Raman and Mossbauer Spectroscopy and X-ray Diffractometry Studies on Quenched Copper-Ferri-Aluminates

Four spinel ferrite compositions of the CuAlxFe2-xO4, x = 0.0, 0.2, 0.4, 0.6, system prepared by usual double-sintering ceramic route and quenched (rapid thermal cooling) from final sintering temperature (1373 K) to liquid nitrogen temperature (80 K) were investigated by employing X-ray powder diffractometry, Fe-57 Mossbauer spectroscopy, and micro-Raman spectroscopy at 300 K. The Raman spectra collected in the wavenumber range of 100-1000 cm(-1) were analyzed in a systematic manner and showed five predicted modes for the spinel structure and splitting of A(1g) Raman mode into two/three energy values, attributed to peaks belonging to each ion (Cu2+, Fe3+, and Al-3+()) in the tetrahedral positions. The suppression of lower-frequency peaks was explained on the basis of weakening in magnetic coupling and reduction in ferrimagnetic behavior as well as increase in stress induced by square bond formation on Al3+ substitution. The enhancement in intensity, random variation of line width, and blue shift for highest frequency peak corresponding to A(1g) mode were observed. The ferric ion (Fe3+) concentration for different compositions determined from Raman spectral analysis agrees well with that deduced by means of X-ray diffraction line-intensity calculations and Mossbauer spectral analysis. An attempt was made to determine elastic and thermodynamic properties from Raman spectral analysis and elastic constants from cation distribution.