EDS and TEM Study of the Family of Compounds with a Structure Based on [Bi12O14]∞ Columns in the Bi2O3–MoO3 Binary System (original) (raw)
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Journal of Solid State Chemistry, 2010
Series of compositions Bi 2 (M 0 x M 1 À x) 4 O 9 with x ¼ 0.0, 0.1,y, 1.0 and M 0 /M ¼Ga/Al, Fe/Al and Fe/Ga were synthesized by dissolving appropriate amounts of corresponding metal nitrate hydrates in glycerine, followed by gelation, calcination and final heating at 800 1C for 24 h. The new compositions with M 0 / M¼ Ga/Al form solid-solution series, which are isotypes to the two other series M 0 /M¼ Fe/Al and Fe/Ga. The XRD data analysis yielded in all cases a linear dependence of the lattice parameters related on x. Rietveld structure refinements of the XRD patterns of the new compounds, Bi 2 (Ga x Al 1 À x) 4 O 9 reveal a preferential occupation of Ga in tetrahedral site (4 h). The IR absorption spectra measured between 50 and 4000 cm À 1 of all systems show systematic shifts in peak positions related to the degree of substitution. Samples treated in 18 O 2 atmosphere (16 h at 800 1C, 200 mbar, 95% 18 O 2) for 18 O/ 16 O isotope exchange experiments show a well-separated IR absorption peak related to the M-18 O cM vibration, where O c denotes the common oxygen of two tetrahedral type MO 4 units. The intensity ratio of M-18 O c /M-16 O c IR absorption peaks and the average crystal sizes were used to estimate the tracer diffusion coefficients of polycrystalline Bi 2 Al 4 O 9 (D ¼ 2 Â 10 À 22 m 2 s À 1), Bi 2 Fe 4 O 9 (D ¼ 5 Â 10 À 21 m 2 s À 1), Bi 2 (Ga/Al) 4 O 9 (D ¼2 Â 10 À 21 m 2 s À 1) and Bi 2 Ga 4 O 9 (D ¼2 Â 10 À 20 m 2 s À 1).
Study of the Formation of Bi2Te4O11
Journal of Solid State Chemistry, 1996
For single-crystal growth of bismuth tellurites it is im-The solid state reaction in a 1 : 4 mole ratio mixture of Bi 2 O 3 portant to know the details of the solid state reaction beand TeO 2 and the polymorphic phase transition of Bi 2 Te 4 O 11 tween Bi 2 O 3 and TeO 2. There are some contradictions in have been investigated using differential scanning calorimetry the published phase diagrams of this reaction (12, 13). In (DSC), electron microprobe, X-ray powder diffraction (XPD), spite of the fact that bismuth tellurites can easily be oxiand selected area electron diffraction (SAED) analysis in the dized in air there are still some open questions concerning 25-730؇C temperature range. Upon heating first a 8Bi 2 Te 4 O 11 ؉ the oxidation process (12-14). Bismuth tellurium oxide 23TeO 2 eutectic is formed, which melts at 598.9؇C. In this melt compounds have anion-deficient fluorite structures. It is the excess of Bi 2 O 3 reacts further and the Bi 2 O 3 ؉ 4TeO 2 ؍ not yet clear whether complete oxidation leading to the Bi 2 Te 4 O 11 reaction takes place. The cubic modification is formed filling of all vacant oxygen sites is possible. by fast crystallization of the Bi 2 Te 4 O 11 melt. The structure of The chemical reaction between Bi 2 O 3 and TeO 2 can be the cubic Bi 2 Te 4 O 11 can be characterized by the lattice constant described by the following equation: of a ؍ 5.6397(5) Å and space group Fm3m. The main product of a slow cooling is the same cubic polymorph although a subordinate formation of the monoclinic phase is also observed. (1 Ϫ x)/2Bi 2 O 3 ϩ xTeO 2 ϭ Bi 1Ϫx Te x O (3ϩx)/2. The -Bi 2 Te 4 O 11 cubic phase undergoes a monotropic transformation into the ␣-Bi 2 Te 4 O 11 monoclinic modification at temper-Bi 2 Te 4 O 11 (x ϭ 0.667) is the first compound formed in the atures higher than 400؇C. The cubic Ǟ monoclinic transition solid state reaction of Bi 2 O 3 and TeO 2. The structure of is the result of an ordering in one set of ͕111͖ planes and the Bi 2 Te 4 O 11 was first studied by Frit et al. (17) and the comorthogonality of the cubic phase in the [110] projection changes plete structure analysis was carried out by Rossel et al. to monoclinic symmetry. The melting enthalpies of the cubic (18). These authors described only the monoclinic Ͱ-modi--phase and the monoclinic ␣-phase are 35.9 ؎ 3.3 J/g and fication. Demina et al. (15) reported on X-ray investigation 84.3 ؎ 4.3 J/g respectively.
