nan Ismunandar

Effect of temperature on cation disorder in ABi2Nb2O9 (A=Sr, Ba)

The influence of thermal annealing on cation disorder in ABi 2 Nb 2 O 9 (A=Sr, Ba) has been studied using synchrotron powder X-ray diffraction methods. BaBi 2 Nb 2 O 9 adopts a tetragonal (I4 1 /mmm) structure, whilst SrBi 2 Nb 2 O 9 is orthorhombic, space group A2 1 am, irrespective of the annealing conditions. In both complexes the A-type cations, Sr and Ba, are disordered over the perovskite and Bi 2 O 2 layers. Quenching the samples from high temperature results in a slight increase in both the cell volume and the degree of disorder, the extent of disorder being greater in the Ba complex. Variable temperature diffraction studies are also reported.

Structural phase transitions in the layered bismuth oxide BaBi4Ti4O15

Abstract The structure of the n =4 Aurivillius oxide BaBi 4 Ti 4 O 15 has been studied at room temperature using powder neutron diffraction, and from 300 to 1000 K using synchrotron X-ray diffraction methods. The structure is orthorhombic (space group A 2 1 am ) at 300 K and transforms to a tetragonal ( I 4/ mmm ) structure near 700 K.

SOFC composite electrolyte based on LSGM-8282 and zirconia or doped zirconia from zircon concentrate

The aim of this research is to study zirconia-based electrolyte materials to increase the commercial value of zircon concentrate as a side product of tin mining industries. Synthesis of CaO-Y2O3-ZrO2 (CYZ) and 8mol% Y2O3-ZrO2 (8YSZ) was carried out by solid state reaction. The result shows that ZrO2 presents in tetragonal phase. Doping of Y2O3 into ZrO2 allows a phase transformation from tetragonal into cubic structure with small percentage of monoclinic phase. Meanwhile, doping of CaO-Y2O3 allows a phase transformation into a single cubic phase. These phase transformations enhance the ionic conductivity of the material. Introduction of 10wt% of LSGM-8282 into CYZ (CYZ-L90:10) allows further improvement of inter-grain contact shown by SEM morphological analysis and leads to the enhancement of ionic conductivity.

Further Insight into the Definite Morphology and Formation Mechanism of Mesoporous Silica KCC-1

The unique three-dimensional pore structure of KCC-1 has attracted significant attention and has proven to be different compared to other conventional mesoporous silica such as the MCM-41 family, SBA-15, or even MSN nanoparticles. In this research, we carefully examine the morphology of KCC-1 to define more appropriate nomenclature. We also propose a formation mechanism of KCC-1 based on our experimental evidence. Herein, the KCC-1 morphology was interpreted mainly on the basis of compiling all observation and information taken from SEM and TEM images. Further analysis on TEM images was carried out. The gray value intensity profile was derived from TEM images in order to determine the specific pattern of this unique morphology that is found to be clearly different from that of other types of porous spherical-like morphologies. On the basis of these results, the KCC-1 morphology would be more appropriately reclassified as bicontinuous concentric lamellar morphology. Some physical characteristics such as the origin of emulsion, electrical conductivity, and the local structure of water molecules in the KCC-1 emulsion were disclosed to reveal the formation mechanism of KCC-1. The origin of the KCC-1 emulsion was characterized by the observation of the Tyndall effect, conductometry to determine the critical micelle concentration, and Raman spectroscopy. In addition, the morphological evolution study during KCC-1 synthesis completes the portrait of the formation of mesoporous silica KCC-1.

Structural and magnetic studies of manganese-containing pyrochlore oxides

Abstract The preparation of a number of manganese-containing pyrochlores of the type Ln 2 (MnSb)O 7 , Ln=Sm–Dy and Y, and Bi 2 (MnM)O 7 , M=Nb, Ta and Sb, at ambient pressure is described. The structures were refined from powder X-ray and/or neutron diffraction data and the Rietveld method. All the oxides of the type Ln 2 (MnSb)O 7 , Ln=Sm–Dy or Y, have a regular pyrochlore structure with the cubic cell parameter being strongly dependent on the ionic radii of the Ln 3+ cation. Bi 2 (MnM)O 7 , M=Nb, Ta or Sb, also adopt a regular pyrochlore structure and their magnetic properties indicate that Mn 2+ is present in these oxides.

