Effect of Cu dopant on microstructure and phase transformation of ZnTiO3 thin films prepared by radio frequency magnetron sputtering
Introduction
As the need for versatile electronic components with high reliability increase, the development of high-frequency electronic materials becomes imperative. Zinc titanate (ZnTiO3) has been reported to have specific electrical properties that are adequate for applications in microwave dielectrics [1]. The ZnO–TiO2 system exists in three forms: zinc meta-titanate (ZnTiO3) with a hexagonal ilmenite structure; zinc ortho-titanate (Zn2TiO4) with a cubic spinel crystal structure; and zinc polytitanate (Zn2Ti3O8) with a cubic defect spinel structure [2]. Steinike et al. [3] has reported Zn2Ti3O8 materials which was a low-temperature form of ZnTiO3, and it exists at temperature < 820 °C. The Zn2Ti3O8 compound was formed based on the Zn2TiO4 phase [4]. However, hexagonal ZnTiO3 decomposes into cubic Zn2TiO4 and rutile TiO2 at T > 945 °C [5]. Moreover, ZnTiO3 single-phase compound can be prepared by zinc oxide and rutile hydrate at T = 850–900 °C [2].
Pure ZnTiO3 shows good dielectric properties in the microwave range. It has a perovskite-type oxide structure, which could be advantageous as a microwave resonator material [6]. Furthermore, ZnTiO3 can be sintered at 1100 °C without the use of sintering aids [5], [6]. Moreover, when a sintering aid is added, it can be fired at temperatures below 900 °C [7], [8]. ZnTiO3 has potential applications in gas sensors that detect ethanol or carbon monoxide. It is also a promising candidate for the use in nonlinear optics, as a luminescent material and in various photocatalytic roles [9], [10].
Pure zinc titanate thin films have been prepared by radio frequency (RF) magnetron sputtering in previous studies [11]. It was shown that crystallization of the ZnTiO3 phase occurred at a substrate temperature of 400 °C and annealing temperature of 700 °C over 2 h. However, as the annealing temperature exceeded 900 °C, the ilmenite ZnTiO3 decomposed into cubic Zn2TiO4 and rutile TiO2. In the present work, Cu doped zinc titanate thin films were prepared by RF magnetron sputtering. The microstructure and phase transformation of zinc titanate thin films with different Cu contents were subsequently investigated.
Section snippets
Experimental procedure
The Cu doped zinc titanate thin films were prepared by RF magnetron sputtering, the deposition conditions were listed as below.
A bulk zinc titanate target was synthesized by conventional solid-state methods from high-purity oxide powders; ZnO and TiO2 (> 99.9%). The starting materials were mixed according to the stoichiometry of ZnTiO3. The powder was then sintered and pressed into disks with a diameter of 3 in. and thickness of 3 mm. These were subsequently used as ZnTiO3 targets. To dope the
The effect of Cu dopants on the microstructure and phase transformation of zinc titanate thin films
Fig. 2 shows the X-ray diffraction (XRD) patterns of the 0.84 at.% Cu doped zinc titanate thin films annealed at 600, 700, 800 and 900 °C. It was observed that the as-deposited thin films were amorphous, indicating that no crystallization occurred in the as-deposited thin films. At 600 °C, some peaks appeared, and the intensity increased rapidly up to 700 °C. At 600 °C, the majority crystalline phases was identified as cubic (Zn,Cu)2Ti3O8, which is a low-temperature form of ZnO–TiO2 system, as
Conclusion
Zinc titanate thin film with Cu dopant was fabricated by a radio frequency magnetron sputtering. The effects of Cu dopant and content on the microstructure and phase transformation of zinc titanate thin films have been investigated, and the results were summarized: (1) For 0.84 at.% Cu doping, it is found that the as-deposited films were amorphous, as confirmed by the XRD results. As-deposited amorphous film began to be crystallized into (Zn,Cu)2Ti3O8, (Zn,Cu) TiO3, and TiO2 phases at the
Acknowledgment
The authors would like to acknowledge the financial support of this research by the National Science Council of Taiwan under contract No. NSC-98-2221-E-020-003.
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