The Vibrational Spectra of NH4VO3 at Elevated Temperatures and Pressures

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Abstract
Results obtained from the vibrational spectra of NH4VO3 and its deuterated analogues show that at least two types of hydrogen bond interactions can be identified at am bient conditions. In accordance with the structural data on NH4VO3 (F. C. Hawthorne and C. Calvo, J. Solid State Chem. 22, 157 (1977)) these interactions are assigned to normal, strong hydrogen bonds and weaker bifurcated ones, respectively. The temperature dependence of some of the N -H bands indicates that the normal hydrogen bonds decrease in strength with increasing temperatures, while the bifurcated ones tend to increase in strength. The NH4 + ions do not show fluxional behaviour at ambient conditions and even the bifurcated hydrogen bonds are of the type that is dominated by acceptor strength of the anions and not by a volume effect. The Ram an active NH4 + vibrations are very weak compared to the V - O modes and could not all be observed in the highpressure diamond anvil cell. The temperature dependence of the V - O Ram an active modes suggests that changes in the crystals of NH4VO3 brought about by the application of heat mainly involve the O -V -O angles, while pressure changes are mostly accommodated by changes in the V -O bridging bonds and O -V -O bridging angles.

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