Structure and ferroelectric properties of single crystal PMNT thin films

Single crystal thin films of relaxor PMNT, (1-x)PbMg1/3Nb2/3O3-xPbTiO(3), x = 0 to 0.35, were hetero-epitaxially grown on (001) SrTiO3 by a magnetron sputtering. XRD study showed the unit cell of the PMNT thin films was a c-enlongated tetragonal with highly strained structure at the film thickness below 50 nm. As the film thickness increased above a critical film thickness of around 300 nm, the PMNT thin films evolved from the tetragonal phase to the pseudo-cubic of relaxed structure. We have evaluated the dielectric properties of the relaxed single crystal PMNT thin films. The dielectric constant increased with the increase of the PT as expected: The room temperature dielectric constants at 100 kHz were 800 for PMN and 2700 for PMN-35PT. The PMN-35PT thin films, however, showed a broad temperature anomaly with low maximum dielectric constants of 4800. The d(33) piezoelectric coefficients estimated were 290 pC/N which were different from bulk single crystal values by half order of magnitude, although the dielectric and piezoelectric properties of the relaxed structure were expected to be compatible to bulk materials. The low dielectric constant was not simply attributed to the stress and/or interfacial effect.