Optical properties of epitaxial Ba$_{1-x}$Sr$_{x}$TiO$_{3}$ films on MgO(100) substrates

We present optical properties of Ba$_{x}$Sr$_{1-x}$TiO$_{3}$ (0.0 $\le \quad x$ $\le $ 1.0) films grown epitaxially by pulsed laser deposition (PLD) on MgO (100) substrates. Nominal thickness of the grown layers was 5000{\AA}. Room-temperature pseudodielectric function spectra $<\varepsilon >$ = $<\varepsilon _{1}>+i<\varepsilon _{2}>$ of the alloys were measured by spectroscopic ellipsometry from 1.5 to 5.0 eV. The spectra obtained exhibit two critical-point structures at $\sim $ 4.2 and $\sim $ 4.8 eV as well as the fundamental absorption edge (the $E_{0})$ below 4 eV. Analysis of second energy derivatives calculated numerically from the measured date yielded critical-point energies of interband transitions. Dependence of critical-point energies on alloy composition is discussed.