Formation of continuous solid solutions with a tetragonal structure of K2NiF4-type was investigated by direct solid-state synthesis, carbonate precipitations, the freeze-drying method and the Czochralski crystal growth technique. In the systems of SrLaAlO4-CaLaAlO4, SrNdAlO4 CaNdlO(4), SrPrAIO(4)-CaPrAlO4, SrLaAlO4-SrLaGaO4 and SrLaAlO4-SrLaFeO4 solid solutions are formed in the whole concentration range (0.0 <= x <= 1.0) and in the systems of SrLaAIO(4)-SrLaMnO4 and SrLaAlO4-SrLaCrO4 in the limited compositional interval of (0.0 <= x <= 0.20) and (0.0 <= x <= 0.25), respectively, with composition dependency of lattice constants following Vegard's law. (c) 2005 Elsevier B.V. All rights reserved.