DEPENDENCE OF THE CHARACTERISTICS OF THE SHORT-RANGE ORDER IN ANODIC WO3 ON NUMBER OF COLORATION AND BLEACHING CYCLES

Ludmila Aleshina, Lubov Lugovskaya

KFTT, Petrozavodsk State University, pr. Lenina 33, 185640 Petrozavodsk, Russia.
E-mail: lugl@mainpgu.karelia.ru

Keywords: X-ray research, anodic tungsten oxides, hydrates, electrochromism, short-range order, computer simulation.

Thin films prepared from WO3 are electrochromic and this phenomenon is of interest in construction of WO3 film display devices. Brightest the effect is showed in amorphous tungsten oxides. Parameters of reaction depend on method of preparing of films and it's known electrochromic reaction at anodic films is faster than that at other ones.

X-ray research of structure of anodic tungsten oxides in the process of electrochromic coloration and bleaching of films in electrolyte has been carried out in this paper. The films were formed on mono- and polycrystalline W substrates. The number of switching cycles varied from 102 up to 105. Initial anodic films correspond to amorphous WO3 1/3 H2 O [1]. Changes of the x-ray diffraction pattern at the electrochromic process for the films formed on a polycrystalline tungsten [2] completely differ from those for samples on monocrystal. Electrochromic process results in various structural transformations for films on various substrates. That confirms big sensitivity this material to conditions of experiment.

At the increase of the number of switching cycles, amorphous WO3 1/3 H2 O transition to hydrate with bigger content of water WO3 2 H2O due to diffusion of H+ from electrolyte into the tungsten oxide lattice. Quantity of phases of these hydrates sharp grows up after 104 switching cycles.

Characteristics of the short-range order: interatomic distances rij and coordination numbers Nij were determined for films formed on monocrystalline substrate and were compared with crystalline phases of hydrates. At the increase of the number of coloration-bleaching cycles, redistribution of W-O distances and Nij takes place, but total conformity of films structure to hydrate WO3 1/3 H2 O keeps up to 104 cycles.

For the films, formed on polycrystalline tungsten, stored in laboratory conditions redistribution WO3 H2O and WO3 2 H2 O phase ratio has been observed.

Computer simulation of possible short-range order modifications in anodic amorphous tungsten trioxide at electrochromic process has been carried out.

  1. L.A.Aleshina, L.A.Lugovskaya. Crystallography Reports, 42, 2, (1997), 303-309
  2. L.A.Aleshina, S.V.Glazkova, L.A.Lugovskaya, V.P.Malinenko, A.D.Fofanov. Electrohimia, (1998) (in press)



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