Fig. 1 X-ray diffraction patterns of initial mixtures corresponding stoichiometry of a NdSrAlO4 after sintering in air at 700, 900, 1050 °C for 5 h; b GdSrAlO4 after sintering in air at 1400 °C for 5 (1) and 15 (2) h

Fig. 2 SEM photographs of initial mixtures corresponding stoichiometry of GdSrAlO4 after sintering at 1400 °C a, a′; DySrAlO4 after sintering at 1400 °C b; 1500 °C c in air for 5 h

Fig. 3 X-ray diffraction patterns of initial mixtures corresponding stoichiometry of DySrAlO4 after sintering in air at 1300-1500 °C for 5 h as well as theoretical diffractogram

Fig. 4 Phase formation schemes, describing processes which are taken place under heat treatment of initial mixture of: a SrO:Gd2O3:Al2O3 = 1:0.5:0.5; b SrO:Dy2O3:Al2O3 = 1:0.5:0.5 at 1400 °C. Notes asterisks The compositions of determined phases are put according to data: opened diamond fixed by X-ray analysis; closed circle fixed by SEM/EDX method and reflected in Table 2; closed square the nominal composition of synthesis target product: a GdSrAlO4, b DySrAlO4

Fig. 5 Schematic illustration of the Gibbs energy of a equilibrium state of compound C in pseudo-binary system A-B; b metastable state of compound C in pseudo-binary system A-B in the case of stable compound D formation