Nuclear resonant scattering evidence of the phase co-existence during structural phase transformation in [Fe(H2O)6](ClO4)2

The phase transition associated with orbital-ground-state inversion of high-spin Fe2+ in [Fe(H2O)6](ClO4)2 was studied with nuclear resonant forward scattering of synchrotron radiation (SR). The sudden change in the 57Fe2+ quadrupole interaction results in a change of the quantum-beat frequencies. Quantum-beat patterns taken at the phase transition of [Fe(H2O)6](ClO4)2 are in accordance with mainly coherent rather than with incoherent sums of the scattering amplitudes of the high- and low-quadrupole-interaction phases, a fact supporting the real co-existence of the two phases.