Abstract: The{hkl}_c X-ray diffraction peaks splitting due to the pseudocubic system in the LaAlO₃ single crystal wafer has been analyzed.It is found that the splitting for{hol}_c is simpler than that for other peaks.The splitting angle for {hol}_c is measured for a (ool)_c LaAlO₃ sample by the asymmetrical θ~2θ X-ray diffraction technology.The relation between the splitting angle and the rhombohedral lattice constant a in LaAlO₃ is established.The cubic degrees of an LaAlO₃substrate containing YBCO film is measured,with no destruction to the film and the substrate.The experimental technology here is very suitabler for researching the defect relation between the film and the substrate in the process of growing and annealing.

Key words: LaAlO₃ substrate, stauctural Parameter, asymmetrical X-ray diffraction