Phase Separation with Anisotropic Coherency Strain

Abstract

We consider the effects of anisotropic coherency strain (due to lattice mismatch) on phase separation in intercalation materials, motivated by the high-rate Li-ion battery material \fepo. Using a phase-field model coupled to elastic stresses, we analyze spinodal decomposition (linear instability of the homogeneous state) as well as nonlinear evolution of the phase pattern at constant mean filling. We consider fully anisotropic coherency strain and focus on the novel case of simultaneous expansion and contraction along different crystal axis, as in the case of \fepo, which leads to tilted, striped phase boundaries in equilibrium.