Method of producing compound oxide by using partly citrating process

A method of producing a compound oxide of selected elements including:

• at least one element selected from the group consisting of thallium, bismuth, lead, antimony, yttrium, and other rare earth elements,
• at least one transition metal element;
• and
• at least one element selected from the group consisting of the alkali metal elements and the alkaline earth metal elements, said method comprising the following steps in the sequence set forth:
• reacting at least one starting compound with an amount of citric acid that is from 25 to 50% by weight of the weight equivalent amount required for forming a citrate derivative of said selected elements, thereby forming a partly citrated compound,
• said starting compound comprising a mixture of derivatives of each of said selected elements or a co-precipitate of derivatives of each of said selected elements,
• said derivative of each of said selected elements being selected from the group consisting of carbonate, basic carbonate, and hydroxide,
• and said co-precipitate of derivatives of each of said selected elements is selected from the group consisting of carbonate, basic carbonate and hydroxide,
• and calcining said partly citrated compound.