Structure and properties of (Nd,Sr)(Al,Ta)O₃ (NSAT) substrate crystals

An emerging cubic substrate material (Nd,Sr)(Al,Ta)O₃ (NSAT) has been analysed using powder and single-crystal X-ray diffraction, transmission electron microscopy, infrared (IR) and ultraviolet-visible range ellipsometry as well as IR- and Raman spectroscopies. Based on this experimental characterization, the structure and vibrational properties are described with improved understanding. On a large length scale the NSAT substrate is found to have a basic simple cubic perovskite structure (a = 3.8427 Å) that, on a small length scale, is subdivided into superstructure ordered nanoscale domains with doubled lattice (unit-cell) parameter (a = 7.6855 Å). Ellipsometry and vibrational spectroscopy show absorption bands consistent with the expected structure type, however, the peak widths indicate significant local deviations from the perfectly ordered superstructure or ideal solid solution. Since the lattice parameter is unaffected, the observed inhomogeneity is not expected to affect the use of NSAT as a substrate for most applications.