Piezoelectric and ferroelectric properties of polyurea-5 thin films prepared by vapor deposition polymerization

Submicron films of aliphatic polyurea-5 were synthesized by vapor deposition polymerization. The structure of films depended on the partial pressure ratio of evaporated monomers. Excess of diamine monomer over diisocyanate monomer yielded lower crystalline structure, to be poled easier at low temperatures. The maximum value of the piezoelectric stress constant e(31) was 10 m C/m(2), twice that of polyurea-9. The pyroelectric constant was about 15 mu C/m(2) K. Ferroelectric D-E hysteresis was observed. Three relaxations were observed for the temperature dependence of the elastic constant, the dielectric constant, and the piezoelectric constant. The poling dynamics involving urea dipoles and ionic species was discussed. (C) 1996 American Institute of Physics.