A structure and phase analysis investigation of the “1:1” ordered A2InNbO6 perovskites (A=Ca2+, Sr2+, Ba2+)

The structures of the Ba2InNbO6, Sr2InNbO6 and Ca2InNbO6 “1:1” complex perovskites have been refined from neutron powder diffraction data. Both the A=Ca and Sr compounds occur at room temperature in P121/n1 (a=ap+bp, b=–ap+bp, c=2cp) perovskite-related superstructures while the A=Ba compound occurs in the image, a=2ap, elpasolite structure type. In the case of the A=Ca compound, an extensive Ca2[(Ca2x/3In1−xNbx/3)Nb]O6 ‘solid solution’ field spanning compositions between Ca4Nb2O9 and Ca2InNbO6 in the CaO–InO3/2–NbO5/2 ternary phase diagram is shown to exist. Under the conditions of synthesis used, the ‘solid solution’ field stops just short of the ideal 1:1 Ca2InNbO6 composition.