19 research outputs found
ChemInform Abstract: Charge Disproportionation and Magnetoresistivity in a Double Perovskite with Alternate Fe 4+
Crystallographic Characterization of (Sr\u3csub\u3e2-x\u3c/sub\u3eCa\u3csub\u3ex\u3c/sub\u3e)(MgTe)O\u3csub\u3e6\u3c/sub\u3e Double Perovskite via Electron Diffraction
Complex perovskite oxides [(A,Aâ)(B,Bâ)O3] are ubiquitous in electronic applications. An understanding of such structures and the mechanisms which affect them is essential in predicting and controlling the material properties. Structural distortions away from the ideal cubic aristotype may include tilting or deformation of the oxygen octahedra, chemical ordering or displacement of cations, or defect-induced lattice strain. Each of these mechanisms can alter the symmetry of the perovskite, resulting in a doubled supercell, with a corresponding effect on properties. By investigating the appearance of superlattice reflections in electron diffraction patterns, a summary of the octahedral tilting (tilt system) of the structure can be identified, cation ordering inferred, and space group symmetry established. In the case of the (Sr2-xCax)(MgTe)O6 system, a phase transformation occurs from a tetragonal I4/m symmetry at x = 0 (Sr2MgTeO6) to monoclinic P21/n symmetry for x â„ 0.5; however, B-site cation ordering causes Âœ{odd,odd,odd} type reflections in all compositions, complicating the crystallographic characterization
Structure of Compounds in the Sr1â3x/2CexTiO3 Homologous Series
Four compositions in the Sr1â3x/2CexTiO3 homologous series, corresponding to x = 0.1333, 0.1667, 0.25, and 0.4, have been produced by conventional solid-state processing. The structure of these compounds was analyzed by X-ray, electron, and neutron diffraction. While no superlattice can be observed via X-ray diffraction, both electron and neutron diffraction show evidence of a noncubic supercell caused by antiphase tilting of oxygen octahedra. The most likely space group is R3Ì
c, corresponding to an aâaâaâ tilt system, except for the composition x = 0.4, for which an even more complex superstructure is observed. The degree of tilt increases with increasing x
Room-Temperature Ferromagnetic Sr3YCo4O10+ÎŽ and Carbon Black-Reinforced Polyvinylidenefluoride Composites toward High-Performance Electromagnetic Interference Shielding
Effective Size of Vacancies in the Sr\u3csub\u3e1- 3\u3cem\u3ex\u3c/em\u3e/2\u3c/sub\u3eCe\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3e/TiO\u3csub\u3e3\u3c/sub\u3e Superstructure
Vibrational spectroscopic study of Sr2ZnTeO6 double perovskites.
Sr2ZnTeO6 ceramics were prepared by the solid-state route and their vibrational phonon modeswere investigated using optical
spectroscopic techniques, for the first time. X-ray diffraction (XRD) and Raman and infrared spectroscopies were employed to
investigate the structures of these perovskite materials and the results analysed together with group-theoretical predictions.
The number and behaviour of the first-order modes observed in both spectroscopic techniques are in agreement with the
calculations for a tetragonal I4/mspace group. The complete set of the optical phononmodeswas determined, and the intrinsic
dielectric properties of the materials were evaluated, allowing us to discuss their potential application in microwave (MW)
circuitry
Crystal Structure of Sr\u3csub\u3e0.4\u3c/sub\u3eCe\u3csub\u3e0.4\u3c/sub\u3eTiO\u3csub\u3e3\u3c/sub\u3e Ceramics
A cerium-doped SrTiO3 compound with the composition Sr0.4Ce0.4TiO3 has been produced by conventional solid-state processing. The structure of this compound was analyzed by X-ray, electron, and neutron diffraction. While no superlattice can be observed via X-ray diffraction, both electron and neutron diffraction show evidence of a noncubic supercell caused by antiphase tilting of oxygen octahedra. The most likely space group is C2/c, corresponding to an a-b-b- tilt system. Octahedra are tilted by ~5° about the pseudo-cubic a-axis and ~1.5° about the pseudo-cubic b- and c-axes
Structural Characterization of BâSite Ordered Ba<sub>2</sub>Ln<sub>2/3</sub>TeO<sub>6</sub> (Ln = La, Pr, Nd, Sm, and Eu) Double Perovskites and Probing Its Luminescence as Eu<sup>3+</sup> Phosphor Hosts
Ba<sub>2</sub>Ln<sub>2/3</sub>TeO<sub>6</sub> (Ln = La, Pr, Nd, Sm, and
Eu) double perovskites were synthesized via solid-state ceramic route.
Preliminary X-ray diffraction studies indicated a pseudocubic structure
with lattice parameters ranging from 8.55 to 8.44 Ă
for the substitution
of rare earths from La to Eu. Raman spectra show the frequency dependence
of various Raman bands with respect to rare-earth substitution and
exhibit a significant shift in peaks to higher wavenumber region,
which was observed only for symmetric stretching modes of LnO<sub>6</sub> and TeO<sub>6</sub> octahedra. In accordance with observed
number of bands and group theoretical predictions, the most likely
symmetry of all compounds in the Ba<sub>2</sub>Ln<sub>2/3</sub>TeO<sub>6</sub> system was found to be monoclinic with <i>P</i>2<sub>1</sub><i>/n</i> space group. Rietveld refinement
of the XRD patterns further confirmed the <i>P</i>2<sub>1</sub><i>/n</i> space group and also the 1:1 rock salt
ordering of the B-site cations. Diffuse reflectance spectra of Ba<sub>2</sub>Ln<sub>2/3</sub>TeO<sub>6</sub> showed the optical bandgaps
of these compounds between 3.9 and 4.8 eV, indicating the suitability
as luminescent host material. The reduction in bandgap energy with
lanthanide contraction of rare-earth ions is attributed to the widening
of conduction band with octahedral tilting. Photoluminescence (PL)
spectra and PL excitation spectra of Ba<sub>2</sub>La<sub>2/3â<i>x</i></sub>Eu<sub><i>x</i></sub>TeO<sub>6</sub> (<i>x</i> = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15) were investigated
and found to exhibit bright orange-red emission under UV excitation.
Chromaticity coordinates closely resemble those of commercial red
phosphor Sr<sub>2</sub>Si<sub>5</sub>N<sub>8</sub>:Eu<sup>2+</sup>, which points toward the possible applicability of these new red
phosphors in solid-state lighting industry. Finally, JuddâOfelt
intensity parameters Ω<sub>λ</sub> (λ = 2 and 4)
were calculated, which indicate that Eu<sup>3+</sup> ions occupy the
symmetric octahedral B-site of the Ba<sub>2</sub>La<sub>2/3</sub>TeO<sub>6</sub>