Structure-dielectric property relationship for vanadium- and scandium-doped barium strontium titanate

This paper reports the results of an investigation of the structure-property relationship of vanadium (donor) and scandium (acceptor) doped Ba_0.7Sr_0.3TiO₃. While V doping produces a fully miscible Ba_0.7Sr_0.3Ti_1-xV_xO₃ alloy, Sc doping results in an inhomogeneous microstructure with grains containing a Sc-doped Ba-rich shell and an undoped Sr-rich core. This results from a solution-precipitation process that works in combination with a thermodynamic driving force for the preferential segregation of Sc into Ba-rich regions. The Curie temperature (T_c) of Ba_0.7Sr_0.3TiO₃ decreases with increasing dopant concentration from a T_c of 40 °C for undoped material to 18 °C for 4 mol.% V and 22 °C for 4 mol.% Sc (i.e., Ba_0.7Sr_0.3Ti_0.96V_0.04O₃, Ba_0.7Sr_0.3Ti_0.96Sc_0.04O₃). Sc- and V-doped materials are found to have significantly reduced dielectric constants at their Curie temperature than their undoped counterpart. This is most evident for Sc doping, where a 4 mol.% concentration has a dielectric constant of 1000 at T_c, a factor of 12 times smaller than undoped Ba_0.7Sr_0.3TiO₃.