Materials Research Bulletin, 1997
The structureof BizcMod.b was solved using a combinationof X-ray and neutrondiffraction. The finalrefinementwas completedusinghighresolution neutron powder diffraction in a monocliniccell = 1.17456(3)nm, b = 0.57988(1)nm, c = 2.47919(5)nm,~= 102.903(1)0, P2/c], neglectinga very subtle triclinic distortionresolved only with synchrotrons X-ray data. This phase exhibitsa solid volubilityrange of approximately2.6 S Bi/Mo <2.8, with the idealratio at 2.6 and one of the Bi sitesdisordered.The structureis rationalized by comparisonwith other bismuth molybdatesusing valence bond sums and Madelung site potentials. As with several other bismuth molybdates,there is significantchargetransferbetweenBi-richchannelsand surroundingmolybdenumtetrahedral in this fluorite-relatedstructure. @1 E S
On the Phase Transitions of Bi2Te4O11
Journal of Solid State Chemistry, 1998
The polymorphic phase transitions of Bi 2 Te 4 O 11 have been investigated using X-ray powder diffraction (XPD), selected area electron diffraction (SAED), and differential scanning calorimetry (DSC) in the 25-730°C range. The metastable cubic modification, which forms under fast crystalization of the Bi 2 Te 4 O 11 melt, has fluorite-type structure. Each cation position is filled with bismuth and tellurium in 1/3-2/3 ratio, while the anion positions are occupied by oxygen in 11/12 site occupancy (evenly distributed vacancy), representing a structure with no chemical ordering. The first process in the transition of cubic phase is cation ordering along a cubic [1 1 1] direction. The ordering process has a small activation energy, but the structure reordering itself is exotherm. The final stage of this ordering is the separation of the cations into the triplets of planes forming two types of structural slabs with composition Bi 2 Te 2 O 7 and TeO 2. Every third plane contains only Te, and the first two are occupied by equal amounts, of Bi and Te with random distribution. The oxygen content is lower than what would be expected based on the available anion sites in the ideal fluorite structure, and these positions are populated by oxygen in a statistical (random) distribution. The next step of transition is the ordering of oxygen vacancy. The oxygen vacancy is concentrated at the Bi-containing layers in accordance with the fluorite-based structural model of the Bi 2 Te 2 O 7 layers. The result is monoclinic Bi 2 Te 4 O 11 with P2 1 /n symmetry. There are, however, several grains in the sample that show the coexistence of an exclusively cation-ordered, fluorite-type structure and that of Rossel's model. This indicates an intermediate or alternative stage of the phase transition, in which the Bi 2 Te 2 O 7 and TeO 2 slabs are already formed, but the oxygen coordination in the TeO 2 layer is still fluorite-type hexahedral. The formation of the rutile-type TeO 2 slabs can be a next step of the transition. The boundary between the two observed phases is irregular. The solid state first order phase transformation can be assumed at the grain boundaries.
New Structural and Electrical Data on Bi–Mo Mixed Oxides with a Structure Based on [Bi12O14]∞Columns
Journal of Solid State Chemistry, 1999
We recently described a new family of oxide anion conductors with a structure based on [Bi 12 O 14 ] columns (J. Solid. State Chem. 122, 394 (1996)). The parent compound of this series can be formulated as Bi 26 Mo 10 O 69 and formation of a solid solution, in the Bi 2 O 3-MoO 3 binary system, in the range 2.574 Bi/Mo42.77 was established. The stoichiometry of this series was questioned by R. Enjalbert et al. (J. Solid State Chem. 131, 236 (1997)), but confirmed by D. J. Buttrey et al. (Mater. Res. Bull. 32, 947 (1997)). The first part of this paper is devoted to a refutation criticisms by R. Enjalbert et al. In the second part, a comparison with other Bi 2 O 3-based oxide anion conductors enables us to propose an iono-covalent description of this novel structure type, taking into account all the structural and electrical features, especially new neutron powder diffraction refinement and conductivity measurements under variable oxygen partial pressures.
2012
Bu calismanin amaci; zamanla ozellikleri bozulmayan ve calisma sartlari altinda iyonik iletkenligini koruyan elektrolit/elektrolitler tespit etmektir. Bu dogrultuda, (Bi2O3)1-xy(Ho2O3)x(Dy2O3)y uclu sistemin (x=%11, 12, 13, 14 mol ve y=% 4, 3, 2, 1 mol, katki konsantrasyonu) numuneleri katihal reaksiyonu ile 48 saat 750°C isil isleme tabi tutularak hazirlandi. Kati Oksit Yakit Hucresi (SOFC) icin en iyi kati elektrolit ozelliklere sahip olabilecek numunelerin yapisal ozellikleri X-isinlari difraktometresi (XRD), elektriksel ozellikleri dort-nokta metodu ve termal ozellikleri diferansiyel termal analiz (TG / DTA) olcum sistemleri ile olculdu. XRD olcumleri 48 saat 750°C isil islem sonucunda butun numuneler δ- Bi2O3 fazinda kararli oldugunu gosterdi. The aim of this study is to find an electrolyte which does not have any degradation in its properties with time this maybe caused either interaction between the different electrochemical cell materials or by instability of the ionic condu...