Cation dopant effect on phase transformation and microstructural evolution in M2+-substituted γ-alumina powders

Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol–gel route under seeding

“…Among the divalent cation dopants reported in our previous study, Ca 2+ is by far the best dopant for suppressing the grain growth of -alumina upon heating [7]. The addition of -alumina seeds provides multiple low-energy sites for nucleation [8,12], which allows early impingement of the growing -alumina colonies, and hence, full densification at lower temperatures.…”

“…RE-doped samples obtained at 900°C without seeding consisted of -alumina with a trace of -alumina, but the -alumina tended to disappear with increasing RE content up to 0.50 mol%, as was the case for the M 2+ doping system [7]. In addition, the exothermic DTA peak temperature (Pm), which deduces the -to- transformation temperature [7], of RE-doped samples increased with increasing dopant content.…”

“…Thus, the Lu 3+ cation is smaller than that of Ca 2+ (1.00 Å) despite its larger atomic number. This suggests that small amount (~0.10 mol%) of Lu 3+ may be incorporated into the defect -alumina spinel lattice, as was the case in the Ca-doping system [7]. However, studies on the effect of dopants on the densification and microstructural evolution of RE-doped alumina nanopowders prepared from the sol−gel process have been lacking, although the role of RE-doped -aluminas have been extensively studied in relation to catalytic properties and thermal durability [16][17][18].…”

“…In addition, the exothermic DTA peak temperature (Pm), which deduces the -to- transformation temperature [7], of RE-doped samples increased with increasing dopant content. For example, the order of Pm for 0.30 mol% RE-doped samples without seeding was undoped (1151°C) < Lu-doped (1180°C) < Gd-doped (1198°C) < Nd-doped (1214°C).…”

“…We have shown that the use of M 2+ -doped -aluminas [3,7,8] synthesized through a polyhydroxoaluminum (PHA) sol-gel process [9][10][11] yields a fine grain size upon sintering due to the intimate mixing of dopants at an atomic level. Among the divalent cation dopants reported in our previous study, Ca 2+ is by far the best dopant for suppressing the grain growth of -alumina upon heating [7].…”