MULTIFUNCTIONAL CRYOGENIC SENSORS FROM N-BATIO3 CERAMICS HAVING STRONG NEGATIVE TEMPERATURE-COEFFICIENT OF RESISTANCE

Donor-doped n-BaTiO3 polycrystalline ceramics show a strong negative t emperature coefficient of resistivity below the orthorhombic-rhombohed ral phase transition point, from 10(2-3) Omega cm af 190 K to 10(10-13 ) Omega cm at less than or similar to 50 K, with thermal coefficient o f resistance alpha = 20-23% K-1. Stable thermal sensors for low-temper ature applications are realized therefrom. The negative temperature co efficient of resistivity region can be modified by substituting isoval ent ions in the lattice. Highly nonlinear current-voltage (I-V) curves are observed at low temperatures, with a voltage maximum followed by the negative differential resistance. The I-V curves are sensitive to dissipation so that cryogenic sensors can be fabricated for liquid lev el control, flow rate monitoring, radiation detection or in-rush volta ge limitation.