SYNTHESIS AND CHARACTERIZATION IN THE NEW SYSTEM BI_2(AL/GA)_4O_49 AND ~(18)O/~(16)O EXCHANGE EXPERIMENTS

摘要

Compositions in the new system Bi_2(Ga_xAl_(1-x))_O_9 (x = 0, 0.1, ....,1) having mullite-type structure were synthesized using precursor gels obtained from the solution of corresponding nitrates in glycerin. The effects of Ga/Al substitution were characterized by IR absorption spectroscopy and X-ray powder diffraction (XRD). The linear change in lattice parameters related on x indicate ideal solid solution behaviour. The splitting of the high frequency vibration mode in the mixed composition indicate the presence of Ga-O_c-Ga, Ga-O_c-Al and A1-O_c-A1 bonds, where O_c is the common oxygen of the double tetrahedral unit. ~(18)O/~(16)O isotope exchange experiments (at 800°C) show the extraordinary dominance of the Oc atom in this vibration. The relative absorption intensities of the M-~(18)O_c/~(16)O_c vibrations used to estimate diffusion coefficient showing value of about 4*10~(-15) cm~2/s and l.l*10~(18) cnr/s for Bi_2Ga_4O_9 and Bi_2Al_4O_9, respectively.