Temperature-dependent ferroelectric properties of (Pb 0.75 La 0.25 )TiO 3 thin films
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Polycrystalline (Pb0.75La0.25)TiO3 (PLT25) thin films have been fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. The room-temperature structures and dielectric properties are studied by x-ray diffraction, scanning electron microscopy, and HP4294A impedance/phase analyzer. The temperature-dependent ferroelectric properties are systematically investigated by using a RT66A ferroelectric tester combined with a temperature-controllable vacuum chamber. For well-saturated hysteresis loops, with the temperature decrease from 295 to 97 K, the coercive field (Ec) and remanent polarization (Pr) increase and the saturated polarization (Ps) is almost temperature-independent. However, this is not the case for the unsaturated hysteresis loops. Temperature-dependent fatigue-resistance of the PLT25 films is also experimentally established: after 2.22 × 109 switching cycles, the nonvolatile polarization decreases 38% when measured at room-temperature and it decreases 15% at 97 K. The nature and population of point defects and their effects on the subtle variations of the Ec, Ps, Pr, and fatigue-resistance against temperature are discussed in detail. I. INTRODUCTION
Ferroelectric thin films are important for various functional devices.1–3 Therefore, the ability to search for new ferroelectrics with special property is necessary. Recently, it was reported that by selective substitution, one can design the electrical property of ferroelectrics.4 For example, in the La-substituted PbTiO3 [(Pb1−xLax)TiO3 (PLTx)] material system, an appropriate control of the La composition allows for a wide range of optimized dielectric, piezoelectric, pyroelectric, nonlinear electro-optic, and ferroelectric properties, which enable the PLTx to be one of the promising material systems for use in various technological applications such as dynamic random access memory, micro-electro-mechanical system, and pyroelectric infrared sensors, and non-volatile ferroelectric random access memory (NVFRAM).5–10 In recent years, temperature-dependent structures and dielectric properties of PLTx thin films with different La composition have been studied.11–13 However, reports on their temperature-dependent ferroelectric properties are rare in the literature.14,15 Nevertheless, the temperature dependence of ferroelectric properties is one of the most important characteristics in view of not only engineering but also fundamental science.16 Therefore, it is interesting to systematically investigate the temperaturedependent ferroelectric properties of PLTx films. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0236 1638
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 6, Jun 2004 Downloaded: 15 Mar 2015
In this paper, Pb0.75La0.25TiO3 (PLT25) thin films were prepared on Pt/Ti/SiO2/Si substrates by pulsed laser deposition (PLD). The room temperature structures and dielectric properties were studied briefly while the temperature-dependent ferroelectric properties were investigated systematically. T
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