Deposition of Pb(Zr,Ti)O 3 -Thin Films on Substrates with Shape Memory Effect
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ABSTRACT Pulsed Laser Deposition (PLD) was used to deposit La-doped Pb(Zr,Ti)0 3 (PZT) thin films onto NiTi foils. The substrate alloy with composition Ni50Ti50 shows a strong shape memory effect with a transition temperature of about 80 'C. This simple bicomponental system could have the potential of an actuator device (NiTi shows a strain up to 5 % during thermal cycling) with an inherent sensorial component (PZT) for the generated elongation. The deposited ceramic films were characterized with respect to their structural properties (XRD) and their ferroelectric behavior (P-E hysteresis). Under certain deposition conditions the growth of pure perovskite PZT on the polycrystalline shape memory alloy was observed. The growth morphology of PZT on NiTi was compared to the one of PZT on single crystalline substrates whereas no distinctive texture of the films on NiTi could be found. The ferroelectric behavior of the PZT films depend on the stage of bending of the film-substrate compound.
INTRODUCTION The aim of the present paper is to study the combination of NiTi as an actuation material covered with PZT as a sensing material. The promising sensorial potential of PZT in thin film microtechnology has been investigated and discussed by several groups [1, 2]. On the other hand, NiTi is used in a lot of technical applications where a temperature controlled movement without any electrical supply is desired [3]. The direct deposition of ferroelectric ceramics on any conducting material actually leads to a straightforward simple system, consisting of only two components, e.g. PZT // stainless steel Hastelloy [4]. There is no need for additional buffer layers or bottom electrodes, simplifying the system for applications. The present study focuses on the phase formation (ferroelectric perovskite phase, secondary nonferroelectric phases) and texture of the deposited films on the NiTi substrates. Furthermore, the morphology of the films on the polycrystalline NiTi sheet was investigated and compared with single crystalline substrates.
EXPERIMENT The PZT thin films were prepared by pulsed laser deposition (PLD). The light of a KrF Excimer laser 0. = 248 nm, E = 700 mJ/pulse, repetition rate = 16 Hz) was focused on a rotating cylindrical target (1JS Ljubljana) to ablate La-doped PZT ((Pbo 92Laoo0)(ZrossTi0 35)O 3). The NiTisubstrates (56 ýtm-thick foils of 10 x 10 mm 2, Memory-Metalle GmbH) were heated conventionally by a resistive heater. The deposition temperature was varied between 600'C and 670 °C at oxygen pressures of 0.1 mbar. The phase formation and the morphology of the deposited films were investigated by XRD (Cu-IK11 , 0-20 scans and pole figures) and SEM, respectively. Silverpaste top-electrodes were applied ex-situ for measuring the ferroelectric hysteresis of the deposited films with a modified Sawyer-Tower circuit (Radiant Technologies, RT-66A). 493 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
RESULTS Phase.formation At first, the influence of a heating procedure under deposition condit
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