Oxide materials of general composition ABCO₄ (where A = Ca, Sr, Ba, B = La, Nd, Pr and C = Al, Ga) with the tetragonal perovskite–related K₂NiF₄ – type structure are considered as promising substrate materials for high temperature superconducting (HTSc) thin films, elements of thermal radiation receivers and other electronic devices due to their electrochemical and thermal properties and good lattice matching as well.

Crystals of high structural quality are required for such applications and characterisation of crystal lattice defects is of great importance. The growth of solid solution in the systems A_xA’_1-xBCO₄ or ABC_xC’_1-xO₄ gives the possibility of obtaining the proper lattice parameter by the selection of the A/A’ or C/C’ ratio [1]. The linearity of lattice parameters a and c for the whole concentration range x (0 ≤ x ≤ 1) in solid solutions of SrLaAlO₄–CaLaAlO₄, SrNdAlO₄–CaNdAlO₄, SrPrAlO₄–CaPrAlO₄, SrLaAlO₄–SrLaGaO₄ and SrLaAlO₄–SrLaFeO₄ was shown in [2].

In the present paper the Ca_0.5Sr_0.5NdAlO₄ single crystal grown by the Czochralski method in the [100] direction was investigated. The investigations were performed by conventional projection transmission x-ray topography and synchrotron radiation white beam topography in transmission and back reflection geometry.

The conventional projection x-ray topographs reveal growth striations with strong black or white diffraction contrasts distributed periodically in the form of concentric rings. The small spotty contrasts - probably associated with precipitates – can be recognised in the strips. Most of them are interconnected by linear contrasts, which could correspond to the dislocations.

In the white beam back reflection synchrotron radiation projection topographs the lines of stripes are well visible. Many spotty diffraction contrasts are seen. They probably correspond to the intersection of dislocations with the crystal surface or they are associated with the near surface precipitates.

Transmission synchrotron section topographs provided a good visibility of segregation fringes and other defects at the intersection of the sample by the incident beam. A characteristic observed effect was bending of the section image caused by strong lattice strains connected with segregations.

[1] A. Novoselov, G. Zimina, A. Filaretov, O. Shlyakhtin, L. Komissarova, A. Pajaczkowska, Mater. Res. Bull. 36 (2001) 1789.

[2] A. Novoselov, G. Zimina, L. Komissarova, A. Pajaczkowska, J. Crystal Growth 287 (2006) 305.

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