Hard mode infrared spectroscopy of CaTiO3-CaFeO2.5 perovskites

Powder-absorption infrared (IR) spectra of perovskites CaFexTi1-xO3-x/2 (0 less than or equal to x less than or equal to 1) annealed at different temp eratures were investigated at room temperature in the range 135-2000 cm(-1) . The spectra change as a function of composition, annealing temperature an d structural state (order-disorder of oxygen vacancies). Autocorrelation an alysis has been used to determine variations of average line widths of grou ps of peaks in the primary IR spectra. The band widths increase on increasi ng Fe content in the region of the structures with disordered oxygen vacanc ies and they decrease on going through the order-disorder boundary. High de grees of local structural heterogeneity are suggested by the effective line widths of the phases at intermediate compositions. The intensity of bands at similar to 150 and similar to 443 cm(-1) decreases with increasing Fe co ntent in the compositional range of the disordered structures. Finally, for every annealing temperature, the frequency of the band at similar to 600 c m(-1) systematically shifts to higher values on increasing Fe content, thes e values decreasing again for the fully ordered structures.