Single crystals (Na$_{1/2}$Bi$_{1/2}$)(Mg$_{1/3}$Nb$_{2/3}$)O$_3$: synthesis, structure, properties

Single crystals (Na$_{1/2}$Bi$_{1/2}$)(Mg$_{1/3}$Nb$_{2/3}$)O$_3$ (NBMN) of perovskite with disordering in A and B sublattices were grown for the first time by spontaneous crystallization. The space group of the NBMN crystal ($Pm\bar3m$, $a$ = 3.954 $\pm$ 0.001 $\mathring{\mathrm{A}}$) and the value of the refractive index ($n$ = 2.31 $\pm$ 0.02, $\lambda$ = 0.633 $\mu$m) at room temperature were determined. Anomalies were found in the temperature dependences of the dielectric response in NBMN: frequency-dependent maxima of dielectric losses in the temperature range 110 K, characteristic of the transition to a relaxor ferroelectric state and a frequency-independent anomaly in the vicinity of 300 K. The existence of thermally activated conduction behavior with an activation energy of 0.66 eV at temperatures above 590 K is shown. The measurement of dielectric hysteresis by the PUND method revealed the existence of switchable polarization at 77 K. The analysis of the dielectric properties makes it possible to attribute the NBMN crystal to the family of relaxor ferroelectrics with a perovskite structure.