Structural peculiarities of the intermediate phase in Zr-rich lead zirconate titanate

This paper presents the results of X-ray diffraction studies on a single crystal of lead zirconate titanate PbZr$_{0.993}$Ti$_{0.007}$O$_{3}$ in the region of existence of an intermediate ferroelectric phase. In addition to the known superstructure reflections of the M type $q_{M}=\{(1)/(2), (1)/(2), 0\}$ and the first-order satellite reflections $q_{M}+\{\delta,\delta,\delta\}$, unknown second-order satellites have been observed near $q_M$ and near the Bragg reflections. Structural model of regular system of antiphase domains is used for diffraction calculation. The model is shown to describe the first- and second-orders satellite reflections in the vicinity of $q_M$, but it cannot explain the appearance of satellites around the main Bragg peaks. A possible origin of the system of the superstructures observed in the intermediate phase is discussed.