Use of Raman spectroscopy to determine the site occupancy of dopants in BaTiO₃

Chemical doping is one of the major methods by which the properties of BaTiO₃ are modified to induce various device characteristics. Doping strategies are generally separated into iso- and alio-valent (donors and acceptors) and into A- and B-site species within the perovskite structure. The A_1g octahedral breathing mode at ∼800 cm⁻¹ in BaTiO₃ is Raman inactive for compositions with single B-site species. However, this mode becomes Raman active if more than one B-site species is present, including titanium vacancies, V_T′′′′. Moreover, the relative intensity of the A_1g breathing mode is qualitatively related to the concentration of the species replacing Ti in the B-site. This article illustrates some clear cases where the A_1g octahedral breathing mode can be utilized to verify the site occupancy of dopants in BaTiO₃ when used in conjunction with more conventional indirect methods such as x-ray diffraction (Vegard’s Law) and dielectric measurements as a function of temperature.