Perovskite pseudo-cubic

Cubic (or pseudo-cubic) tungsten bronze type (intermediate between Re03 and perovskite)... 

Fig. 8 Orbital ordering in pseudo-cubic perovskite KCUF3 with vertex-sharing octahedrons [CuFe]. Type a is layer-antiferrodistortive and Type d is layer-ferrodistortive pattern. (After Kugel and Khomskii [19], Reinen and Friebel [16], and Binggeli and Altarelli [20])...

Phase relations in the pseudo-binary systems NdAlOa RAIO3 (R = Eu, Dy, and Er) at RT have been examined by Brusset et al. (1975). According to their study, two kinds of Ndi xEuj A103 solid solutions with rhombohedral and pseudo-monoclinic structure exist in the NdAlOs—EuAlOs system at x < 0.18 and x > 0.25, respectively. It was also claimed that a solid solution with pseudo-cubic symmetry exists in the Ndi j-Erj A103 system when 0.07 phase region between two perovskite-type phases with rhombohedral and orthorhombic structures. In the NdAlOs—DyAlOs system, the boimdary between rhombohedral and pseudo-cubic phases is located near 0.08 molar fractions of DyAlOs-... 

Ultrafme pure BaTi03 powders were obtained by a modified oxalate precipitation method as described previously [13], The powders had a specific surface area of 57 m g and the particle size was nearly spherical from 20 to 30 nm. The main impurities contained in the powders were at the following levels 0.04 wt% Sr, 0.02 wt% Na, and 0.006 wt% K. The Ba/Ti atomic ratio was 1 0.003 for all the powders. The X-ray diffraction (XRD) patterns of nanocrystalline powders apparently correspond to a pseudo-cubic structure without peak splitting of lines such as (002) and (200). We also used Raman spectra to detect local symmetry of the nanocrystalline powder samples. It showed that the local symmetry in the nanopowder appears to be a cubic structure even at a very low temperature of 123 K. Therefore, XRD patterns and Raman spectra revealed that the BaTiOs powder exhibited the commonly reported pseudocubic perovskite structure. 

Phosphors are composed of a semiconductor host and an activator, and both the host and the activator absorb and transfer excitation energy to the excited state of the activator. Double-perovskite A2B(MoAV)Oe with a monoclinic or pseudo-cubic structure, are substantially absorbed in the NUV region [22]. The excitation spectra of the double-perovskite SraCaWOgiEu exhibit a broad absorption band to blue light in the NUV region. This phenomenon occurs because of the charge-transfer (CT) transitions of O to W in the WOg octahedral and the/-/electronic transitions of the Eu activators. 

Over the range of pressure and temperature so far explored in the laboratory, the observed structure of (Mg,Fe)Si03 perovskite is orthorhombic Pbnm (Horiuchi et al. 1987). However, because experiments have not yet accessed the entire pressure-temperature range spanned by the lower mantle, there has for some time been speculation that the structure of this phase at lower mantle conditions may differ from that experimentally observed. The perovskite structure is remarkably rich and accommodates a large variety of polymorphs, which are related by rotations of the SiOe octahedra about the three pseudo-cubic axes (Glazer 1972 Glazer 1975) (Fig. 6). Thus Pbnm may be... 

Rietveld analysis of the neutron powder diffraetion patterns of Lao,64(Tio,92Nbo.o8)02.99 at 769 K, 1281 K, and 1631 K was performed assuming a tetragonal P4/mww strueture a = b k, a, c k. 2op. subseript p denotes pseudo-cubic perovskite-type structure). The refined unit-cell and structural parameters and R factors are summarized in Table 6.2 [11]. The unit-cell parameters increase with temperature, as does the unit-cell volume due to thermal expansion. Figure 6.7(a) shows the crystal structure of the material... 

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