Composition dependence of the lattice vibrations in Srn+1TinO3n+1 Ruddlesden–Popper homologous series

Room-temperature infrared reflectivities, time-domain THz transmission spectra and micro-Raman spectra of ceramics in the Ruddlesden–Popper homologous series, Srn+1TinO3n+1 (where n=1, 2, 3, 4, ∞), were studied. Increasing the number of perovskite layers (n) in the crystal system resulted in higher polarizability of the lattice and softening of the lowest frequency phonon mode, which is responsible for the observed increase in microwave permittivity, dielectric loss and temperature coefficient of resonance frequency with n. Although the infrared and Raman spectra revealed many defects in the ceramics (e.g. second phases and stacking faults), the extrapolation of experimental submillimetre dielectric data to the microwave region showed no dielectric dispersion below the phonon frequencies and prevailingly an intrinsic origin of losses in the microwave region in almost all samples (except for Sr5Ti4O13).