Abstract: A beta and beta"-alumina precursor sol is prepared by controlled hydrolysis of chelated aluminum alkoxide in an alcohol solvent and, subsequently reacting it with a mixture of sodium, magnesium, and lithium alkoxides or acetates or a mixture thereof. The sol thus obtained can be converted into an amorphous transparent gel at low temperatures. This amorphous gel, crystallizes directly into crystalline beta-aluminas at about 1020.degree. C. On heating to about this temperature, crystalline beta and beta"-alumina are formed which are useful as solid electrolyte material in making a sodium-sulfur battery.