Lanthanide series doping effects in lead zirconate titanate (PLnZT) thin films
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Paul G. Clem and Bruce A. Tuttle Sandia National Laboratories, Integrated Materials Research Laboratory, MS 1411, P.O. Box 5800, Albuquerque, New Mexico 87185
Geoffrey L. Brennecka University of Missouri—Rolla, Ceramic Engineering Department 222 McNutt Hall, 1870 Miner Circle, Rolla, Missouri 65409
Jeffrey T. Dawley and Mark A. Rodriguez Sandia National Laboratories, Integrated Materials Research Laboratory, MS 1411, P.O. Box 5800, Albuquerque, New Mexico 87185
Timothy D. Dunbarb) and William F. Hammetter Sandia National Laboratories, Advanced Materials Laboratory, MS 1349, 1001 University Boulevard, SE, Albuquerque, New Mexico 87105 (Received 23 August 2001; accepted 29 January 2002)
Lanthanide (Ln) doping of lead zirconate titanate (PLnZT 4/30/70) thin films was conducted to investigate effects on structural and electrical properties. Films were spin-coat deposited from precursor solutions made using a previously reported “basic route to PZT” chemistry. The remanent polarization (Pr), dielectric constant (⑀), dielectric loss (tan ␦), and lattice parameter values were obtained for each of the doped PLnZT films. Films doped with amphoteric cations (Tb, Dy, Y, and Ho) displayed high Pr values, square hysteresis loops, and enhanced fatigue resistance. Smaller radius Ln-doped films display an increased tendency toward (100) orientation in otherwise (111)-oriented films.
I. INTRODUCTION
Ferroelectric lead zirconium titanate (PZT) is used for a wide range of applications including nonvolatile memories,1 sensors,2 electro-optic devices,3 capacitors,4 and actuators.5 PZT is a perovskite ABO3 solid-state solution wherein the B-site composition can be continuously varied from the titanium-free PbZrO3 (PZ) at one extreme to pure PbTiO3 (PT) at the other. The ratio of Zr to Ti dramatically affects the properties of the PZT materials and is often represented numerically in an abbreviation, such as PZT (30/70), where the composite ratio is 30% Zr and 70% Ti. The inclusion of acceptor or donor dopants (i.e., the charge of the dopant being lower or higher than the metal cation for which it substitutes) is often used to alter the properties of PZT by suppressing or promoting oxygen or cation vacancies.6,7 While there a) b)
Address all correspondence to this author. Current address: 3M Company, Advanced Materials Technology Center, St. Paul, MN 55144. J. Mater. Res., Vol. 17, No. 4, Apr 2002
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have been substantial improvements in many of the properties of PZT using acceptor and donor dopants, it is important to garner greater understanding and control over the properties of ferroelectric materials. In particular, we are interested in understanding how dopants affect the remanent polarization (Pr), dielectric constant (⑀), dielectric loss (tan ␦), and fatigue characteristics of PZT thin films. Lanthanum doping of PZT (PLZT) is of particular interest for dielectric, piezoelectric, and electro-optic applications.3,6 La3+ was initially chosen as a dopant for the PZT system
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