Specific heat and thermal diffusivity of strontium barium niobate (Sr1−xBaxNb2O6) single crystals

The specific heat and thermal diffusivity of Sr1−xBaxNb2O6 (x=0.33 and 0.48) single crystals have been measured between 130 and 500 K, and the sound velocity has been measured at 295 K. At x=0.33 the specific heat shows a broad peak at 335 K, indicating the onset of a ferroelectric phase transition. The peak sharpens and shifts to about 383 K at x=0.48. A jump in the thermal diffusivity D is observed at the transition. Away from the transition, however, D is roughly independent of temperature. There is very little anisotropy in D, with the value along the a axis marginally higher than that along the c axis. Outside the transition region the phonon mean free path l is approximately constant, and has values of 5.1 and 5.6 Å, respectively, below and above the transition. The low values of D and l are due to the disorder arising from the random distribution of five Sr/Ba ions over six possible sites in a unit cell.