Anomaly in the infrared active phonon modes and its relationship to the dielectric constant of (Ba1-xSrx)(Mg1/3Ta2/3)O-3 compound

A characteristic change in the dielectric properties with A-site substitution is known in complex perovskite compounds, (Ba, Sr)(B', B '')O-3, which are expected to be applied to dielectric resonators. Recently, a phase transformation upon tilting of oxygen octahedra has been found in some of the compounds. However the oxygen tilting transformation has not been considered to affect the dielectric constant explicitly. To clarify the relationship between the dielectric constant and the phase transformation, dielectric properties of a solid-solution system, (Ba1-xSrx)(Mg1/3Ta2/3)O-3, have been studied. The origin of the dielectric constant, the polar mode of the lattice vibration, has been investigated using infrared reflectivity spectroscopy and the Kramers-Kronig analysis. It was found that the phase transformation due to the tilting of the oxygen octahedra clearly affects polar phonon modes of the compound. The origin of the change in the dielectric properties with Sr concentration is discussed referring to the behavior of polar phonon modes.