Synthesis of cubic and tetragonal Ba₂SmTaO₆ and their optical properties after Sr doping

Ba_2–xSr_xSmTaO₆ has attracted great attention due to its excellent dielectric performance and abundant crystal structures. Recent studies find the reflectance of Sr–doped Ba₂SmTaO₆ (Ba_2–xSr_xSmTaO₆) significantly changes with the transition between its varied phases, indicating the potential applications in optical sensors. However, its phase transition temperature (T_t) and the preparation process are not clear. In this work, the T_t between the cubic and tetragonal phases of Ba₂SmTaO₆ was firstly confirmed to be 533 K using self–consistent phonon theory (SCP). Combining the experimental and calculation methods, we found that the cubic and tetragonal phases of Ba_2–xSr_xSmTaO₆ can be obtained by reacting at 1200 °C for 8 h and 1200 °C for 96 h with a low cooling rate of 2 °C/min, using the solid state reaction method, respectively. With characterizing the reflectance of different phase structures Ba_2–xSr_xSmTaO₆, the largest reflectance difference between the tetragonal phase and cubic phase was found to be 59.22% at a wavelength of 1064 nm (wavelength commonly used in laser emitters) when x is 1.5, indicating it has great potential using in the optical sensor area. This research provides a guidance for the preparation of complex perovskite with different crystal structures of similar A₂BB'O₆ structure materials and is of great significance for the application of Ba_2–xSr_xSmTaO₆ in optical sensors.