Ein neues Syntheseverfahren für die Wolframbronze Cs_0,29WO₃

Abstract

Bei der Reaktion von WO3 in einer Caesiumiodid‐Schmelze bei 700°C entsteht die hexagonale Wolframbronze Cs0.29WO3 in Form schwarzer, hexagonal‐prismatischer Kristalle. Ihre Struktur wurde durch Röntgenbeugung bestimmt (399 beobachtete unabhängige Reflexe, R = 5,8%). Kristalldaten: a = 741,2(3), c = 760,0(5) pm, Raumgruppe P6322, Z = 6. Es handelt sich um die bekannte Struktur der hexagonalen Wolframbronzen mit Wolframatomen, die aus den Oktaedermitten um 11,9 pm herausgerückt sind und mit drei verschiedenen WO‐Bindungslängen (198, 191, 187 pm). Die WO6‐Oktaeder sind leicht gegeneinander verkippt.

Oxygen vacancies and pseudo Jahn‐Teller destabilization in cesium‐doped hexagonal tungsten bronzes

“…The emergence of ( h0l ) l :odd reflections indicates a transition of the crystal symmetry from P6 3 /mcm to P6 3 22 . This observation in Cs 0.25 WO 3− y and Cs 0.20 WO 3− y is consistent with PMH1992 that studied Cs 0.29 WO 3 . On decreasing alkali content, alkali HTBs decompose to HTB + WO 3 at x ≤ 0.19 according to the phase diagram, whereas in the present study the peaks due to WO 3 , WO 2.90 , and WO 2.92 are clearly observed at x = 0.20.…”

“…In the literature, other compositions of HTBs have also been analyzed on the basis of P6 3 /mcm by Labbé et al on Rb 0.30 WO 3 , by Kihlborg and Hussain (called KH1979 hereafter) on Cs 0.32 WO 3 , and by Oi et al (called OKK1993 hereafter) on Cs 0.30 WO 3 , respectively. On the other hand, Pye and Dickens utilized neutron diffraction to assign a different space group P6 3 22 (; No.182) on K 0.26 WO 3 , and Prinz et al (called PMH1992 hereafter) similarly assigned P6 3 22 through the x‐ray work on Cs 0.29 WO 3 .…”

“…Designated times are durations in a 1%H 2 –N 2 gas flow at 550°C for Cs 0.32 WO 3− y , and designated x values are nominal content of Cs with reduction time 1 h at 550°C. KH 1979: Kihlborg and Hussain, OKK 1993: Oi, Kishimoto and Kudo, PMH 1992: Prinz, Muller, and Ha‐Eierdanz, AA 2012: Adachi and Asahi [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Detailed structural analysis of Cs x WO 3 using XRD‐Rietveld method has been reported in the past by three groups, KH1979, PMH1992, and OKK1993, for samples of different synthesis methods. Tungsten bronzes are reported as synthesized first by Berzelius for H x WO 3 in 1816 and Wohler for Na x WO 3 in 1824, respectively, by heating materials in a hydrogen gas stream (GFR method).…”

Vibrational properties of ferroelectric hexagonal tungsten bronzes ABxW3−xO9, where A = K, Rb, Cs and B = Nb, Ta, Zr, Cr

“…Since, however, the distortion from the hexagonal structure is small, we can use in the vibrational analysis the results of the x-ray investigation performed by Yanovskii et al 1 According to this study, the high-temperature phase is most likely described by the space group P6 3 22 and the primitive cell contains two AB x W 3 x O 9 units (26 atoms). 1 The same crystal structure was found 15,16 for K 0.26 WO 3 and Cs 0.29 WO 3 . The results of the factor group analysis are presented in Table 2.…”