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Microscopy and Microanalysis 20 (2014) 1453-1462

Periodic cation segregation in Cs_{0.44}[Nb_{2.54}W_{2.46}O_{14}] quantified by high-resolution scanning transmission electron microscopy

by
Markus Heidelmann, Juri Barthel, Gerhard Cox, and Thomas Weirich

The atomic structure of Cs_{0.44}[Nb_{2.54}W_{2.46}O_{14}] closely resembles the structure of the most active catalyst for the synthesis of acrylic acid, the M1 phase of Mo_{10}V_{2}^{4+}Nb_{2}TeO_{42-x}. Consistently with observations made for the latter compound, the high-angle electron scattering signal recorded by scanning transmission electron microscopy shows a significant intensity variation, which repeats periodically with the projected crystallographic unit cell. In the present study, the occupation factors for the individual mixed Nb/W atomic columns are extracted from the observed intensity variations. For this purpose, experimental images and simulated images are compared on an identical intensity scale, which enables a quantification of the cation distribution. According to our analysis specific sites possess low tungsten concentrations of 25%, whereas other sites have tungsten concentrations above 70%. These findings allow us to refine the existing structure model of the target compound, which has until now described a uniform distribution of the niobium and tungsten atoms in the unit cell, showing that the similarity between Cs_{0.44}[Nb_{2.54}W_{2.46}O_{14}] and the related catalytic compounds also extends to the level of the cation segregation. dimensions.

Further reading:

Markus Heidelmann, Juri Barthel, Gerhard Cox, and Thomas Weirich: Periodic cation segregation in Cs_{0.44}[Nb_{2.54}W_{2.46}O_{14}] quantified by high-resolution scanning transmission electron microscopy, Microscopy and Microanalysis 20 (2014) 1453-1462.

   
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