Thmse 600

The crystal plate was inserted in a compact temperature controller (THMSE600 or TS1500, Linkam, Tadworth, UK) which was put under a modified microscope (BX-41, Olympus, Tokyo, Japan) for backscattering measurements. The Brillouin scattering spectrum was measured by using a conventional tandem six-pass Fabry-Perot interferometer (TFP-1 or TFP-2, JRS Co., Zürich, Switzerland) and a diode-pumped solid state laser (Excelsior 532-300, Spectra Physics, Santa Clara, CA, USA). The wavelength of the laser was 532 nm, operated at the power of tens of mW. The unpoled NBT-5%BT is pseudo-cubic without any measurable birefringence. The polarization direction of the incident laser beam was along the pseudo-cubic [100] direction. The free spectral range of the interferometer was set to 75 GHz for probing the acoustic modes. A conventional photon-counting system combined with a multichannel analyzer (1024 channels) was used to detect and average the signal. All the Brillouin spectra were measured with increasing temperature. The details of the experimental setup can be found elsewhere [39 (link),40 (link)].

All chemicals were commercially purchased and were used without further purification. Powder X-ray diffraction (PXRD) patterns were recorded using a Bruker D8 ADVANCE X-ray powder diffractometer (Cu K_α, λ = 1.54184 Å). Thermogravimetric analyses (TGA) were performed using a TA Q50 system at a heating rate of 10 K min−¹ under a nitrogen atmosphere. Differential scanning calorimetry (DSC) measurements were performed by heating and cooling the powdered sample at a rate of 10 K min⁻¹ on a TA DSC Q2000 instrument. The dielectric measurements were carried out on a TH2838 impedance analyzer at frequencies from 5 kHz to 2.0 MHz, with an applied voltage of 1.0 V and a temperature sweeping rate of 3 K min⁻¹ approximately in the range of 100–440 K in a Mercury iTC cryogenic environment controller of Oxford Instrument. The pressed-powder pellets were fixed by two magnetic sheets acting as electrodes. Variable-temperature polarization microscopy observations were carried out on a polarizing microscope OLYMPUS BX41-P equipped with a Linkam cooling/heating stage THMSE 600. The temperature was stabilized to an accuracy of ±0.1 K. The SHG effect was measured using an XPL1064-200 instrument at a heating/cooling rate of 2 K min⁻¹.