Dielectric and microstructural properties of barium titanate zirconate thin films on copper substrates
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W. Borland DuPont Electronic Technologies, Research Triangle Park, North Carolina 27709 (Received 19 April 2005; accepted 14 July 2005)
Barium titanate zirconate, Ba(Ti1−xZrx)O3 (0 艋 x 艋 0.25), thin films were deposited via the chemical solution deposition (CSD) method directly on copper foils. The films were processed in a reductive atmosphere containing nitrogen, water vapor, and hydrogen gas at 900 °C to preserve the metallic copper substrate during crystallization. Increasing the fraction of BaZrO3 revealed several effects, including an increase in unit cell dimensions, a decrease in both the temperature and value of the maximum permittivity, as well as a decrease in the average grain size of the films. The decrease in the relative permittivity was attributed to a grain size effect as opposed to zirconium substitution. In film compositions containing 25 mol% BaZrO3, the permittivity below Tmax became dispersive, and the ferroelectric transitions became increasingly diffuse. These characteristics suggest relaxor-like behavior. The dielectric tunability of Ba(Ti1−xZrx)O3 was studied at room temperature and at Tmax for each composition. There was little variation in the tunability with measurement temperature; however compositions that were ferroelectric at room temperature saw a decrease in hysteresis at Tmax, and all compositions showed an increase in permittivity.
I. INTRODUCTION
Barium titanate zirconate (BTZ) is a well-known ferroelectric material that has garnered attention for applications in which its tunable dielectric constant or high permittivity can be exploited.1–3 The addition of barium zirconate (BZ) to barium titanate (BT) allows for a variety of interesting phenomena to occur. Much like strontium titanate, barium zirconate has been used to shift the Curie point to lower temperatures to allow for the maximum in permittivity to occur in a temperature regime more favorable for room-temperature applications. In contrast to the alloying of barium titanate with strontium titanate, however, the addition of zirconium shifts the lower temperature transitions to higher temperatures resulting in a Curie temperature pinching effect.4,5 This pinching effect increases and broadens the overall peak in permittivity and lowers the temperature coefficient of capacitance. The temperature response of BTZ has also been investigated and the relaxor ferroelectric characteristics of a diffuse phase transition, dispersion in the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0342 2838
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 10, Oct 2005 Downloaded: 07 Feb 2015
permittivity,6,7 and a Tmax shift with an applied direct current (dc) field have been reported.8 It is accepted that in bulk ceramics, a composition containing 26 mol% zirconium shows relaxor behavior while those with less zirconium display a diffuse phase transition with no frequency dispersion.9 Several groups have investigated the dielectric and relaxor properties of this material in
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