Specific heat anomalies at 37, 105 and 455 K in SrTiO3:Pr

Strontium titanate modified with praseodymium was investigated by means of a combination of synchrotron x-ray diffraction and thermal analysis at high and low temperatures. The x-ray diffraction data obtained at room temperature revealed a breakdown of the cubic symmetry via the (002)/(200) split peaks. Thus, both the diffuse anomaly in the DTA measurement and the permittivity peak indicate that cubic symmetry is reached at about 455 K. At low temperatures, the specific heat reveals two anomalies at similar to 105 and similar to 37 K. Both anomalies were sensed for the phonon part of the total specific heat. The soft acoustic phonon modes are responsible for the plateau region in the specific heat at about 105 K, which is slightly larger for undoped samples. Furthermore, a clear anomaly at similar to 37 K in the specific heat is sensed by the Pr impurity in the host lattice of SrTiO3 and a minimum in the temperature dependence of the Debye temperature, Theta(D) around 30 K is observed. A maximum in the CT-3 versus T-2 curve seems to indicate that the low-lying vibrational modes dominate at 37 K.