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Raman spectra of anhydrous crystalline samples of all of the lanthanide orthophosphates (with the exception of PmP04) have been obtained. These data were interpreted in a systematic manner based on the known structures of these compounds. Assignments and correlations have been made for many of the observed bands.

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March 1987Thus, on gradual addition of silica sol to A13' sol during gelation and the subsequent heating, Si-A1 spinel will form with association of amorphous aluminosilicate phase. The composition and amount of the amorphous phase will be expected to change with such additions. As a result, the observed 0.139-nm peak area (Table 11) is found to decrease with increasing percent of SiOz instead of remaining more or less constant and equal to the area of the standard y-Alz03. Therefore, any attempt to prepare pure Si-A1 spinel would be a mixture of Si-A1 spinel and an amorphous ahminosilicate phase. As a result, the XRD intensity would be less than that of pure y-A1203.The sodium titanates Na4Ti04, a-, /3, and y-NaJi03, Na8Ti50,,, Na2Ti307, and NazTi60,s, all of which can be synthesized in the temperature range 800" to 12OO0C, have been characterized by X-ray diffraction (XRD) and Raman spectroscopy. The existing XRD data have been critically reviewed and several inconsistencies and errors have been identified.