Ferroelectric properties of NaNbO_3-BaTiO_3 thin films deposited on SrRuO_3/(001)SrTiO_3 substrate by pulsed laser deposition

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(NaNbO_3)_<1-x>(BaTiO_3)_x (NN-xBT) thin films with low BaTiO_3 (BT) concentrations x (x=0.05 and 0.10) were fabricated on SrRuO_3/(001)SrTiO_3 (SRO/(001)STO) substrate by pulsed laser deposition (PLD). X-ray diffraction pattern (XRD) and transmission electron diffraction pattern (TED) showed that NN-0.10BT thin film was epitaxially grown on SRO/(001)STO substrate with a crystallographic relationship of [001]_<NN-xBT>‖[001]_<STO>. From reciprocal space maps, the lattice parameters of the out-of-plane direction of NN-xBT thin films became larger with an increase in BT concentration, although the lattice parameter of the in-plane was hardly changed by the BT concentration. The value of relative dielectric constant ε_r of the NN-xBT thin films were increased with BT concentration. The ε_r and the dielectric loss tanδ of NN-0.10BT were 1220 and 0.02 at 1kHz, respectively. The P-E hysteresis loops of the NN-xBT thin films showed clear ferroelectricity. Although the value of remanent polarization P_r decreased with the BT concentration, the behaviors of ε_r, P_r, and coercive electric field E_c of the NN-xBT thin films against the BT concentration accorded with those of NN-xBT ceramics, in which NN-0.10BT ceramics exhibited the largest piezoelectric property. Therefore, the NN-0.10BT thin film is expected to show high piezoelectricity.
2009-01-01