Characterization, pyrochlore

The compounds characterized by X Me = 3.5 have a common formula of M2Me205F2 and crystallize either in a pyrochlore [192] or a veberite [229] type structure. According to X-ray powder diffraction patterns, the structure of Na2Nb205F2 can be regarded as a super-structure of pyrochlore, which is made up of octahedrons connected in layers and arranged in the (111) direction. The layers are linked via octahedrons so that each octahedron in one layer shares three vertexes with an octahedron in the adjacent layer. 

Because Nip4 (under aHF) loses 1/2 F2 above -60°C it remains poorly characterized but the trifluoride has been prepared in three forms approximately hexagonal-close-packed rhombohedral (Ji-NiFj), hexagonal tungsten bronze (//-NiFs) and pyrochlore (P-NiFs) the last two having small content (and corresponding Ni(II) incorporation). The NiFs forms can be kept indefinitely at 20°C in a dry atmosphere but all lose fluorine slowly in aHF at ambient temperature. 

While metal oxides and mixed metal oxides have often been considered for various electrocatalytic applications, they are often limited by low electronic conductivity and/or low surface area. One series of mixed metal oxides with the pyrochlore structure has been discovered ( ) that has demonstrated high catalytic activity for electroreduction and electroevolution of oxygen 2) and the selective electrooxidation of certain organics 3). These materials, which are characterized by high electronic conductivity and can be prepared in high surface area form, are described by the general formula ... 

General Chemical and Physical Characterization. The x-ray diffraction data, chemical analyses by x-ray fluorescence and the effects of various synthesis parameters explored in this study lead to the conclusion that a new series of pyrochlores represented by formula 1 has been synthesized. The substitution of the larger post transition element cation for the noble metal cation on the octahedrally coordinated B-site leads to a considerable enlargement of the pyrochlore s cubic unit cell dimension. The relationship between lattice parameter (ag) and extent of substitution of ruthenium by either lead or bismuth is linear as shown in Figure 1. 

Methods for the preparation of the selenate Bi2(Se04)3 have been investigated and the compound has been characterized. Powder X-ray data have been collected for the pyrochlore Bi2Ru207, Bi2U06, and 811982703. ... 

Pakhare D, Wu H, Narendra S, Abdelsayed V, Haynes D, Shekhawat D, Berry D, Spivey J (2013) Characterization and activity study of the Rh-substituted pyrochlores for C02(dry) reforming of CH4. Appl Petrochem Res 3(3-4) 117-129... 

The problem of the frustrated Ising antiferromagnet on a (pyrochlore) lattice of comer-shared tetrahedra has been related to the water ice problem [14]. Spin ice materials are characterized by disorder of magnetic ions even when said ions are at very low temperatures. AC magnetic susceptibility measurements find evidence for a dynamical freezing of the magnetic moments as the temperature is lowered somewhat below the temperature at which the specific heat displays a maximum. 

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