Electrical properties of Ba0⋅7Bi0⋅3Fe0⋅9Sn0⋅1O3–BaCo0⋅02II$^{\mathrm{II}}_{0\cdot 02}$Co0⋅04III$^{\mathrm{III}}_{0\cdot 04}$Bi0⋅94O3 thick film thermistors with wide-range adjustable parameters