OPTICAL-PROPERTIES OF RBTIOASO4 SINGLE-CRYSTAL

The longitudinal (LA) Brillouin back-scattering spectra along the [001 ] phonon direction have been measured over the temperature range 24-90 0 degrees C for RbTiOAsO4 (RTA) single crystal. As temperature increas es, the Rn;4 shows a strong frequency softening which persists above T -c similar to 794 degrees C, The acoustic soft mode begins to set in a t T similar to 300 degrees C for RTA. A broad growth was observed of b ath damping and susceptibility and is attributed to the dynamic order parameter fluctuations associated with a quadratic eta(2) mu-type coup ling (squared in order parameter and linear in strain). The refractive indices (n(x), n(y), n(z)) and the Cauchy equations were obtained as a function of wavelength (0.4-1.7 mu m). In addition, the LA sound vel ocity VLA and elastic constant C-33+(e(33)(2)/epsilon(33)(8)) were als o calculated at room temperature.