Chongyun Shao

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 A, 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.

Influence of F– on stark splitting of Yb3+ and the thermal expansion of silica glass

A local phosphate/fluoride environment of Yb3+ was created in silica glass using a multi-step method. The influence of F- on the Stark splitting of Yb3+ in Al3+/P5+/F- co-doped silica glass was studied at room-temperature, in addition to its effect on the thermal expansion performance of the glass matrix. The results indicate that Yb3+ ions in Al3+/P5+/F- co-doped silica glass have a larger Stark splitting energy of 2F7/2 compared to Al3+/P5+ co-doped silica glass. Moreover, a larger integrated absorption cross-section (34.58 pm2 × nm), stimulated emission cross-section (0.63 pm2), and better thermal expansion performance (1.3062 × 10−6 K- at 100 °C) are achieved in Al3+/P5+/F- co-doped silica glass. Finally, different function mechanisms of F- in silica and phosphate glasses were analyzed and the F-Si bond was used to explain the results in silica glass. The combination of low refractive index, large Stark splitting energy of 2F7/2, and small thermal expansion makes Al3+/P5+/F- co-doped silica glass a preferred material for large mode area fibers for high-power laser applications.A local phosphate/fluoride environment of Yb3+ was created in silica glass using a multi-step method. The influence of F- on the Stark splitting of Yb3+ in Al3+/P5+/F- co-doped silica glass was studied at room-temperature, in addition to its effect on the thermal expansion performance of the glass matrix. The results indicate that Yb3+ ions in Al3+/P5+/F- co-doped silica glass have a larger Stark splitting energy of 2F7/2 compared to Al3+/P5+ co-doped silica glass. Moreover, a larger integrated absorption cross-section (34.58 pm2 × nm), stimulated emission cross-section (0.63 pm2), and better thermal expansion performance (1.3062 × 10−6 K- at 100 °C) are achieved in Al3+/P5+/F- co-doped silica glass. Finally, different function mechanisms of F- in silica and phosphate glasses were analyzed and the F-Si bond was used to explain the results in silica glass. The combination of low refractive index, large Stark splitting energy of 2F7/2, and small thermal expansion makes Al3+/P5+/F- co-doped silica glass a pr...