Growth and Inelastic Light Scattering Studies on Sr2Nb2O7 Single Crystal

Abstract

A crack-free and high structural quality Sr2Nb2O7 single crystals are grown by the optical float zone method using optimized growth parameters. The Laue pattern confirms the single crystalline nature of the grown crystal. Temperature-dependent Raman and Brillouin light scattering studies reveal a significant shift in phonon modes across normal to incommensurate phase transition (Tn-in) which occurs ≈488 K. In the temperature range from 900 down to 500 K, two optical phonon modes ≈63 (B1 mode) and 54 cm−1 (A1 mode) are observed. The frequency of A1 mode strongly decreases with an increase in temperature above the Tn-in while the frequency of this mode almost remains constant below the Tn-in. In contrast, the frequency of B1 phonon mode is found to increase with temperature in the range of 500–900 K but it does not display a significant shift below the phase transition temperature. In addition, in the in-commensurate phase (T< 488 K), a new optical phonon mode (M1) at ≈35 cm−1 also begins to appear and exhibits strong stiffening behavior with an increase in temperature in the range of 300–488 K. Moreover, the anomalous behavior of the acoustic phonon across Tn-in are further probed using Brilliouin scattering. Longitudinal acoustic phonon mode at 41 GHz exhibits a strong change in slope near Tn-in. In addition, the transverse acoustic modes at 28.6 and 22.4 GHz also exhibit strong anomalies with minimum frequency near Tn-in. The inelastic light scattering studies provide valuable information on the phase transition.