Experiments on the growth of (SrAl0.5Ta0.5O3)(1-x-y)(LaAlO3) (CaAl0.5Ta0.5O3)(y), perovskite crystals by the Czochralski and floating zone methods over a wide composition range are reported. The structure of these crystals was investigated using precise X-ray measurements at room temperature. The experiments allowed us to find regions on a SrAl0.5Ta0.5O3:LaAlO3:CaAl0.5Ta0.5O3 Composition triangle where solid solution exists and the type of lattice the crystals adopt. It was found that depending on the volume of the primitive perovskite unit cell, the crystals adopt cubic (Fm-3m+Pm-3m), tetragonal (P4/mbm) and orthorhombic (Pbnm) structures. We did not observe the expected temperature-induced second-order structural phase transitions occurring at the transition from the orthorhombic to tetragonal and from the tetragonal to cubic structures in the 20-600degreesC range. No tendency to form twins has been detected in the solid solution crystals with the cubic and tetragonal structures. The range of the lattice parameters' variation and the high melting point indicate that these crystals may be used as substrates for high temperature superconductors, manganites or GaN epitaxial layers because of their high thermal and chemical sability. (C) 2004 Elsevier B.V. All rights reserved.