Structural ordering upon annealing of europium molybdate subjected to pressure treatment

It has been found that treatment of europium molybdate single crystals under high uniform pressure leads to radical changes of the IR reflectance spectra of the samples. Instead of a series of narrow lines, which are characteristic of the spectrum of the initial crystal, the spectrum of the sample subjected to pressure treatment exhibits broad bands. As follows from the results of X-ray diffraction measurements, this transformation of the IR spectra is associated with the fact that, after pressure treatment, the sample represents an amorphous matrix with inclusions of nanocrystals of the high-pressure phase. In the IR spectra, the high-pressure phase manifests itself in the form of a new line at approximately 600 cm⁻¹. After annealing of the sample with an increase of the temperature from 100 to 400°C, the high-pressure phase disappears. A further increase of the annealing temperature to 550°C leads to the recovery of the crystal structure of the initial β′ phase of europium molybdate and to the appearance of lines corresponding to the α phase.