Ferroelectrical and Dielectric Properties of BaTiO$_{3}$/Ba$_{(1-x)}$Sr$_{x}$TiO$_{3}$ Superlattices

Artificially designed superlattices (SL) composed of alternate layers of BaTiO$_{3}$ (BT) and SrTiO$_{3}$ (ST) have attracted interests due to the possibility of producing superior and new functional properties, which are attractive for device applications. We have fabricated SL of BT/Ba$_{(1-x)}$Sr$_{x}$TiO$_{3}$ (BST) with x = 0, 0.3, 0.4, 0.5, 0.6, 0.7, 1, utilizing multi-target by pulsed laser deposition technique. The modulation period ($\Lambda )$ in all SL was $\Lambda $= 80 {\AA} and the total thickness of each SL films were 600 nm. The x-ray diffraction revealed well oriented (00l) perovskite structure and the so-called satellite peaks. The polarized Raman spectra showed the substantial transformation of the ferroelectric E(1TO) soft mode, depending of the ratio of Ba/Sr in BST layer. The dielectric constant of SL showed linear frequency dispersion above of 20 kHz, and their values are in the range of 400 to 900 at 1 kHz, while the tangent loss values were below to 0.1 at 1 kHz. Well defined ferroelectric loop was observed in all the SL at different frequencies (1 kHz-10 kHz), with remanent polarization (2P$_{r})$ 10 $\mu $C/cm$^{2}$. Improvement in saturation in the ferroelectric loop was observed with increase of Ba composition in BST layer. All these superlattices show very low leakage current far above its coercive field.