Investigations on the Quasi‐binary Subsystem VNb₉O₂₅Nb₂O₅

Abstract

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.

Thermal analysis and crystal growth of doped Nb2O5

“…This observation is in agreement with other authors[20,36,37,38,39]. Schadow et al were able to isolate only one stable compound by studying the system using chemical transport reactions[20,36]. The phase diagram constructed on the basis of these results shows correspondingly great agreement with that of the present work.…”

“…These results cannot be confirmed in the present work, and only VNb 9 O 25 was found. This observation is in agreement with other authors[20,36,37,38,39]. Schadow et al were able to isolate only one stable compound by studying the system using chemical transport reactions[20,36].…”

High-Rate Long-Life Pored Nanoribbon VNb9O25 Built by Interconnected Ultrafine Nanoparticles as Anode for Lithium-Ion Batteries

“…23−26 As one of the thermodynamically stable phase in the V 2 O 5 -Nb 2 O 5 system, VNb 9 O 25 is the focus of the research for developing vanadium niobium oxides. 27 VNb 9 O 25 was first synthesized in 1960 via a simple solid state reaction (SSR). 28 From 1985, sol−gel synthesis becomes a widespread route to prepare VNb 9 O 25 .…”

“…Vanadium niobium oxides are widely studied due to extensive application in catalysis and electrochemical fields. − As one of the thermodynamically stable phase in the V 2 O 5 -Nb 2 O 5 system, VNb 9 O 25 is the focus of the research for developing vanadium niobium oxides . VNb 9 O 25 was first synthesized in 1960 via a simple solid state reaction (SSR) .…”