Optical properties of ferroelectric (Pb 1-x Ba x ) 5 Ge 3 O 11 for x=0 and 0.02

摘要: We report accurate measurements of the temperature dependence indices refraction [$n (T)$] in ferroelectric single crystals ${({\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{x})}_{5}{\mathrm{Ge}}_{3}{\mathrm{O}}_{11}$ for $x=0 \mathrm{and} 0.02$. Above transition ${T}_{c}$, $n (T)$ is linear with temperature. (It had been hoped that $x=0.02$ sample would show nonlinear results similar to those observed BaTi${\mathrm{O}}_{3}$.) Analyzing below ${T}_{c}$ terms quadratic electro-optic effect, ${[\ensuremath{\Delta}({n}^{\ensuremath{-}2})]}_{\mathrm{ij}}=\ensuremath{\Sigma}{k,l}^{}{g}_{\mathrm{ijkl}}{P}_{k}{P}_{l}$, reveals very large $g$ values, 20-100 times larger than Pb perovskites.