In situ Raman spectroscopy of A-site doped barium titanate

Raman spectroscopy has been used to study the ferroelectric tetragonal to paraelectric cubic phase transition Tc in undoped BaTiO3 (BT) and (Ba0.92A0.08)TiO3 [where A = Ca (BCT), Sr (BST), and Pb (BPT)]. In BT and BPT, mode characteristic of the tetragonal phase at 303 and 710 cm−1 persisted until >50 °C above Tc, indicating the presence of local dynamic polar clusters well above the displacive phase transitions, ∼ 120 and ∼ 149 °C, respectively. However, in BCT and BST, the Raman spectra exhibited only broad second order bands above Tc, suggesting that Ca and Sr, A-site dopants supress local dynamic polar clusters.