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 Ba0.7Sr0.3TiO3. While V doping produces a fully miscible Ba0.7Sr0.3Ti1−xVxO3 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 (Tc) of Ba0.7Sr0.3TiO3 decreases with increasing dopant concentration from a Tc of 40 °C for undoped material to 18 °C for 4 mol.% V and 22 °C for 4 mol.% Sc (i.e., Ba0.7Sr0.3Ti0.96V0.04O3, Ba0.7Sr0.3Ti0.96Sc0.04O3). 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 Tc, a factor of 12 times smaller than undoped Ba0.7Sr0.3TiO3.