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Nanosize and superparamagnetism in Ce1-xGdxO2-x/2 samples investigated by PDF and EPR

Michela Brunelli 1Marco Scavini 2Cesare Oliva 2Serena Cappelli 2

1. Europen Synchrotron Radiation Facility (ESRF), 6, Jules Horowitz, Grenoble 38000, France
2. Università di Milano, Dipartimento di Chimica Fisica ed Elettrochimica, via Golgi, 19, Milano 20133, Italy



CeO2-based materials (Ce1-xMxO2-x/2; M = Gd, Y, Sm) have been intensively studied in the last years as catalysts, structural and electronic promoters for heterogeneous catalytic reactions and oxide ion conducting electrolytes for electrochemical cells. In particular, for use in electrochemical cells, Ce1-xGdxO2-x/2, solid electrolytes are characterised by an ion conductivity higher than conventional Yttria-Stabilized-Zirconia-based ones and would be able to operate at lower temperatures (500 - 700°C).

Thermodynamics transport and magnetic properties of nanostructured compounds can be quite different from that of bulk materials. In our recent works, the relation between the magnetic properties and the nanosize of Ce0.8Gd0.2O1.9 samples have been investigated. It will be shown that nanostructured Ce0.8Gd0.2O1.9 samples shows superparamagnetic behaviour. The extent of the inner field Ha is a function of the particle dimension (see Fig.1).

Figure 1: Left particle size distribution P(D) obtained throughout Warren-Averbach analysis for Ce0.8Gd0.2O1.9 nanocrystals; right internal field Ha as a function of particle diameter (DV) for the same composition.

The local structure of Ce1-xGdxO2-x/2 samples has been investigated by means of PDF analysis. In Fig. 2 the G(r) function of a microstructured Ce0.8Gd0.2O1.9 sample (black) is shown as well as the G(r) function relative to two nanostructured phases of the same compound. The G(r) amplitude of the nanostructured samples decreases rapidly at high r values due to the limited particle size.

Figure 2: G(r) function relative to Ce0.8Gd0.2O1.9 samples in the 1.5 < r < 10 Å and 90 < r < 100 Å regions. Black = microstructured; blue = sol-gel nanosample annealed at 700 °C; red = sol-gel nanosample annealed at 500 °C.

The local distortions introduced by Gd doping and nanosize structure of Ce1-xGdxO2-x/2 samples will be discussed.


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Submitted: 2008-04-29 17:50
Revised:   2009-06-07 00:48