Ba(Sr,Ti)O-3 material presents a remarkable property that lies in the possibility to change the permittivity by applying a DC electric field, i.e., BST is a tunable material. That makes BST a very interesting material for the development of reconfigurable devices in microelectronics. In this study, we focus our work on Ba(Sr, Ti)O-3 with Ba/Sr = 30/70, the films are deposited by radio-frequency magnetron sputtering on Al2O3 (0001). A buffer layer of TiOx is used to control the film orientation. The influence of this buffer layer on the dielectric properties, the interfaces quality with respect to the film thickness, and the temperature is analyzed. An increase of 30% of the relative permittivity was measured and a tunability of 50% was attained at 300 KV/cm. The dielectric measurements on BST/TiOx as a function of the temperature show a shift of the Curie temperature (T-c = -40 degrees C) in comparison to BST without TiOx layer (T-c = -80 degrees C). We demonstrate that the Curie temperature does not correspond to the maximum permittivity. The important stress measured on the films (930 MPa) could explain this behavior.