Pseudo-cubic structure

Fig. 9.03. (a) Clinographic projection of the unit cell of the tetragonal (pseudo-cubic) structure of die low-temperature fi form of Ag2HgI4. (b) Clinographic projection of the unit cell of the cubic structure of the high-temperature a form. 

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. 

Lee, U.-H., Lee, H Wen, S., Mho, S., and Kwon, Y.-U. (2006) Mesoporous titania thin films with pseudo-cubic structure synthetic studies and applications to nanomembranes and nanotemplates. Microporous Mesoporous Mater, 88 (1-3), 48-55. 

A kinetic resolution of racemic sulphoxides was observed in the reduction by chiral polyiminoalanes. The efficiency of this process depends on the molecular structure of the polyiminoalane. With open pseudo-cubic tetra [JV-(l-phenylethyl)]imidoalane, unreacted sulphoxides were isolated in enantiomeric enrichment up to 75%. Optical purity was shown to increase with increasing the reaction temperature, a maximum enrichment being observed between 55 and 70 °C336. 

On beginning the investigation of the tetragonal pseudo-cubic mineral braunite, 3Mn303.MnSi03, we found the unit of structure to be closely related to that of bixbyite, and, indeed, to have dimensions nearly the same as those for two superimposed bixbyite cubes. This led us to... 

Nevertheless it may be observed that, in some specific cases, reference to a pseudo-face-centred tetragonal cell may be useful, for instance to compare the structure under examination with a face-centred cubic structure. 

The tI10-MoNi4 type is another superstructure based on face-centred cubic pseudo-cells. In the projection shown in Fig. 3.36, inside the true cell, the pseudo-cubic subcell (aps = 362 pm, cps = 356.4 pm) has been evidenced by dotted lines. Close-packed layers can be identified in this structure they are stacked in a 15 close-packed repeat sequence. 

Figure 6.12 Calculated diffraction patterns for Pb(Zro.52Tio.48)03 thin films with a. ..c/a/c/a... domain-structured tetragonal phase and a pseudo-cubic phase. The lattice parameters for the two phases were measured by XRD-RSMs.

The detailed structures of zeolites are varied and complex, but the common pseudo-cubic basket-like frameworks of linked tetrahedra are depicted in Figure 1.7. These typify the unit cage structures found for the mineral faujasite and the synthetic zeolites whose structures are generically described as types A, X, and Y. The constitution, channel diameters, and ion exchange capacities for various natural and synthetic zeolites are shown in Table 1.4. 

When the pseudo-spherical ammonium ion is mostly replaced by a truly spherical ion the complex sequence of phase changes found in the pure ammonium halides is suppressed. The mixed potassium ammonium halide salts retain their NaCl cubic structure down to the lowest temperatures. The alkali metal ions support the structure leaving the ammonium ions as free to rotate at 1 K as at 300K [13]. The INS spectrum of this system is quite different from the pure salt and there are no sharp features in any region of the spectrum. We shall analyse the impact that this freedom has on the internal modes about 1400 cm. ... 

Cag.sNaAlgOis possesses an orthorhombic unit cell, space group Pbca. The mean A1—O bond length is 1.751(1) A, and the A1 atoms are distributed at positions very near the corners of pseudo-cubic sub-cells. The crystal structures of a number of nickel aluminosilicates have been determined. " ... 

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