Pulsed laser deposition was used to grow thin films of several compositions from the Pb(Mg1/3,Nb2/3)O3–PbTiO3 (PMN–PT) solid solution as dielectric layers in thin film capacitor structures. They were found to display functional behavior characteristic of relaxors, with the only significant difference between thin film and bulk being a severely reduced dielectric permittivity. Room temperature polarization loops showed a general increase in both the remanent polarization and absolute magnitude of the polarization for a given field with PT content. The electric field-induced strain was primarily examined by in situ x-ray diffraction and although fields greater than 20 MV m−1 were applied to the films, the maximum observed strain was only ∼0.3%, considerably less than the 1.4% seen in single crystal samples. Piezo-response atomic force microscopy studies were consistent in that the macroscopic effective piezoelectric coefficient d33, was found to differ from single crystal measurements by an order of magnitude. However, electrostrictive coefficients (Q33), were found to be comparable to published values for both PMN–PT single crystals and ceramics, ranging between 1 and 9×10−2 C−4 cm2. Consequently, it seems that the relatively poor strain response in these thin films is intimately linked to the reduced permittivity and not to a fundamental difference in the electrostrictive coefficients between bulk and thin film.
Thin film capacitors of Au/Pb(Mg1/3Nb2/3)O3–7%PbTiO3 [PMN–(0.07)PT]/(La1/2Sr1/2)CoO3 were made by pulsed laser deposition on single crystal {001} MgO substrates. The PMN–(0.07)PT dielectric was perovskite dominated, and demonstrated functional behavior typical of relaxors. Electrostrictive behavior was observed at fields up to 200 kV cm−1, however, the maximum strain was disappointingly low at only ∼0.14%. The macroscopic electromechanical d33 and Q33 coefficients were determined using piezo-response atomic force microscopy. At 100 kV cm−1 the macroscopic Q33 was found to be (2.6±0.2)×10−2 C−2 m4. The crystallographic electrostrictive coefficient was determined using in-situ x-ray diffraction and at the same field found to be significantly higher: (4.9±0.2)×10−2 C−2 m4. Since these electrostrictive coefficients are of the same order of magnitude as found in single crystal experiments (2.5–3.8×10−2 C−2 m4), it appears that the low out-of-plane strain is simply the result of poor polarizability in the thin films. An effective Q13 component of the electrostrictive tensor was also determined, and found to be ∼−0.32 ×10−2 C−2 m4.
Thin film capacitor structures of Pb(Mg1/3Nb2/3)O3 (PMN) - PbTiO3 (PT) were fabricated using pulsed laser deposition (PLD) on MgO{100} substrates using (La1/2,Sr1/2)CoO3 (LSCO) as a lower electrode. Crystallographic and dielectric characterisation confirmed perovskite relaxor-like behaviour. Measurements of the electrostrictive coefficients by in-situ X-ray diffraction, piezo-response atomic force microscopy and three point bending experiments showed both Q11 and Q13 to be comparable to accepted values for single crystals. However, for a given field, the electric field-induced strain in the thin films was much less than that of single crystal. This was clearly intimately linked to poor thin film polarisability. Previous work had shown sol-gel PMN-PT films to have significantly greater permittivities than PLD films, and a TEM investigation was undertaken to see if functional differences could be related to differences in microstructure, and hence if the functional and electromechanical properties of PLD films could be improved by attempting to replicate sol-gel microstructures.
Pulsed laser deposition (PLD) was used to growth thin films of lead zirconium titanate (PZT) and lead zinc niobate-barium titanate (PZN-BT). The PZT films were prepared from commercial PZT-5H ceramic target and the PZN-BT made from target made using a modified Columbite method. The PZT films had dielectric constants of 300 and loss of 0.03 at 10kHz, whilst for the PZN-BT films they were 350 and 0.03 respectively at 300K. Hysteresis measurements confirmed their switching propertiesA piezoresponse microscope based on a modified atomic force microscope was developed to determine electromechanical response at a sub-micrometer resolution. The PZT films yielded d33 ∼100pm/V. Mapping measurements on the PZT demonstrated local switching of individual grains. First measurements of piezoresponse of PZN-BT yielded values in the region 150-200 pm/V.
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