Effect of Mn doping on the acoustic and vibrational behaviors of lead-free piezoelectric (Na1/2Bi1/2)TiO3-xBaTiO3 single crystals

The acoustic and vibrational properties of Mn-doped (Na1/2Bi1/2)TiO3-xBaTiO3 with x = 0.05 were investigated by using Brillouin and Raman spectroscopies and compared with those of undoped crystals. The mode frequency and the half width of the Brillouin doublet of the longitudinal acoustic mode showed more drastic changes near the dielectric maximum temperature compared to the broad and diffused changes of the undoped crystals, which indicates that Mn-doping induces polar domains larger than the typical polar nanoregions formed in undoped counterpart. The acoustic anomalies were most pronounced along the <100> direction suggesting that the polarization fluctuations are anisotropic and largest along this direction. Temperature dependence of Raman spectra showed that there are two characteristics temperatures where mode splitting occurs due to local symmetry changes. The high-temperature anomaly was associated with the changes in the acoustic properties, while the low-temperature mode splitting was related to the dielectric anomaly near depolarization temperature.