Raman Spectroscopy of the Thermoelectric Sr$_{0.61}$Ba$_{0.39}$Nb$_{2}$O$_{6}$

Strontium Barium Niobate (SBN) has recently been shown by Lee et al. [1] to exhibit high thermoelectric power factors at temperatures above 500 K when it has been highly reduced. To determine the effects of reduction on the phonons, the Raman spectra of \textit{unreduced} and \textit{reduced} SBN have been measured at room temperature along the axis of polarization (\textbf{\textit{c}}-axis) and perpendicular to it (\textbf{\textit{a}}-axis). The Raman features of the \textit{unreduced} crystal are found to be very broad and overlapping. In particular, a strong Lorentzian central (quasi-elastic) peak extending out to 400cm$^{-1}$ is observed for light polarized along the \textbf{\textit{a}} axis. By contrast and unexpectedly in the \textit{reduced} crystal, thought to be more disordered, well resolved Raman peaks are observed, particularly at low frequencies. Also in the \textit{reduced} crystal, the central peak is much suppressed and narrower, but a new peak appears at 1000cm$^{-1}$ for both \textbf{\textit{c}} and \textbf{\textit{a}} polarizations. In addition, the high frequency peaks (\textgreater 200 cm$^{-1})$ appear to broaden and to shift toward higher frequencies. High temperatures results may be available at the time of the conference. \\[4pt] [1] S. Lee, J.A. Block, S. Trolier-McKinstry and C. Randall, J. Europ. Ceram. Soc. v.32, p.3971 (2012)