The specific heat and thermal diffusivity of Sr1minus;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. Atx=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 atx=0.48. A jump in the thermal diffusivityDis observed at the transition. Away from the transition, however,Dis roughly independent of temperature. There is very little anisotropy inD, with the value along theaaxis marginally higher than that along thecaxis. Outside the transition region the phonon mean free pathlis approximately constant, and has values of 5.1 and 5.6 Aring;, respectively, below and above the transition. The low values ofDandlare due to the disorder arising from the random distribution of five Sr/Ba ions over six possible sites in a unit cell.
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