Neue Nb2O5-Modifikationen

Schäfer, Harald; Schulte, Friedrich; Gruehn, R.

doi:10.1002/ange.19640761211

Cited by 31 publications

(23 citation statements)

References 2 publications

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“…Shortly thereafter, Goldschmidt (1958) conducted in situ high-temperature x-ray studies of Nb 2 O s for the first time. He supported the conclusions of Schäfer et al (1954), and the present authors (Holtzberg et al, 1957) that β and a are probably the same, and the conclusions of the present authors that a was the only stable polymorph. Goldschmidt employed a reversed nomenclature to that used by us, calling the high-temperature phase β, and the low-temperature phase a.…”

Section: B Nb 2 0 5 Polymorphismsupporting

confidence: 90%

“…Schäfer and Breil (1952) repeated Brauer's work and corroborated it with the important difference that they claimed to have observed reversibility of the Τ -» M transformation. In a later article, however, Schäfer et al (1954) questioned whether the M and H phases were indeed different. They did not re-examine the reversibility of the T-» M transformation.…”

Section: B Nb 2 0 5 Polymorphismmentioning

confidence: 99%

See 1 more Smart Citation

Nb2O5 and Ta2O5 Structure and Physical Properties

Reisman¹,

Holtzberg²

1970

Refractory Materials

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Section: B Nb 2 0 5 Polymorphismsupporting

confidence: 90%

Section: B Nb 2 0 5 Polymorphismmentioning

confidence: 99%

Nb2O5 and Ta2O5 Structure and Physical Properties

Reisman¹,

Holtzberg²

1970

Refractory Materials

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“…Based on data from the literature (SCHAFER et al 1964 and1966 The fact that during the chemical transport of a V,O,/Nb,O, sample in the molar ratio of 8:92 a phase with the composition Vl,osNb8,94025 was obtained as the transport product and that no Nb,O, was detectable besides that (SCHADOW, OPPERMANN et al) surely can be put down to the fact that in this case the low quantities of Nb,O, transported first were bonded by the quartz of the ampoule walls at the applied high transport temperatures, so that they can escaped detection. There points to it, too, that even the crystals precipitated from the gaseous phase at 873 K had firmly grown on the ampoule walls.…”

Section: Performing Of Experiments and Resultsmentioning

confidence: 99%

Investigations on the Quasi‐binary Subsystem VNb₉O₂₅Nb₂O₅

Schadow¹,

Oppermann²,

Grossmann³

1992

Cryst. Res. Technol.

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By X-ray phase analysis in connection with chemical transport reactions it was proved that two boundary phases coexist in the pseudo-binary subsystem VNb,O,, -Nb,O,. The maximum solubility of V,O, in solid N b , 0 5 which was spectrometrically determined in corresponding chemically transported samples of the system is 0.37% (n/n). The examination of the pseudo-binary system V,O, -Nb,O, (SCHADOW, OPPERMANN et al.) did not allow any safe statements concerning the phases occurring in the subsystem VNb,O,,-Nb,O, and their solubility limits, since there was not achieved an exact phase separation in this range of composition by chemical transport reactions under the conditions applied at that time. Therefore, a detailed investigation was carried out in the subregion VNb,O,, -Nb,O, of the system V,O, -Nb,O,, previously produced VNb,O,, having been used as starting material. Moreover, the temperatures during the chemical transport were lowered considerably in order to achieve a better phase separation. These additional investigations were necessary also because WARINC and ROTH had referred to a phase containing 6 . . . 7 % (n/n) V,O, which is not characterized in more detail in this system. ExperimentalThe VNb,O,, used as starting material for the investigation of the system was produced by annealing a mixture of V,O, and Nb,O, in the corresponding molar ratio. First, the wellhomogenized mixture was pre-annealed in a closed quartz ampoule for 250 h at 873 K, then it was homogenized and subsequently annealed for another 300 h at 1273 K. The following X-ray examination showed that the product of reaction was phase-pure VNb9025. The phase separation in the subsystem VNb,O,,-Nb,O, was carried out with the aid of chemical transport reactions in such a way as described in detail for the investigation of the binary system V,O, -Nb,O, (SCHADOW, OPPERMAUN et al.). Only the transport temperatures were kept much lower (973 + 873 K). An equimolar mixture NbCl,/CI, was used as the means of transport. The quantity of the means of transport was such that a pressure of 200 kPa was obtained at the mean transport temperature.For the spectrophotometric analysis of the chemically transported products the respective samples were triturated and melted in platinum crucible with sodium carbonate. After that, the melting cake was leached with water, the obtained niobium-hydroxide precipitate was filtered off and in the filtrate the vanadium was determined as yellow vanadium(I1) phosphotungstic acid.

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“…[38,39,40] Further examples for the successful crystallization of mixed-valent oxides with neighboring phases of close-lying composition are the Magnéli phases Ti n O 2n-1 (4 Յ x Յ 10) [41,42] and of the niobium oxides NbO x (2.000 Յ x Յ 2.500). [43,44,45] Crystallization of LaPO 4 was the first example for CVT of an oxide compound containing a complex anion.…”

Section: Binary and Multinary Oxidesmentioning

confidence: 99%

“…They realized that the composition of a binary compound AB x deposited at the sink is determined by the ratio of the fluxes J(B) and J(A) from the source to the sink (Equation (6)). (6) By linking the fluxes J(B) and J(A) of the individual components of the system and assuming that the net flux of the transport agent X will vanish, J(X) = 0, the stationarity relation ε (Equation (7)) was derived [75,43,44] . Thus, it was shown, how equilibrium calculations for source and sink region have to be linked to each other, without introducing some unjustified restrictions concerning the composition of the equilibrium solids.…”

Section: Cvt Of Phases With Homogeneity Rangementioning

confidence: 99%