Pressure-induced critical behavior ofKMnF3close toPc=3.1 GPa: X-ray diffraction results

Abstract

The critical behavior of ${\mathrm{KMnF}}_3$ close to the pressure-induced cubic-to-tetragonal structural phase transition at ${\mathit{P}}_{\mathit{c}}$=3.1 GPa has been studied by single-crystal x-ray diffraction. The pressure dependence of a primary order parameter has been determined from superlattice Bragg intensities and was found to fulfill the power law Q=A(P-${\mathit{P}}_{\mathit{c}}$ ${)}^{\mathrm{\beta }}$. The transition with a small discontinuity of the intensities close to ${\mathit{P}}_{\mathit{c}}$ shows deviations from the classical behavior similarly as in the temperature-dependent transition at 186 K, where the domain structure considerably affects the values of the critical parameters. However, the pressure inhibits formation of large, single domains of definite orientation. Instead, increased width of diffraction profiles points to the appearance of numerous, narrow domains which may influence the character of the transition. © 1996 The American Physical Society.