance. It is supposed that the remarkable changing of the magnetic and electrical properties of the reoxidized compounds is a consequence of the L/Ba ordering and can be explained on the base of the Goodenough-Kanamori rules for 180° indirect superexchange interactions taking into account an ion size effect in A sublattice of perovskite.

Magnetic and electrical properties ofLBaMn2O6−γ(L=Pr,Nd, Sm, Eu, Gd, Tb) manganites

Metal-semiconductor-transition and spin-glass properties of La(2−x)/3Ba(1+x)/3Mn1−xCuxO3

Oxygen vacancy associate defects were studied by electron paramagnetic resonance (EPR) for the perovskite oxide CaCu 3 Ti 4 O 12 (CCTO), which have a colossal dielectric constant. It is found that the EPR line width of the Cu 2+ –host signal of CCTO correlates with its permittivity. A new signal was found in the second differential of the Cu 2+ –host signal, which we think is associated with a specific copper–oxygen vacancy defect. This signal shows a negative g factor shift with temperature, suggesting a contribution to the conduction. Assuming solid state reactions between the various defects and using the mass action law, we offer a more specific relation between permittivity, the content of oxygen vacancy and the new signal, which might be useful for an indirect but fast oxygen vacancy content determination.

Oxygen vacancy related defect dipoles in CaCu3Ti4O12: Detected by electron paramagnetic resonance spectroscopy

Room-temperature large magnetocaloric effect and critical behavior in La0.6Dy0.1Sr0.3MnO3

Mn 2+ -doped Zn 2 SiO 4 phosphor films were deposited on silicon and quartz glass substrates by sol–gel method (dip-coating). The variations of sol viscosity with time, film thickness with the number of layers were investigated in the Zn 2 SiO 4 :Mn system. The results of XRD and IR showed that the Zn 2 SiO 4 :Mn films remained amorphous below 700°C and crystallized completely around 1000°C. From AFM studies, it was observed that the grains of 0.5–0.8 μm in size packed closely in Zn 2 SiO 4 :Mn films, which were uniform and crack free. The luminescence properties of Zn 2 SiO 4 :Mn films were characterized by absorption, excitation and emission spectra, as well as luminescence decay.

Sol–gel synthesis and characterization of Zn2SiO4:Mn phosphor films

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