Ionic conductivity of Bi2NixV1−xO5.5−3x/2 (0.1 ≤ x ≤ 0.2) oxides prepared by a low temperature sol-gel route

Solid oxides fuel cells (SOFCs) is one technology that could contribute toward future sustainable energy. One of the most important components of an SOFC is the electrolyte, which must have high ionic conductivity. Cation substitution of vanadium in Bi4V2O11 yields a family of fast oxide ion conducting solids known collectively as the BIMEVOXes (bismuth metal vanadium oxide), which have the potential to be applied as electrolytes in SOFCs. The purpose of this work is to study the effect of Ni concentration, when used as a dopant, on the ionic conductivity of Bi2NixV1−xO5.5−3x/2 (BINIVOX) oxides (0.1 ≤ x ≤ 0.2) when prepared by a sol gel method. The gels were calcined at 600 °C for 24 h to produce pure BINIVOX. These oxides were found to exhibit the γ-phase structure with tetragonal symmetry in space group I4/mmm. Ionic conductivity of BINIVOX at 300 °C were 6.9 × 10−3 S cm−1, 1.2 × 10−3 S cm−1, and 8.2 × 10−4 S cm−1, for x = 0.1; 0.15; and 0.2; respectively; and at 600 °C were 1.1 × 10−1 S cm−1, 5.3 × 10−...

Synthesis of 8YSZ‐LSGM Composite Thick Film Ceramics for Solid Electrolyte From Nanopowder Utilizing Local Zircon Prepared Using Sol Gel Process

Thick film ceramics of 8% mol Y2O3 doped‐ZrO2 (8YSZ)‐La0.8Sr0.2Ga0.2Mg0.8O3 (LSGM) composite for solid electrolyte have been synthesized from nanopowder. Concentration of LSGM was 0 and 10% weight. A paste for the thick films was made from 8YSZ nanopowder prepared using sol gel method and LSGM powder prepared by solid state reaction. Precursors for the 8YSZ nanopowder preparation were ZrOCl2⋅8H2O derived from local zircon as byproduct of Tin processing at Bangka Island using caustic fussion method, and Y(NO3)3. The thick films were produced by screen printing technique on alumina substrates. The films were sintered at 1500° C for 2 hours in air. X‐ray diffraction (XRD) data showed that the nanopowder of 8YSZ was well produced with broad peaks. The particle size of the 8YSZ powder was about 12 nm as calculated using Debye Scherrer method. The thick films of 8YSZ and 8YSZ‐LSGM (90:10 in weight %) composite could be produced, however, the films still contain voids. The ionic conductance of the YSZ‐10LSGM fil...

Structural Studies of Five Layer Aurivillius Oxides: A 2 Bi 4 Ti 5 O 18 (A ¼ Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A 2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi2O2]2+ layers interleaved with perovskite-like [A 2Bi2Ti5O16]2− blocks. The oxides were found to be orthorhombic (space group B2cb) as a consequence of tilting of the TiO6 octahedra coupled with cation displacement. The tilting is a consequence of the mismatch between the Bi2O2 and perovskite-like layers.

Raman scattering study of the effect of A- and B-site substitution on the room-temperature structure of ABi4Ti4O15

Aurivillius-type materials exhibit promising ferroelectric and multiferroic properties that can be tailored via chemistry variations in the perovskite block. Hence, it is important to clarify the relations composition-structure, also on a local-scale level. The aim of this contribution is to give further insights into the effect of A- and B-site cations to the room-temperature local structure of Aurivillius four-layered ABi4Ti4O15 (A = Sr, Pb, Ba) and Pb1−x Bi4+x Ti4−x Mn x O15 (x = 0, 0.2, 0.4) by Raman scattering. The effect of A-site cation to the local structure of perovskite block was identified by the phonon mode near 750 and 870 cm−1 arising from BO6 stretching. A-site Ba2+, having the largest ionic radius among the considered elements, significantly stiffens the TiO6 octahedra, as derived from the fact that the TiO6 stretching modes have the highest wavenumber for BaBi4Ti4O15, i.e. the Ti-O bond strength is strongest for this compound. The replacement of Ti4+ by Mn3+ cation at the B- site also influences the B-O bond. The comparison of the phonon modes near 700 and 870 cm−1 in Pb1−x Bi4+x Ti4−x Mn x O15 with x = 0, 0.2, and 0.4 shows that the lowest wavenumber, which is due to the elongation of Ti-O bonds is observed for x = 0.4.

Metal (Fe, Co, Ni) supported on different aluminas as Fischer-Tropsch catalyst

This research aimed to compare the physico-chemical properties of the same metal M (M = iron, cobalt, nickel) supported on aluminas with different morphology and pore size as Fischer-Tropsch catalyst. The aluminas applied as support were alumina synthesized through hydrothermal process, alumina formed by pretreatment of catapal and commercial alumina which named as Ahy, Aca, and Aco respectively. Ahy has uniform morphology of nanotubes while Aca and Aco showed non-uniform morphology of particle lumps. The particle lumps of Aca were larger than those of Aco. Ahy, Aca, and Aco respectively has average pore diameter of 2.75, 2.86 and 2.9 nm. Metals were deposited on the supports by incipient-wetness impregnation method. The catalysts were characterized by XRD, H2-TPR, and H2 chemisorption. Catalyst acitivity test for Fischer-Tropsch reaction was carried out in a micro reactor at 200 °C and 1 atm, and molar ratio of H2/CO = 2:1. The metal oxide particle size increased in the order M/Aco < M/Aca < M/Ahy. The c...