Change from a bulk discontinuous phase transition in V2H to a continuous transition in a defective near-surface skin layer

Modelling Simul. Mater. Sci. Eng. 8 (2000) 269-275.

J Trenkler1,5, H Abe1,6, P Wochner2, D Haeffner3, J Bai4, H D Carstanjen2 and S C Moss1

1 Department of Physics, University of Houston, Houston, TX 77204-5506, USA
2 Max-Planck-Institut f?r Metallforschung, D-70569 Stuttgart, Germany
3 Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439-4815, USA
4 Oak Ridge Associated Universities, Oak Ridge, TN 37831, USA

5Present address: Max-Planck-Institut f?r Metallforschung, D-70569 Stuttgart, Germany.
6Present address: National Defense Academy, Hashirimizu, Yokosuka 239-8686, Japan.

Received 27 October 1999, accepted for publication 13 April 2000

Using high- and low-energy x-ray scattering techniques, we have studied the effect of defects on the beta1-beta2 phase transition in V2H. Since we earlier observed two length scales in this crystal, we focus here exclusively on either the pure bulk or the defective skin layer, which is several micrometres thick. While we found a strong and narrow discontinuous transition in the bulk, there is a continuous transition in this defective skin layer in which the mosaic spread decreases with depth. We suggest that the strain field associated with the change of the mosaic spread most likely prompts the conversion of the order of the phase transition.
 

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Department of Materials Science and Engineering
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