Structural, electrical and catalytic properties of ion-implanted oxides

Abstract

Abstract. The potential application of ion implantation to modify the surfaces of ceramic materials is discussed. Changes in the chemical composition and microstructure result in important variations of the electrical and catalytic properties of oxides. 66.30, 81.40, 81.60, 61.70 Since the introduction of ion implantation as a surface modification technique, the electrical [1, 2], optical [3], magnetic [4], chemical [5], mechanical [6] and topographical [7] properties of solids have been modified. The potential use of ion implantation to modify the surfaces of ceramic materials has been discussed by Burggraaf et al. [56]. These changes in the macroscopic properties correspond to the changes in chemical composition and microstructure. In this paper this relationship is discussed for the electrical and catalytic properties of oxides, modified by ion implantation. PACS: Ion ImplantationIn the ion-implantation process, specific atoms are ionized, accelerated and mass selected [8]. Those high energetic ions (15 keV-2 MeV) penetrate in the solid and come to rest due to elastic and inelastic energy loss processes. A comprehensive treatment of the penetration of ions in solids has been given in [-9 and 10]. Depending on the process parameters the depth profile can be given different shapes, the penetration depth can be varied between some nanometers and about one micrometer and the dopant concentration in the surface can be raised to about 50 at.%. When the ion beam is properly scanned over the surface, lateral very uniform concentrations of the dopant are obtained. Due to the electrical control of the ion energy and dose, the technique is very reproducible.A major advantage of ion implantation is that a surface layer can be doped with any element, independent of its solubility in the substrate material. This means that one can produce metastable compounds, strongly supersaturated solid solutions and complex microstructures consisting of very finely dispersed precipitates with nanoscale dimensions in a matrix material. Several examples are discussed below. Microstructural Changes As-Implanted StateWhen an ion is implanted, it collides with the nuclei and electrons of the solid. In ionic oxides, only nuclear collisions result in defects [11]. Vacancies and interstitials are generated in both the anion and the cation sublattice. Interstitial loops nucleate and grow during irradiation. The lattice damage initially increases with the dose and finally saturates [11]. At that point as many defects are generated as annihilated by dynamic recovery processes in the solid. Dynamic recovery processes can be suppressed by cooling the target to low temperatures.The accumulation of defects in ion-implanted solids can result in a transition from a crystalline to an amorphous phase. This has been observed for, e.g., A1203 [12,13] [25]. The main conclusion from this model is that Fe 3 + can only exist in MgO as an isolated impurity. The fraction of Fe z + and Fe ~ is determined by the probability that, respectively, two Fe atoms and ...

Microstructure and thermal stability of Fe, Ti, and Ag implanted yttria-stabilized zirconia

“…As previously reported, the recrystallisation of an amorphous layer depends strongly on the implanted ion [9]. An important step in the recrystallisation process is the nucleation of a crystalline phase.…”

“…This result implies that the grain size in the surface of a ceramic material can be decreased by ion beam amorphisation and subsequent recrystallisation at elevated temperatures. The major objective of the present study is to check the possibility to obtain by ion implantation a mixed conducting surface layer in YSZ [5][6][7][8][9] and in this way to investigate the possibility to increase the rate of electrochemical reactions at the gas-solid interface, Fe and Ti have been chosen as dopants since the corresponding oxides are semiconductors at the operating temperature of YSZ [10,11]. Some studies on the electronic properties of YSZ doped with transition metal oxides have shown that mixed conductivity is obtained.…”

Oxygen transfer properties of ion-implanted yttria-stabilized zirconia

“…[ 1 ], and the influence of implantation on their electrical and catalytic properties in ref. [2]. A disadvantage of ion implantation is that it is not well suited for large scale applications, e.g., implantation of large surface areas in the production of SOFC stacks.…”

Electronic properties of ion-implanted yttria-stabilized zirconia

“…Another solution is the modification of the solid electrolyte surface itself. Recent experiments have shown, that ion implantation in particular is a powerful technique to modify the surfaces of ceramic electrolytes [8][9][10][11]. Four-point probe conductivity measurements on Ti-implanted yttria-stabilized zirconia thin films (53 nm thick), showed an increase of the total conductivity by a factor 100-1000 after reduction in H2 (PH2 = 1 atm, 800°C) [ 12].…”