Sr- and Ti-site substitution, lattice dynamics, and octahedral tilt transition relationship in SrTiO3:Mn ceramics

SrTiO3:Mn ceramics, prepared according to the chemical formulae Sr1-xMnxTiO3 and SrTi1-yMnyO3, are studied by Fourier transform infrared and time-domain terahertz spectroscopy in the temperature range of 10-300 K to support the incorporation of Mn ions into the perovskite lattice of SrTiO3, and to ascertain their different lattice site locations. The polar soft mode of the incipient ferroelectric SrTiO3 is found to be hardened in the whole temperature range by the substitution of Mn ions on Ti sites, and only in the low-temperature range by the Sr site substitution. Activation of the mode, associated with the R point condensation of the Brillouin zone due to the doubling of the unit cell by antiphase rotations of the O-octahedra below the structural transition temperature T-a, shows that the substitution of Mn ions on the Sr sites increases T-a, whereas the Ti-site substitution suppresses T-a with respect to the undoped SrTiO3. (C) 2009 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.