Pyroelectric or piezoelectric compensated ferroelectric composites

The matrix and inclusions of 0-3 composites of lead titanate (PT) in polyvinylidenefluoride trifluoroethylene (P(VDF-TrFE)) have been independently poled by a special poling method. The polarization states of both constituents are investigated by the measurement of the dynamic pyroelectric coefficients of the composites in the temperature range of 20-90 degrees C, within which the copolymer matrix undergoes a ferroelectric-paraelectric phase change. The pyroelectric coefficients of PT and P(VDF-TrFE) have the same sign, while their piezoelectric coefficients have opposite signs. This allows the preparation of composites with enhanced pyroelectric but reduced piezoelectric activity when the matrix and inclusions are polarized in the same direction, or vice versa if the constituents are oppositely polarized. For a PT volume fraction of 27% it was possible to prepare a pyroelectric composite with vanishing piezoelectric activity or a piezoelectric composite with vanishing pyroelectric activity by poling the matrix and inclusions in parallel or antiparallel directions. (C) 2000 American Institute of Physics. [S0003-6951(00)04719-7].