Dynamic Monte Carlo simulation of spin-lattice relaxation of quadrupolar nuclei in solids. Oxygen-17 in yttria-doped ceria

Abstract

Although measurement of spin-lattice relation time (T1) can provide valuable information about atomic motion in solids, T1 data for quadrupolar nuclei are often difficult to interpret because the relevant physical interactions cannot be expressed analytically. In order to address this problem, we have developed an extension to the dynamic Monte Carlo method for simulating spin-lattice relaxation of quadrupolar nuclei in solids. In this paper we develop the simulation method generally, and then apply the method to understanding published T1 measurements of oxygen-17 in yttria-doped ceria. We show that even for simple geometries of motion, multiple time scales for electric field gradient fluctuations are possible, resulting in complex relaxation behavior including multiple T1 minima. The method can be used to explain and deconvolute data in which these effects are present. In the case of yttria-doped ceria, we show that two experimentally observed T1 minima result from simultaneous movement of oxygen vacancies and oxygen ions. We discuss the meaning of the kinetic parameters extracted from the data, and show evidence for the relevance of these parameters to bulk vacancy diffusion kinetics.