High-temperature behavior of vanadyl pyrophosphate image

image has been studied at high temperatures by in situ X-ray powder diffraction in an inert atmosphere. Lattice parameters indicate an anisotropic thermal expansion up to image, followed by an approximately isotropic expansion up to image. It is proposed that image is the temperature of a second-order phase transition between the known room temperature form with space group image and a high-temperature form with space group Pcab. Above image a minority phase develops in the sample that was identified as the image containing compound image, while the anisotropic expansion along image suggests that stoichiometric image transforms into image with interstitial oxygen located between the layers. With an onset at image all of the image transforms into image.