Phase transformations of ammonium tungsten bronzes

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Abstract

This article discusses the formation and structure of ammonium tungsten bronzes, (NH4)xWO3-y. As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and 1H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO3. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the cell parameters of α-HATB and h-WO3, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO3 transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the structure of this phase-called β-HATB, (NH4)0.001WO2.79-was hexagonal.

Original languageEnglish
Pages (from-to)707-716
Number of pages10
JournalJournal of Thermal Analysis and Calorimetry
Volume98
Issue number3
DOIs
Publication statusPublished - Dec 2009

Fingerprint

Tungsten
Bronze
bronzes
Ammonium Compounds
phase transformations
tungsten
Phase transitions
Differential thermal analysis
thermal analysis
X ray photoelectron spectroscopy
Nuclear magnetic resonance
Atoms
Oxidation
nuclear magnetic resonance
Scanning electron microscopy
oxidation
scanning electron microscopy
cells
atoms

Keywords

  • H-MAS NMR
  • Ammonium tungsten bronze
  • Annealing
  • Crystal structure
  • Phase transformations
  • Raman
  • TG/DTA-MS
  • XPS
  • XRD

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Condensed Matter Physics

Cite this

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title = "Phase transformations of ammonium tungsten bronzes",
abstract = "This article discusses the formation and structure of ammonium tungsten bronzes, (NH4)xWO3-y. As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and 1H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO3. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the cell parameters of α-HATB and h-WO3, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO3 transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the structure of this phase-called β-HATB, (NH4)0.001WO2.79-was hexagonal.",
keywords = "H-MAS NMR, Ammonium tungsten bronze, Annealing, Crystal structure, Phase transformations, Raman, TG/DTA-MS, XPS, XRD",
author = "Szil{\'a}gyi, {Imre Mikl{\'o}s} and I. Saj{\'o} and P. Kir{\'a}ly and G. T{\'a}rk{\'a}nyi and A. T{\'o}th and A. Szab{\'o} and K. Josepovits and J. Madar{\'a}sz and G. Pokol",
year = "2009",
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T1 - Phase transformations of ammonium tungsten bronzes

AU - Szilágyi, Imre Miklós

AU - Sajó, I.

AU - Király, P.

AU - Tárkányi, G.

AU - Tóth, A.

AU - Szabó, A.

AU - Josepovits, K.

AU - Madarász, J.

AU - Pokol, G.

PY - 2009/12

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N2 - This article discusses the formation and structure of ammonium tungsten bronzes, (NH4)xWO3-y. As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and 1H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO3. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the cell parameters of α-HATB and h-WO3, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO3 transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the structure of this phase-called β-HATB, (NH4)0.001WO2.79-was hexagonal.

AB - This article discusses the formation and structure of ammonium tungsten bronzes, (NH4)xWO3-y. As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and 1H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO3. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the cell parameters of α-HATB and h-WO3, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO3 transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the structure of this phase-called β-HATB, (NH4)0.001WO2.79-was hexagonal.

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