Mössbauer effect studies of the phase transition process in europium pentaphosphate

Mössbauer spectra of europium pentaphosphate are measured at various temperatures (126 to 200 °C). Some Mössbauer parameters, such as isomer shift, electric quadrupole splitting, and asymmetry parameter of the EFG at ¹⁵¹Eu nuclei are derived from the experimental spectra. The lattice parameters of the crystal are determined at several temperatures. The experimental results indicate that the crystal structure of europium pentaphosphate changes from monoclinic to orthorhombic. All of the temperature dependences of the Mössbauer parameters provide evidence of a phase transition of the crystal. The phase transition temperature can be determined from the curve of the asymmetry parameter of EFG versus temperature to 165 °C.