The invention relates to an alkaline-earth metal carbonate powder comprising a core consisting essentially of at least one alkaline-earth metal carbonate and a shell consisting essentially of at least one Group IV transition metal compound, to the method for manufacturing the same and to an improved method for preparing highly crystalline alkaline-earth metal containing mixed oxide powder. The highly crystalline mixed oxides obtained by means of the process according to the invention are used as starting material for high-performance dielectric, especially multi-layer capacitors, and for high performance dielectrics.