ABSTRACTIn situ X-ray diffraction is one of the most useful tools for studying a variety of processes, among which crystallization of nanoparticles where phase purity and size control are desired. Growth kinetics of a single phase can be completely resolved by proper analysis of the diffraction peaks as a function of time. The peak width provides a parameter for monitoring the time evolution of the particle size distribution (PSD), while the peak area (integrated intensity) is directly related to the whole diffracting volume of crystallized material in the sample. However, to precisely describe the growth kinetics in terms of nucleation and coarsening, the correlation between PSD parameters and diffraction peak widths has to be established in each particular study. Corrections in integrated intensity values for physical phenomena such as variation in atomic thermal vibrations and dynamical diffraction effects have also to be considered in certain cases. In this work, a general correlation between PSD median value and diffraction peak width is deduced, and a systematic procedure to resolve time-dependent lognormal PSDs from in situ XRD experiments is described in details. A procedure to correct the integrated intensities for dynamical diffraction effects is proposed. As a practical demonstration, this analytical procedure has been applied to the single-phase crystallization process of bismuth ferrite nanoparticles.

Engineering of thermoelectric materials requires an understanding of thermal conduction by lattice and electronic degrees of freedom. Filled skutterudites denote a large family of materials suitable for thermoelectric applications where reduced lattice thermal conduction attributed to localized lowfrequency vibrations (rattling) of filler cations inside large cages of the structure. In this work, a multiwavelength method of exploiting X-ray dynamical diffraction in single crystals of CeFe 4 P 12 is presented and applied to resolve the atomic amplitudes of vibrations. The results suggest that the vibrational dynamics of the whole filler-cage system is the actual active mechanism behind the optimization of thermoelectric properties.

In situ synchrotron X-ray powder diffraction is used to elucidate the formation mechanism of multiferroic BiFeO3 nanoparticles during moderate heat treatment at ambient pressure of an amorphous precursor. A wet chemical synthesis is used to obtain the precursor, formed after solvent elimination of an aqueous solution containing iron and bismuth nitrates and tartaric acid. The in situ experiments are performed at two reaction temperatures and two heating rates, both giving rise to the growth of BiFeO3 nanoparticles without going through any intermediate crystalline phases. A detailed XRD line profile intensity analysis as a function of time and temperature provides information on the nucleation rate, growth kinetics, and size distribution of the nanoparticles.

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