Differences in the sintering mechanisms of $\alpha$- and $\gamma$-Al$_2$O$_3$ nanopowders after addition of Bi$_2$O$_3$

In this work, we experimentally studied the sintering of compacts of the composition $\alpha$-Al$_2$O$_3$ (96 mol.%)+Bi$_2$O$_3$ (4 mol.%) and $\gamma$-Al$_2$O$_3$ (96 mol.%)+Bi$_2$O$_3$ (4 mol.%) obtained by cold isostatic pressing at a pressure of 1 GPa. Depending on the type of Al$_2$O$_3$ crystal lattice, a significant difference was found in the nature of sintering and the final composition. A nonmonotonic nature of shrinkage during sintering of $\alpha$-Al$_2$O$_3$ with Bi$_2$O$_3$ around 1100$^\circ$C has been established.