An inhomogeneously distorted state of the crystal structure of a Zn$_{0.95}$Fe$_{0.05}$Se cubic crystal

The structural state of a bulk Zn$_{0.95}$Fe$_{0.05}$Se cubic crystal grown by the chemical transport method from the gas phase has been investigated using thermal neutron diffraction at room temperature. It has been found that the measured neutron diffraction patterns of the crystal, in addition to structural Bragg peaks, contain a clearly identified system of superstructure reflections with the wave vector $\mathbf{k}$ = (1/3 1/3 1/3)2$\pi/a$ (where $a$ is the parameter of the cubic unit cell), which is interpreted as a clear evidence of the incipient transition state preceding the concentration phase transformation fcc $\leftrightarrow$ hcp. It has been shown that the resulting structural state includes an inhomogeneous microstrain field with the possible appearance of long-wavelength modulations based on the initial sphalerite structure.