Abstract: A process for producing a powder material for niobium-containing lead perovskite ceramics represented by the general formula:PbA.sub.x Nb.sub.1-x O.sub.3,wherein X=1/2 or 1/3, A represents at least one element selected from the group consisting of Fe, Co, Cr, Ni, Mn, Mg, Zn, Cd, Zr, In, Cu and Hf. A dried mixture of a sol or a suspension of a hydroxide a component A which has a lower activity than Pb and a niobic acid sol is first calcinated. A Pb compound is then added with the mixture and the resultant mixture is calcinated again.

Abstract: A process for producing a peroxoniobic acid sol which comprises: adding a strong acid, hydrogen peroxide and water to at least one niobium compound selected from the group consisting of niobium hydroxide, niobium oxide and niobium pentachloride to provide an aqueous solution of peroxoniobic acid; and then maintaining the aqueous solution at a temperature of 5.degree.-50.degree. C.

Abstract: A method of producing cobalt-modified magnetic particles is provided. The method comprises heating an aqueous suspension of ferric hydroxide at temperatures of 100.degree.-250.degree. C. at an alkaline pH in the presence of a water soluble organic or inorganic compound capable of forming complexes with iron as a growth regulating agent, and preferably also in the presence of .alpha.-ferric oxide seed crystals of minor axes not larger than 0.4 microns in average in amounts of 0.1-25 mole % in terms of the Fe content thereof in relation to the ferric hydroxide, converting the obtained .alpha.-ferric oxide into .gamma.-ferric oxide by reduction thereof followed by oxidation, maintaining an aqueous suspension of the .gamma.-ferric oxide at temperatures of 30.degree.-50.degree. C. at an alkaline pH in the presence of ferrous hydroxide and cobaltous hydroxide in amounts of 0.5-50 mole %, respectively, in relation to the Fe content of the .gamma.