Investigation of a ferroelastic phase transition in NdP514 by EPR study of Gd3+ center

Abstract
The ferroelastic phase transition between P21/c and Pncm structure of GdxNd1−xP5O14 is analyzed by EPR spectra, and the dependence of the resonance spectrum is studied from 77 to 421 K. It is shown that the orientation of the principal axis of the classical D tensor is mainly related to the spatial symmetry of the crystal by a rotation angle, and its temperature dependence is analyzed using the Landau model of phase transitions. Alternatively, the critical exponent of the order parameter near the phase transition has been found to be β = 0.33.