The negative terminal capacitance at high frequencies (usually f much
greater than 10(6) Hz) in ZnO-Bi2O3-based varistor systems is attribut
ed to two possible sequential and/or combined sources: (a) piezoelectr
ic grain resonance; and (b) electrode-lead or contact impedance. These
sources are examined using a variation in the geometry of the varisto
r material and its electrode-lead configuration. The approximate value
s of the resonating parameters, designated by an equivalent series lum
ped inductance-capacitance-resistance (L(r)-C(r)-R(r)) circuit in para
llel with materials' characteristic capacitance C0, are extracted empl
oying lumped parameter/complex plane analysis technique for these ac e
lectrical data. At the resonating frequency, the lumped reactance of t
his series circuit nullifies yielding a resistance R(r) referred to th
e lumped ZnO grains.