Sr- and Ti-site substitution, lattice dynamics, and octahedral tilt transition relationship in SrTiO 3:Mn ceramics

Abstract

SrTiO 3:Mn ceramics, prepared according to the chemical formulae Sr 1– x Mn x TiO 3 and SrTi 1– y Mn y O 3, 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 SrTiO 3, and to ascertain their different lattice site locations. The polar soft mode of the incipient ferroelectric SrTiO 3 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 SrTiO 3.