Investigation into the evolution of the structure of K1−x LixTa1−y NbyO3 single crystals under variations in temperature

The evolution of the structure of K1−x LixTa1−y NbyO3 single crystals with x = 0.001, y = 0.026, and 1900 ppm Cu (KLTN277) and with x = 0.0014 and y = 0.024 (KLTN123), which exhibit an extremely high permittivity (up to 4 × 105 in the quasi-static regime for the KLTN277 crystal), is investigated in the range from room temperature to 20 K. It is demonstrated that, upon cooling to the lowest temperatures, both crystals retain their cubic structure, but the lattice parameters pass through a minimum at the temperature of the observed anomalies of the dielectric response (∼50 K). In the neutron diffraction pattern of the KLTN123 sample, satellites appear in the vicinity of the (hhh) reflections at temperatures below ∼50 K. These satellites can be associated with the nucleation of the rhombohedral phase.