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Rare earth (RE) halides (fluorides, chlorides, bromides, and iodides) have been studied by X-ray photoelectron spectroscopy. The binding energies (BE’s) of the RE 3d and 4d peaks for the chlorides, bromides, and iodides are related to the atomic charge calculated on the basis of Pauling’s scale of electronegativity (Pauling charge). Except for Y and Lu, the observed RE 3d and 4d BE’s for the fluorides are lower than those expected. For Y and Lu, the observed RE 3d and 4d BE’s for all halides are related to the Pauling charge. For the fluorides and chlorides, the BE’s of the ligand peak show variations with increasing atomic number of RE’s and a specific “tetrad effect” is observed in plots of BE versus RE atomic number and versus 1/R (where R is the mean distance from the ligand atom to the neighboring RE atom), except for the BE’s of the F 1s peaks from the light RE fluorides. For the iodides and bromides, no or little characteristic variations are seen in the BE’s of I and Br.

An application of diffuse reflectance infrared Fourier transform (DRIFT) spectrometry to determine powdery sample with an unknown particle size has been proposed. The usefulness of this technique has been demonstrated for the analysis of the α-component in Si3N4 powders. The particle size of the α-component in Si3N4 powder could be determined by measuring the peak intensity ratio between two peaks (500 and 690 cm−1) on the DRIFT spectrum, and the concentration could be determined by comparing the peak intensity to that of standard α-Si3N4 with same particle size. The particle sizes and concentrations obtained by the DRIFT method were in good agreement with those obtained by the light-scattering method and x-ray diffractometry, respectively.

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