Compositional homogeneity of ferroelectric (Pb,La)(Ti,Zr)O 3 thick films
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R.B. Marinenko National Institute of Standards and Technology, Gaithersburg, Maryland
J. Holc, Z. Samardžija, M. Cˇeh, and M. Kosec Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia (Received 25 August 2002; accepted 21 November 2002)
Quantified wavelength dispersive spectroscopy (WDS) x-ray element maps were used to characterize active (Pb,La)(Ti,Zr)O3 (PLZT) layers on Pt/PLZT/Al2O3 substrates, one fired at 1050 °C and the other at 1150 °C. In the layer fired at 1050 °C, randomly distributed micrometer-sized compositional irregularities were observed as La-rich regions that were in most cases enriched also with Ti and deficient in Pb and Zr compared to the matrix. Such compositional imperfections were not observed in the PLZT layer fired for the same duration at 1150 °C. The level of microheterogeneity for all elements in the specimen fired at 1150 °C and for Pb, Ti, and Zr in the specimen fired at 1050 °C was below 1% relative at confidence level of 99% while for La it was as much as 2.5% relative. In point-beam line profiles across the active layer starting from the Pt electrode toward the outer surface of the cross-section of the PLZT film, the Pb concentration decreased continuously in both samples, confirming the importance of providing a properly equilibrated partial pressure of Pb around the sample during the entire firing process. Better dielectric and ferroelectric characteristics of the specimen fired at 1150 °C compared to the sample fired at 1050 °C were attributed to the differences in compositional heterogeneity between these samples. The study of the micro-compositional characteristics of these ceramic materials with quantitative WDS mapping has contributed to the optimization of processing parameters and hence to the understanding of the properties of ferroelectric PLZT materials.
I. INTRODUCTION
There is a continuing interest in the development of ferroelectric ceramic materials based on solid solutions of Pb(Zr,Ti)O3 (PZT) and La-doped (Pb,La)(Ti,Zr)O3 (PLZT) because of the numerous applications of these materials in the electronics industry. Attention so far has been concentrated on the development and characterization of ferroelectric thin films, with typical thicknesses from 10 to 1000 nm, deposited on a substrate by various techniques such as sputtering, evaporation, and the chemical solution deposition technique. Much less attention has been paid to the processing of thicker ferroelectric films with thickness of a few micrometers up to tens of micrometers. There are possible uses of ferroelectric thick films in pyroelectric sensors, gravimetric sensors, micropumps, pressure sensors, and surface acoustic wave devices.1–6 The memory effect of rhombohedral PLZT makes this ferroelectric ceramic material a prime J. Mater. Res., Vol. 18, No. 2, Feb 2003
candidate for high-speed electrophoretic printing,7 exploiting its rectangular hysteresis loop, high remnant polarization (Pr), and low coercive field (Ec). This application also requires a highly dense structure with negligible defe
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