Structure and properties of Pb(LuNb)O₃-PbTiO₃ ceramics and thin films

The crystallographic features of binary system Pb(LuNb)O 3 -PbTiO 3 (PLuNT) including the morphotropic phase boundary (MPB) region between tetragonal P4mm and pseudo-monoclinic M phases are reported and discussed with respect to dielectric, polarization and electromechanical characteristics. Non-isovalent doping of PLuNT in the Pb sublattice according to 2Pb 2+ → 2La 3+ + □ A either in both components or maintaining the PbTiO 3 unmodified: (i) shifts the MPB to the pseudo-monoclinic side of the phase diagram; (ii) diminishes the distortion of the unit cell (c/a - 1 = 0.009 at 2 mol.% of La); (iii) reduces the coercive field to 15.8 kV/cm in the first case and below 10 kV/cm in the latter case. Simultaneously high values of maximum polarization P m = 50.3 μ C/cm 2 and remnant polarization Pr ≅ 40.3 μ C/cm 2 maintain. The films of PLuNT with composition near the MPB formed by in situ pulsed laser deposition (PLD) onto LSCO/(100)MgO exhibited ferroelectric (FE) behaviour with P m ≅ 29 μ C/cm 2 , P r ≅ 14 μ C/cm 2 , E c ≅ 70 kV/cm. The zero-field dielectric permittivity ε = 300-450 at room temperature, and demonstrates a relaxor type broad peak around 350C. Au/PLuN/LSCO thin film heterostructures exhibit FE behaviour as well in contrast to typical AFE features of PLuN ceramic; a diffuse peak of ε was observed around 100C. The lower degree of structural ordering is considered to be the main factor in the different behaviour of thin films and bulk ceramic material.