Structure and transmittance of Cr³⁺ doped MgO?nAl₂O₃ (0.9n1.2) ceramics

Transparent spinel ceramics (MgO center dot nAl(2)O(3), n = 0.9-1.2) doped with Cr3+ ions were prepared by hot-pressed sintering in a vacuum. The effect of the composition on the microstructure, densification, and transmittance of ceramics was studied. The single phase of spinel was obtained at n >= 0.95, and their relative density changed insignificantly and was about 99%. As the n value increased, the Al3+ ions were preferred to locate the tetrahedral sites in the spinel structure. At n = 1, approximately 65% of Al3+ ions occupied the T-sites, and at n = 1.2, it increased to 77%. The occupation of Cr3+ ions was not affected by the Al3+ occupation, and the ratio of Cr3+ ions in T-sites to O-sites was still about 1:1, regardless of the value of n. The transmittance of the ceramics was relatively high at 1 <= n <= 1.1, and the transmittance in the region of 1000-6000 nm was about 74-78%.