First Electrochemical Growth of δ-Al2O3 Single Crystal

Abstract

Single crystals of δ-Al2O3 were successfully grown for the first time by dc electrolysis of the Al3+ ion conducting Al2(MoO4)3 solid electrolyte at 11 V, 900 °C. δ-Alumina is the intermediate phase in the transformation from γ- to θ-alumina, and is stable only in the narrow calcination temperature range between 650 and 950 °C and has not been ever grown as a single-crystal form. Because it is necessary to heat the starting material above the melting point of alumina to grow a single crystal by the conventional methods via melt, single-crystal growth of the most stable α-Al2O3 has precedence over the intermediate phase such as δ-Al2O3. On the contrary, the presently developed electrochemical method can be simply applicable at moderate temperatures around 900 °C for the single-crystal growth, and, therefore, it becomes possible to grow artificially such an intermediate phase as δ-Al2O3 in a single-crystal form.