Electromechanical properties and self-polarization in relaxor Pb(Mg1/3Nb2/3)O-3 thin films

Pyrochlore free Pb(Mg1/3Nb2/3)O-3 (PMN) thin films were prepared from alkox ide-based solution precursors. The influence of different seeding layers an d chemical solution on the microstructures is shown. Dielectric, electrostr ictive, and piezoelectric properties of the films were characterized in det ail. Films show relaxor-like behavior, but with dielectric permittivity whi ch is low (around 4000 at peak) compared to bulk ceramics and single crysta ls. Several parameters which might be responsible for this lower permittivi ty are suggested. Electrostrictive coefficients, M and Q, were determined b y measuring strain S and polarization P as a function of the electric field (E-ac). At large fields (>2.6x10(6) V/m), S vs P-2 appears to deviate from linear behavior possibly suggesting that the electrostrictive coefficient Q becomes nonlinear in this field range. Investigated as-prepared PMN films exhibit piezoelectric response in the absence of a dc electric field (d(33 )=8-20 pm/V). The value of the associated self-polarization in the films is estimated and its presence confirmed by zero-field pyroelectric measuremen ts. The self-polarization and the piezoelectric coefficient are strong func tions of the ac field amplitude. Asymmetry of S vs E-ac and d(33) vs E-dc l oops are related to the self-polarization. An ac field induces shift in P v s E loops along the field axis. This increase in the coercive field is asso ciated, through a simple model, with the presence of the self-polarization. (C) 2001 American Institute of Physics.