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Polycrystalline samples of La0.67Li0.2Ti0.8Al0.2 with different crystal microstructures have similar general dielectric behavior. The materials show very high dielectric permittivity ([variant_greek_epsilon]′≈300 000) over relatively wide frequency and temperature ranges with no apparent dependence on the microstructure. The impedance spectroscopy study indicates that the origin of the high dielectric constant is a barrier layer capacitor effect due to depletion of Li ions at the grain boundaries of these Li-conducting materials. However, influence of the three dimensional microstructure domains on bulk properties such as electrical resistance and capacitance is observed. [ABSTRACT FROM AUTHOR]

The ordered double perovskite Pb2NiReO6 has been prepared at 6 GPa and temperatures ranging from 1273 to 1373 K. Its crystal structure determined by X-ray powder diffraction and selected area electron diffraction shows monoclinic symmetry with centrosymmetric space group I2/m (a = 5.6021(1) Å, b = 5.6235(1) Å, c = 7.9286(1) Å and β = 90.284°(1)). High angle annular dark field microscopy studies reveal the existence of compositional microdomains. The compound displays a re-entrant spin-glass transition from a ferrimagnetic ordering below TN ∼ 37 K between the Re+5 and Ni+3 (high spin configuration) magnetic sublattices to a spin-glass configuration. Magnetic field dependent magnetization measurements revealed wasp-waisted hysteresis loops at 5 K. These shaped features originate from the antiferromagnetic/ferromagnetic (AFM/FM) competing interactions. [ABSTRACT FROM AUTHOR]

Structural properties and the influence of d electrons' insertion in PbTiO3 have been determined in the study of PbM1-xMx′O3 (M, M′ = Ti, Cr, and V) solid solutions by means of X-ray diffraction, high-resolution transmission electron microscopy, magnetization measurements, and strain mapping analysis. PbTi1-xVxO3 is the only system that preserves the same space group (P4mm) for all x, whereas PbTi1-xCrxO3 and PbV1-xCrxO3 change to cubic (Pm3m) at x = 0.30 and 0.4, respectively. These values have been related with the percolation threshold for a cubic net (Pc = 0.31). The microscopy study coincides with the X-ray diffraction determination, and neither supercell nor short-range order maxima are observed. However, for x ≥ 0.7 in PbTi1-xCrxO3 the presence of modulated zones is observed in both the electron diffraction pattern as well as high-resolution transmission electron micrographs, as is typical for PbCrO3.1 Furthermore, the tetragonal region in PbV1-xCrxO3 suffers a great stress because of the contrast of [Cr-O6] octahedra and [V-O5] square-based pyramids end members basic units. [ABSTRACT FROM AUTHOR]

We show that an appropriate analysis of the electron energy loss spectra in relation to the Cr–C bonds gives a reliable methodology to obtain the oxidation state in chromium oxides. It is based on the energy difference between the Cr L3 and OK edges, which acts as a measure of the binding energy difference between the Cr 2p3/2 and O 1s core levels. [ABSTRACT FROM AUTHOR]

High dielectric permittivity ([variant_greek_epsilon]′∼500 000) has been observed in polycrystalline samples of La0.67Li0.25Ti0.75Al0.25O3 over a large frequency range (∼103 Hz) and different temperatures. Complex impedance spectroscopy measurements demonstrate that the origin of the high dielectric constant can be attributed to a barrier layer capacitor associated with grain boundary effects in the ion conducting material. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of La0.67Li0.2Ti0.8Al0.2 with different crystal microstructures have similar general dielectric behavior. The materials show very high dielectric permittivity ([variant_greek_epsilon]′≈300 000) over relatively wide frequency and temperature ranges with no apparent dependence on the microstructure. The impedance spectroscopy study indicates that the origin of the high dielectric constant is a barrier layer capacitor effect due to depletion of Li ions at the grain boundaries of these Li-conducting materials. However, influence of the three dimensional microstructure domains on bulk properties such as electrical resistance and capacitance is observed. [ABSTRACT FROM AUTHOR]

The perovskite "PbCrO3" was synthesized at high pressure and high temperature. Its magnetic properties have been investigated by means of magnetization, specific heat, and resistivity measurements. Earlier workers, had concluded it to have a G-type antiferromagnetic structure. However, our measurements suggest a rather more complex situation: first, a weak ferromagnetic transition of the Cr(IV) spins occurs at 245 K; this is followed by a temperature-driven spin reorientation starting at 185 K and ending at 62 K. Since zero-magnetic-field spin reorientation in the "PbCrO3" perovskite should not be expected, an intrinsic "magnetoelectric effect", associated with the lone-pair Pb electrons, seems to be responsible for the observed smooth rotation of the Cr-spins. [ABSTRACT FROM AUTHOR]

The ordered double perovskite Pb2NiReO6 has been prepared at 6 GPa and temperatures ranging from 1273 to 1373 K. Its crystal structure determined by X-ray powder diffraction and selected area electron diffraction shows monoclinic symmetry with centrosymmetric space group I2/m (a = 5.6021(1) Å, b = 5.6235(1) Å, c = 7.9286(1) Å and β = 90.284°(1)). High angle annular dark field microscopy studies reveal the existence of compositional microdomains. The compound displays a re-entrant spin-glass transition from a ferrimagnetic ordering below TN ∼ 37 K between the Re+5 and Ni+3 (high spin configuration) magnetic sublattices to a spin-glass configuration. Magnetic field dependent magnetization measurements revealed wasp-waisted hysteresis loops at 5 K. These shaped features originate from the antiferromagnetic/ferromagnetic (AFM/FM) competing interactions. [ABSTRACT FROM AUTHOR]

The CdCr2O4 spinel transforms to a 10.6% denser new polymorph of the CaFe2O4-type structure at 10 GPa and 1100 °C. This new polymorph has a honeycomb-like structure because of double rutile-type chains formed by [Cr-O6] edge-shared octehedra. This crystal structure is prone to be magnetically frustrated and presents low-dimensional antiferromagnetism at 25 K < T < 150 K, accompanied by more complex interactions as the temperature decreases. These transitions are evidenced by magnetic susceptibility and heat capacity measurements. We also discuss a possible structural mechanism for the transformation. [ABSTRACT FROM AUTHOR]

High dielectric permittivity ([variant_greek_epsilon]′∼500 000) has been observed in polycrystalline samples of La0.67Li0.25Ti0.75Al0.25O3 over a large frequency range (∼10